Understand the performance of valves: help you better choose valves

Why do we need to understand and consider the performance of the valve?

Valves have different requirements according to their types and uses, mainly including sealing, strength, regulation, circulation, opening and closing, etc. In the process of selecting the valve, in addition to the basic parameters and performance, the performance of the valve should also be considered. So what are the performance characteristics of different valves?

What are the types of valves?

First of all, let’s take a look at the valves, which are mainly divided into the following categories.
1. Cut-off valve category
Mainly used to cut off or connect the media flow. Including gate valves, globe valves, diaphragm valves, ball valves, plug valves, butterfly valves, plunger valves, instrument needle valves, etc.
2. Regulating valves
Mainly used to regulate the flow of media, pressure, etc.. Including regulating valves, throttle valves, pressure reducing valves, etc.
3. Check valve class
Used to stop the backflow of the medium. Including a variety of structure of the check valve.
4. Diverter valve class
Used to separate, distribute or mix media. Including a variety of structure of the distribution valve and trap.
5. Safety valves
Used for the safety protection of the medium when overpressure. Including various types of safety valves.

Gate valve

The valve opening is controlled by the up and down movement of the valve plate. The valve plate is like a gate. When the gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is, only rely on the medium pressure to press the sealing surface of the gate to the other side of the valve seat to ensure that the sealing surface is sealed, which is self-sealing. Most of the gate valves are forced to seal, i.e. when the valve is closed, it depends on external force to force the gate plate to the seat to ensure the sealing of the sealing surface.

Types of gate valves

According to the configuration of sealing surface can be divided into wedge gate type gate valve and parallel gate type gate valve. Wedge gate type gate valve can be further divided into: single gate type, double gate type and resilient gate type; parallel gate type gate valve can be divided into single gate type and double gate type. According to the thread position of the stem, it can be divided into two kinds of open stem gate valve and concealed stem gate valve. There are more domestic manufacturers of gate valves, and the connection size is mostly not uniform.
Performance characteristics
Advantages
1. Low flow resistance. The media channel inside the valve body is straight through, the media into a straight line flow, low resistance to flow.
2. Opening and closing with less effort. Is compared with the globe valve, because whether open or closed, the direction of movement of the gate is perpendicular to the direction of media flow.
3. The height is large, opening and closing time is long. The opening and closing stroke of the gate is larger, and the lowering is carried out by the screw.
4. Water hammer phenomenon is not easy to produce. The reason is that the closing time is long.
5. The medium can flow in any direction to both sides, easy to install. Both sides of the gate valve channel are symmetrical.
6. The length of the structure (the distance between the two connecting ends of the shell) is small.
7. Simple shape, short structure length, good manufacturing process, wide range of applications.
8. Compact structure, good rigidity of the valve, smooth passage, small flow resistance, stainless steel and hard alloy sealing surface, long service life, PTFE packing. Seal reliable. Operation is light and flexible.
Disadvantages
Easy to cause erosion and abrasion between the sealing surface, maintenance is more difficult. Larger dimension, need a certain space to open, long opening and closing time. The structure is more complicated.

Diaphragm valve

The structural form of diaphragm valve is very different from the general valve, is a new type of valve, is a special form of cut-off valve, its opening and closing member is a piece of diaphragm made of soft material, separating the valve body cavity from the valve cover cavity and driving parts, now widely used in various fields.

Commonly used diaphragm valve ➨ rubber-lined diaphragm valve, fluorine-lined diaphragm valve, unlined diaphragm valve, plastic diaphragm valve.
Diaphragm valves use corrosion-resistant lined valve body and corrosion-resistant diaphragm instead of spool assembly, using the movement of the diaphragm to play a regulatory role. Diaphragm valve body material using cast iron. Cast steel, or cast stainless steel, and lined with a variety of corrosion-resistant or wear-resistant materials. Diaphragm material rubber and polytetrafluoroethylene. Lined diaphragm corrosion resistance, suitable for strong acid. Strong alkali and other strong corrosive media regulation.
Performance characteristics
Advantages

• 1. Simple structure of diaphragm valve. Low fluid resistance. Flow capacity is larger than other types of valves of the same specification.
• 2. Suitable for corrosive. Viscous. Slurry media. 
• 3. The valve is easy to quickly disassemble and repair, replace the diaphragm can be completed in the field and in a short time.
• 4. Non-leakage, can be used for high viscosity and suspended particles in the regulation of media. The diaphragm isolates the media from the upper chamber of the valve stem, so there is no packing media will not leak.
• 5. Diaphragm valve flow characteristics close to the fast-opening characteristics, before 60% of the stroke is approximately linear, after 60% of the flow does not change significantly.
• 6. Pneumatic form of the diaphragm valve can also be equipped with feedback signals. Limiters and positioners and other devices to adapt to self-control. Program control or adjust the flow of the need.
• 7. Pneumatic diaphragm valve feedback signal using non-contact sensing technology. The product uses a film-type propulsion cylinder, instead of a piston cylinder, excluding the piston ring is easy to damage, causing leakage and can not push the valve open and close the drawbacks. When the air source failure, you can still operate the hand wheel to open and close the valve.

Disadvantages

• 1. Can not be used for high pressure occasions.
• 2. Due to the limitations of the diaphragm and lining materials, pressure resistance. Temperature resistance is poor, generally only applicable to 1.6MPa nominal pressure and 150 ℃ or less.

Ball Valves

Ball valve was introduced in the 1950s, with the rapid development of science and technology, production processes and product structure continue to improve, in a short period of 40 years, has rapidly developed into a major type of valve. In the western industrial countries, the use of ball valves is rising year by year. Ball valve in the pipeline is mainly used to do cut off. Distribution and change the flow direction of the medium, it only needs to use the operation of 90 degrees of rotation and a small torque to close tightly.

Performance characteristics
Advantages

• 1. small fluid resistance, full diameter ball valve basically no flow resistance.
• 2. Simple structure. Small volume. Light weight.
• 3. Tight and reliable. It has two sealing surfaces, and the sealing surface material of the ball valve is widely used various plastics, good sealing, can achieve complete sealing. It has been widely used in the vacuum system.
• 4. easy to operate, open and close quickly, from fully open to fully closed as long as the rotation of 90 °, easy to control from a distance.
• 5. easy to maintain, the ball valve structure is simple, the seal ring is generally movable, disassembly and replacement are relatively easy.
• 6. In fully open or fully closed, the ball and seat sealing surface and media isolation, the media through, will not cause erosion of the valve sealing surface.
• 7. Wide range of application, the passage diameter from small to a few millimeters, large to several meters, from high vacuum to high pressure can be applied.
• 8. Since the ball valve has wipability in the opening and closing process, it can be used in media with suspended solid particles.

Disadvantages
1. High processing accuracy and expensive cost
2. If there are impurities in the pipeline, it is easy to be blocked by impurities, resulting in the valve cannot be opened.
3. Because the main seat seal material of the ball valve is PTFE, it is inert to almost all chemical substances, and has a small coefficient of friction. Stable performance. Not easy to aging. Wide temperature range and excellent sealing performance of the comprehensive characteristics.
However, the physical properties of PTFE, including high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that the seat seal be designed around these properties. Therefore, when the seal material hardens, the reliability of the seal is compromised. Also, PTFE has a low temperature resistance rating and can only be used at less than 180°C. Above this temperature, the seal material will be damaged. Above this temperature, the sealing material will deteriorate. And considering the long-term use, it will generally only be not used at 120℃.
4. Its adjustment performance is poorer compared to globe valves, especially pneumatic valves (or electric valves).

Plug Valves

Plug valve is a fast opening and closing straight-through valve, because the movement between the rotary sealing surface with wiping effect, and in full opening can be completely prevented from contact with the flow of media, so it can usually also be used for media with suspended particles. Another important feature of the plug valve is that it is easy to adapt to multi-channel structure, so that a valve can get two. Three, or even four different flow channels. This simplifies the design of piping systems. This simplifies the design of piping systems and reduces the amount of valves and the number of connections needed in the equipment.

Performance features
Advantages

• 1. Plug valve for frequent operation, fast opening and closing. Light and convenient. 
• 2. Plug valves have low fluid resistance. 3.
• 3. Simple structure of the plug valve, relatively small size, light weight, easy to maintain.
• 4. Good sealing performance
• 5. Not restricted by the installation direction, the flow direction of the medium can be arbitrary.
• 6. No vibration, low noise.

Disadvantages
Ordinary plug valves rely on direct contact between the finely machined metal plug body and the valve body to seal, so the seal is poor, the opening and closing force is large, easy to wear, usually only for low pressure (not higher than 1 MPa) and small diameter (less than 100 mm) occasions.

Butterfly valve

Butterfly valve, also called flap valve, is a simple structure of the regulating valve, can be used for low-pressure pipeline media switch control of the butterfly valve refers to the closing member (valve flap or butterfly plate) for the disc, rotating around the valve shaft to achieve the opening and closing of a valve, the valve can be used to control air . Water. Steam. Various corrosive media. Mud. Oil. Liquid metal and radioactive media and other types of fluid flow. In the pipeline, it mainly plays the role of cutting off and throttling. Butterfly valve opening and closing member is a disc-shaped butterfly plate, in the valve body around its own axis rotation, so as to achieve the purpose of opening and closing or regulation. The butterfly plate is driven by the valve stem, and if it turns through 90°, it can complete opening and closing once. The flow of medium can be controlled by changing the deflection angle of the butterfly plate.

Performance characteristics
Advantages

• 1. Convenient and rapid opening and closing. Save effort. Small fluid resistance, can often operate. 2.
• 2. Simple structure, small size, short length, small volume, light weight, suitable for large diameter valves.
• 3. It can transport slurry and accumulate the least liquid at the mouth of the pipe.
• 4. Good sealing can be achieved under low pressure.
• 5. Good adjustment performance.
• 6. The effective flow area of the valve seat channel is larger when fully open, and the fluid resistance is smaller.
• 7. The opening and closing torque is small, because the butterfly plate on both sides of the rotating shaft is basically equal to the action of the medium, and the direction of torque generation is opposite, so it is less effort to open and close.
• 8. The material of sealing surface generally adopts rubber. Plastic. Therefore, the low pressure sealing performance is good. 9.
• 9. Easy to install.
• 10. Flexible and labor-saving operation, can choose manual. Electric. Pneumatic. Hydraulic method.

Disadvantages

• 1. Small operating pressure and temperature range.
• 2. Poor sealability.

Plunger valve

The plunger valve is composed of a valve body. Valve cap. Stem. Plunger. Orifice frame. Seal ring. Handwheel and other parts. When the handwheel rotates, the plunger is driven by the stem to move up and down in the middle of the hole frame to complete the opening and closing function of the valve. In the valve between the plunger and sealing ring using interference fit, through the adjustment of the flange bolts in the gland, so that the lateral force generated by the compression of the sealing ring and the valve body in the hole surface and the plunger outer circle seal, so as to ensure the sealing of the valve, eliminating internal and external leakage. At the same time, the valve opening torque is small, so that the valve can be opened and closed quickly.

Performance characteristics

• 1. The lift rod piston valve structure is simple and scientific. Safe and reliable, open and close especially easy and flexible, operate with less effort compared with the plunger valve opening and closing light. Fast and other advantages.
• 2. Unique sealing performance without leakage, the piston has a metal and non-metal multi-layer sealing structure composed of dual-effect function.
• 3. One-piece seat (cylinder sleeve) radial conical sealing surface, high height. Large contact area. Good performance.
• 4. Piston ring according to the different applicable media selection of materials can comprehensively improve its range of use, high temperature resistance. Wear-resistant. Corrosion resistance. Resilient performance, etc., by a long time use, piston ring such as wear and maintenance can be adjusted to increase the original state.
• 5. Maintenance replacement piston ring technology process is simple and convenient, the valve body does not need to be removed from the pipeline after the steam stop to remove the valve cover assembly can be replaced by a new piston ring repeatable use and other characteristics.

Check valve

Check valve is a valve that relies on the flow of the medium itself and automatically opens. Close the valve flap, used to prevent the backflow of the media valve, also known as check valve. One-way valve. Backflow valve. and back pressure valve. Check valve belongs to a kind of automatic valve, its main role is to prevent the backflow of media. Prevent the pump and drive motor reversal, as well as the release of the container media.

Check valve is used to prevent the backflow of the medium in the pipeline valve, it opens when the medium flowing downstream, and automatically closes when the medium flowing backwards. Generally used in the pipeline that does not allow the medium to flow in the opposite direction, to stop the backflow of the medium damage to equipment and machinery. When the pump stops running, it does not cause the rotary pump to reverse. In the pipeline, the check valve and the closed circuit valve are often used in series. This is due to the poor sealing of the check valve, when the media pressure is small, there will be a small part of the media leakage, the need for closed-circuit valve to ensure that the pipeline is closed. Bottom valve also in a kind of check valve, it must be submerged in water, specially installed in the pump can not self-priming or no vacuum pumping water in the front of the suction pipe.

Safety valve

Safety valve is a special valve in which the opening and closing parts are normally closed under the action of external force, and when the pressure of the medium in the equipment or pipeline rises above the specified value, it prevents the pressure of the medium in the pipeline or equipment from exceeding the specified value by discharging the medium outside the system. Safety valve belongs to the automatic valve category, mainly used in boilers. Pressure vessels and pipelines, control the pressure does not exceed the specified value, for personal safety and equipment operation plays an important role in the protection. Note that the safety valve must be pressure tested before use.

Performance characteristics
1. Heavy hammer lever type safety valve
Heavy hammer lever safety valve structure is simple, easy to adjust and more accurate, the added load will not be a large increase due to the rise of the valve flap, suitable for higher temperature occasions, the past is more common, especially in boilers and higher temperature pressure vessels. But the heavy hammer lever safety valve structure is relatively bulky, the loading mechanism is easy to vibration, and often produce leakage due to vibration; its return to the seat pressure is low, not easy to close and keep tight after opening.
2. Spring type safety valve
Spring-loaded safety valves are lightweight and compact, and have high sensitivity, and the installation location is not restricted, and because of the sensitivity to vibration is small, so it can be used for mobile pressure vessels. The disadvantage of this type of safety valve is that the added load will change as the valve opens, that is, as the valve flap rises, the compression of the spring increases, and the force acting on the valve flap increases. This is detrimental to the rapid opening of the safety valve. In addition, the spring on the valve will be affected by high temperature for a long time and the elasticity will be reduced. When used in high temperature vessels, often consider the spring insulation or heat dissipation, thus making the structure complex.
3. Pulse type safety valve
By the main valve and auxiliary valve, the auxiliary valve pulse action to drive the main valve action. Its structure is complex, usually only applicable to the safety discharge of a large number of boilers and pressure vessels.
The above three forms of safety valves, the more commonly used is the spring-type safety valve.

Directional valve (switching valve, diverter valve)

Directional valves are combined on the basis of several DC shut-off valve types and are used to change the flow direction of process media and to control the combined flow or diversion mode of multiplexed media. For example, the gear pump and polymer filter system fluid direction control and polymerization system in the process medium of multiple distribution, etc.. Directional valves are widely used in the chemical industry. Petroleum industry. Metallurgy. Power sector. Pharmaceutical industry. Beer. Foodstuffs. Dairy beverage. Cosmetics and all kinds of engineering supporting piping system.

Performance characteristics

• 1. Stainless steel material.
• 2. High polishing precision, can reach food grade. Drug grade requirements.
• 3. Can be configured according to the user’s actual control system to achieve fully automatic operation and improve work efficiency.
• 4. The shell and main parts are castings, strong structure, high strength and not easy to deformation, beautiful appearance.
• 5. Smooth and clean conveying channel, to ensure the smooth flow of materials, will not form a blockage.
• 6. In the occasion of pressure sealing requirements, special sealing structure can be configured to fully meet the requirements of use.

Instrumentation needle valve

Needle valve spool is a very sharp cone, like a needle into the valve seat, thus the name. Needle valve is an important part of the instrument measuring pipeline system, mainly globe valve and ball valve, its function is to open or cut off the pipeline pathway, is the power station. Oil refinery. Chemical devices and instrumentation measurement pipeline in an advanced connection of the valve.

Performance characteristics

• 1. Needle valve shape than other types of valves can withstand greater pressure, good sealing performance, so generally used for smaller flow, higher pressure gas or liquid media sealing.
• Needle valves are best used in conjunction with pressure gauges. The general needle valve shape are made into threaded connection.
• 2. Ferrule type instrument valve has easy installation and disassembly. Tight connection. Good for fire prevention. Explosion-proof and high pressure resistance. Good sealing performance and other advantages.
• 3. Needle shut-off valve has good sealing and long service life, even after the sealing surface is damaged, you only need to replace the wearing parts, you can continue to use.

Control valves

Control valves play a very important role in the automatic control of modern plants, whose production depends on the correct distribution and control of the flowing medium. These controls, whether it is the exchange of energy. The pressure reduction or the simple filling of a vessel requires some final control element to complete.
The first part is the sensitive element, which is usually a transmitter. It is a device that can be used to measure the process parameter being regulated, such as pressure. Liquid level or temperature. The output of the transmitter is sent to the regulating instrument, the regulator, which determines and measures the deviation between the given or desired value and the actual value of the process parameter, sending the correction signal one after another to the final control element, the regulating valve. The valve changes the flow of the fluid so that the desired value of the process parameters is reached.

Performance features
Simple flow path of the control valve. Low resistance, generally suitable for forward use (installation).
However, in high pressure drop occasions regulating valve reverse use to improve the unbalance force and reduce damage to the spool, but also to facilitate the flow of media. Avoid coking and clogging of the regulating valve.
In general, the regulating valve is not recommended for reverse use, only in high differential pressure. High viscosity. Easy to coking and suspended particles medium is recommended for reverse use. Reverse use, should be avoided for a long time under the small opening operation, especially in the commissioning should pay more attention.

Throttle valve

The shape and structure of the throttle valve (Choke valve) is no different from the globe valve, but the shape of their opening and closing parts are different. Most of the opening and closing parts of the throttle valve are conical and streamlined, through which the cross-sectional area of the channel is changed to regulate the flow and pressure. The throttle valve is used to reduce the pressure of the medium in case of great pressure drop.

Performance characteristics

• 1. the structure is simple, easy to manufacture and maintenance, low cost.
• 2. adjustment accuracy is not high, can not be used for regulation. 3.
• 3. the sealing surface is easy to erosion, can not be used to cut off the media.
• 4. Poor sealing performance.

Trap valve

The valve is temperature-sensitive according to the temperature change in the cavity, so that the bimetal will automatically deform when it encounters the corresponding temperature, driving the spool to do the reset movement to close the valve seat hole to close the removal of steam.
On the contrary, if there is condensation in the valve cavity, the temperature inside the cavity will not cause deformation of the bimetal, so that the valve spool and valve seat remain open, so the condensate will always be removed, and the temperature of the valve cavity will change immediately after the condensate is exhausted, and the deformation of the bimetal will immediately close the valve seat hole so that the repeated opening and closing to achieve the effect of drainage and gas blockage. It is suitable for any thermal steam pipeline with suspected condensate drainage and recovery.

Bimetal Steam Trap Operating Principle
Performance characteristics

• 1. Control fluid velocity of about 30m/S to prevent cavitation damage, fluid channel labyrinth type, constantly changing fluid direction; allow differential pressure of 25MPa.
• 2. The throttling surface is separated from the sealing surface, and different throttling elements are provided according to the flow rate of the evacuated water, and the surface hardening treatment of the inner components of the valve can reach HRC70, which enables tight closing and long life.
• 3. The valve body assembly adopts the structure of internal pressure sealing, the greater the pressure difference, the better the sealing.
• 4. The valve body assembly and the actuator adopt floating connection, which can eliminate the jamming phenomenon caused by the different centers of the spool and the push rod.

Pressure reducing valve

Pressure reducing valve has piston or diaphragm structure, the output pressure acts on the piston or diaphragm to overcome the adjustable spring force to make the balance. The secondary pressure is adjusted with the adjusting screw, and the set spring is loaded to open the main valve, allowing airflow from the initial pressure p1 input port to the output port of the secondary pressure p2. When the output port of the circuit connection reaches the set pressure, the air inside acts on the diaphragm and generates a lifting force relative to the spring force. If the flow rate decreases, p2 increases slightly, also increasing the force acting on the diaphragm relative to the spring force, and the diaphragm and valve are then lifted until they balance with the spring force again, and the air flow through the valve decreases until its consumption and output pressure remain in balance. If the flow rate increases, p2 decreases slightly, and this decrease causes the force acting on the diaphragm to decrease relative to the spring force, and the diaphragm and valve then drop until they are again in equilibrium with the spring force. This increased air flow passes through the valve until its consumption and output pressure are in balance. No air is consumed and the valve is closed.

Difference between pressure reducing valve and relief valve.

1. At standstill, the pressure reducing valve port is normally open, and the relief valve port is normally closed.
2. The pressure reducing valve controls the outlet pressure steadily, while the relief valve controls the inlet pressure steadily.
3. The pressure reducing valve port closes as the outlet pressure rises, and the relief valve port opens as the inlet pressure rises.
4. The inlet and outlet of the pressure reducing valve are pressure oil circuit, and the return oil through the pilot valve must be led back to the tank separately, while the relief valve flows back to the tank together with the outlet merge.

What are the connection methods of valves?

Nowadays, the application range of valves is getting wider and wider, and the corresponding valves should be used in different environments. And the whole valve in connection with the pipeline or equipment between different. Whether it is the installation or use and maintenance are required to pay attention to the valve connection is not appropriate, easy to happen valve run, bubble, drip, leakage and other phenomena. Therefore, valve users should be treated according to the specific situation.
There are many forms of valve connection, generally common valve connection methods are: flange connection, clamp connection, butt welding connection, threaded connection, ferrule connection, clamp connection, self-sealing connection and other forms of connection. This article will focus on the most common flange connection, butt-weld connection and threaded connection in the installation process is prone to problems, I hope it will help you.

Threaded Valves – Threaded connections

A simple connection method, often used for small valves. This connection is usually made by machining the inlet and outlet ends of the valve with tapered or straight pipe threads, which allows it to be connected to a tapered pipe threaded fitting or piping. Since this connection may have large leakage grooves, sealant, sealing tape or packing can be used to plug these grooves. If the material of the valve body is weldable, but the coefficient of expansion varies greatly, or the range of variation in operating temperature is large, the threaded connection must be honey sealed and welded. The threaded connection is mainly for valves with a nominal through diameter of 50 mm or less. If the through diameter is too large, it is very difficult to install and seal the connection. In order to facilitate the installation and removal of threaded valves, pipe fittings are available at the appropriate locations in the piping system. Valves with a nominal diameter of 50 mm or less can use pipe joints as pipe joints. The threads of the pipe joints connect the two parts of the connection together. 

Flange Valves – Flange Connection Method

Flange connection is the most used connection form in valves. It is easier to install and disassemble. However, it is heavier and more bulky than the threaded valves, and the price is higher accordingly. Therefore, it is suitable for pipeline connection of various diameters and pressures. However, when the temperature exceeds 350 degrees, the load on the bolts, gaskets and flanges is significantly reduced due to the slackening of the bolts, gaskets and flanges, and leakage may occur for flange connections that are subjected to large forces.

Welded Valves – Welded Connection

This type of connection is suitable for various pressures and temperatures, and is more reliable than flange connections when used under more stressful conditions. However, it is more difficult to disassemble and reinstall a welded connection, so its use is limited to applications where the valve can be operated reliably for long periods of time, or where the conditions of use are severe and the temperature is high. Such as thermal power stations, nuclear energy projects, ethylene projects on the pipeline. Welded valves with a nominal diameter of 50 mm or less usually have a welded socket to accept the load plane end of the pipe. As socket welding between the socket and the pipe to form a gap, so there is a possibility that the gap is subject to corrosion of certain media, while the vibration of the pipeline will make the connection part fatigue, so the use of socket welding is somewhat limited. In the nominal diameter is larger, the use of the conditions of loading, higher temperature occasions, the valve body is often used bevel to weld, at the same time, the welding seam has the original requirements, must be selected to complete the work of skilled welders.

How should the operation and maintenance of the valve in the process of operation?

The principles of maintenance during the operation of the valve are as follows.
① Keep the external and moving parts of the valve clean, and protect the integrity of the valve paint. The surface of the valve, stem and stem nut on the trapezoidal thread, stem nut and bracket sliding parts and gears, worm gear and other parts are prone to depositing a lot of dust, oil and media residues and other dirt, wear and corrosion of the valve. Therefore, the valve should always be kept clean. The general dust on the valve should be swept by brush and compressed air, and even brushed by copper wire until the processing surface and the matching surface show the metal luster and the paint surface shows the original color of paint. Steam trap should be in charge of a person, at least once a shift inspection; regularly open the flushing valve and steam trap bottom wire plug flushing, or regular disassembly down flushing, so as not to clog the valve with dirt.
② Keep the valve lubricated, valve trapezoidal threads, stem nut and bracket sliding parts, bearing bits, gears and worm wheel Langstroms meshing parts and other mating active parts need good lubrication conditions to reduce mutual friction and avoid mutual wear. For no oil cup or oil nozzle, easy to damage or lost in the operation of the parts, should be repaired with the lubrication system, to return to prove the unclogging of the oil circuit.
Lubrication parts should be regularly oiled according to the specific circumstances. Often open, high temperature valves suitable for a week to a month between refueling; not often open, not high temperature valve refueling cycle can be longer. Lubricants are oil, grease, molybdenum disulfide and graphite, etc.. Oil is not suitable for high-temperature valves; butter is also not very suitable, they will melt and lose due to high temperature. High temperature valves are suitable for adding molybdenum disulfide and wiping graphite powder. The exposed lubrication parts, such as trapezoidal threads, between the teeth and other parts if the use of butter and other grease, very easy to stain the dust, while the use of molybdenum disulfide and graphite powder lubrication is not easy to stain the dust and lubrication effect is better than butter, graphite powder is not easy to apply directly, available a little oil or water into a paste can be used.
Oil injection seal plug valve should be oiled according to the prescribed time, otherwise it is easy to wear and leakage.
③ Keep the two pieces complete and intact. The bolts of the flange and bracket should be complete and full buckle, and no loose phenomenon is allowed. The fastening nut on the handwheel should be tightened in time if it is loose, so as not to wear out the connection or lose the handwheel. After the handwheel is lost, it is not allowed to replace the handwheel with a live plate, and it should be matched in time. Packing differential pressure is not allowed to be skewed or no pre-tightening gap. Easily polluted by rain, snow, dust and other dirt environment, the valve stem should be installed to protect the cover. The scale on the valve should be kept intact and accurate. Valve seals, caps, pneumatic accessories, etc. should be complete and intact. Insulation jacket should be free of dents and cracks.
In addition, the valve does not allow knocking, supporting heavy objects or standing people, so as not to dirty the valve, damage the valve. In particular, non-metallic mesh doors and cast iron valves, it is more taboo.
Keep the routine maintenance of electric devices. Maintenance of electric devices, in general, not less than once a month. Maintenance content are: the appearance should be clean, no dust stained accumulation, the device is not stained by vapor, oil; sealing surface, point should be firm, tight. No leakage; lubrication parts should be greased as required, valve Xuan nut should be greased; electrical parts should be intact, no phase failure, automatic switch and thermal relay should not be off, the indicator light shows correct.

How to install the valve?

Valve installation directly affects the use of good or bad, because we must pay attention to the direction and location of the valve installation, installation and construction must pay attention not to touch the valve made of brittle materials, do a good job of all protective measures and a series of work. Below, we introduce the problems and details to pay attention to when installing the valve.
(1) Address and location
Many valves are directional, such as globe valves, butterfly valves, pressure reducing valves, check valves, etc.. If installed in reverse, it will affect the effectiveness and service life or not work at all, or even cause danger. Ordinary valves have directional markings on the valve body; otherwise, they should be correctly identified according to the working principle of the valve. The cavity of the stop valve is asymmetrical from left to right. The fluid should pass through the valve mouth from bottom to top, so that the fluid resistance is small, open with little effort, the medium does not press the packing after closing, easy to maintain. This is also the reason why the shut-off valve cannot be reversed. Other valves also have their own characteristics.
Valve installation position is easy to operate: even if the installation is temporarily difficult, the long-term work of the operator should be taken into account. The valve handwheel is flush with the hood to make the opening and closing of the valve easier. Ground valve handwheel should be upward, not tilted, so as not to operate inconveniently. Wall-mounted machine valves and equipment should also leave standing room for the operator. To avoid working in the air, especially acid and alkali, toxic media, etc., otherwise it is very unsafe. The gate should not be installed upside down, otherwise the medium will remain in the valve cover gap for a long time, easy to corrode the valve stem, there are certain process requirements are contraindicated. Also very inconvenient to replace the gasket. Exposed stem gate valve shall not be installed underground, otherwise the exposed stem will be corroded due to moisture. When installing lift check valves, ensure that the bonnet is vertical so that it can be lifted and lowered flexibly. For swing check valves, make sure the pin is in a horizontal position when installing so that it can swing flexibly. Pressure reducing valves should be installed vertically on horizontal pipes and should not be tilted in all directions.
(2) Construction work
Check the valve before installation, check the specifications and model, and make sure there is no damage, especially the valve stem. Rotate it several times to see if it is skewed, as the stem is more likely to twist during transportation. Also remove any dirt from the valve.
When lifting the valve, the rope should not be tied to the handwheel or stem to avoid damage to these parts, but to the flange.
The piping connected to the valve should be cleaned. Compressed air can be used to remove iron oxide chips, silt, weld slag and other debris. This debris not only tends to scratch the sealing surface of the valve, but large debris particles can also block small valves and make them ineffective. When installing the spiral valve, the gasket should be wrapped around the pipe threads, do not enter the valve, so that the valve does not accumulate scale to affect the flow of media.
When installing the flange valve, pay attention to symmetry and tighten the bolts evenly. Valve flange and pipe flange should be parallel and have reasonable clearance to avoid excessive pressure or even valve cracking. Special attention should be paid to valves of brittle and low strength materials. Valves that need to be welded to the pipeline need to be spot welded first, and then the closing part needs to be fully open and then welded.
(3) Protective measures
Some valves also require external protection, namely insulation and cold retention. Sometimes hot steam pipes are added to the insulation. The type of valve that needs to be kept hot or cold depends on the production requirements.
In principle, if the medium temperature inside the valve decreases too much, it will affect production efficiency or freeze the valve, should be insulated or even mixed heat; the valve is exposed, which is not conducive to production. Or cause frost and other undesirable phenomena, need to be refrigerated. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; refrigeration materials include cork, perlite, foam, plastic, etc.
(4) Bypass and instrumentation
In addition to the necessary protection facilities, some valves are equipped with bypass and pressure gauges. Bypasses are installed. Facilitate the maintenance of traps. For other valves, bypasses are also installed. The bypass installation depends on the valve condition. Importance and production requirements.
(5) Replacement of packing
Stock for the valve, some packing is not good enough, some do not match with the media used and need to replace the gasket.
Valve manufacturers can not consider the use of several different types of media, stuffing box is always filled with ordinary packing, but the use of the packing to be compatible with the media.
When replacing the gasket, press a circle. The seam of each circle should be 45 degrees, and the circle and the circle should be opened 180 degrees. The height of the packing should take into account the space for the gland to continue compaction. Currently, the packing chamber at the bottom of the stuffing box should have sufficient depth. This depth can usually be 10-20% of the total depth. Packing chamber depth. For demanding valves, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees. In addition to the above packing, three rubber O-rings can be installed. Use ground packing such as laminated PTFE ring and bowl-shaped nylon ring according to specific conditions. Outside the ordinary asbestos packing, adding a layer of PTFE raw material tape can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.
The above introduces the problems and details to be noted when installing the valve. In the pressure of seasoning, while turning the valve stem, keep around evenly, prevent too dead force evenly tighten the cap, do not tilt.

Installation requirements of the valve

The installation of the valve should be carried out in accordance with the valve instruction manual and relevant regulations. The construction process should be carefully checked and carefully constructed. Before the installation of the valve, the test pressure should be qualified before installation, carefully check the specifications of the valve. Model is consistent with the drawings, check whether the valve parts are intact, open and close the valve whether the rotation is flexible and free, sealing surface damage, etc., to confirm that there is no error, you can proceed with the installation.
When the valve is installed, the valve operating mechanism from the operating floor is best in about 1.2m, will be flush with the chest. When the center of the valve and the handwheel from the operating ground more than 1.8m, should operate more valves and safety valves set up operating platform. The pipeline with more valves, the valve is concentrated on the platform as much as possible for operation.
For more than 1.8m and infrequent operation of a single valve, a sprocket can be used. Extension rod. Activity platform and activity ladder and other equipment. When the valve is installed below the operating surface, should be set to extend the rod, ground valve should be set to the ground well, for safety reasons, the ground well should be covered.
The stem of the valve on the horizontal pipeline, it is best to vertical up, should not be installed down the stem. Stem downward installation, inconvenient operation, inconvenient maintenance, but also easy to corrode the valve out of the accident. Floor valves should not be installed skewed to avoid inconvenient operation.
Side by side on the line of the valve, there should be operation. Maintenance. Disassembly of the empty space, the net distance between the handwheel is not less than 100mm, such as narrow pipe distance, the valve should be staggered arrangement.
The opening force is large, the strength is low. Brittle and weight of the valve, the valve should be set up to support the valve frame before installation, to reduce the start-up stress.
When installing the valve, use pipe wrenches for pipes close to the valve, while the valve itself should use ordinary wrenches. At the same time, when installing, make the valve in a semi-closed state to prevent the valve from rotation and deformation.
The valve should be correctly installed so that the internal structure form in line with the flow of the medium, the installation form in line with the special requirements of the valve structure and operational requirements. Special attention should be paid to the valve with media flow requirements should be installed in accordance with the requirements of the process pipeline. The arrangement of the valve should be convenient and reasonable, the operator is easy to access the valve, for lifting stem type valves, to leave room for operation all the valve stem should be installed as far up and perpendicular to the pipeline.

Installation of the valve connection surface

The installation end of the valve using threaded connection, should make the thread screwed into the valve the appropriate depth, the thread screwed into too deep pressure seat, will affect the seat and gate with a good fit, screwed into too shallow, will affect the sealing reliability of the joint, easy to introduce leakage. At the same time the thread sealing material should be used to be teflon raw tape goods sealant, pay attention not to give the sealing material to the valve cavity.
For the flange end connection of the valve, the first thing to find the flange connection surface, the cover is perpendicular to the pipeline, and the bolt hole should be right. The valve flange should be parallel to the pipe flange, the flange gap is moderate, there should be no mismatch, tilt and other phenomena, the flange between the heart gasket should be placed in the center, not skewed, and the bolts should be tightened symmetrically and evenly. Prevent the forced connection tightening during the valve installation, producing an additional residual force.
Thoroughly remove dirt from the inner wall and external threads of the pipe before installation; remove burrs, foreign objects, etc. that hinder the flow of media and may affect the operation of the equipment, and blow clean the dirt, slag and other debris in the pipeline before the pipe is connected. Prevent damage to the sealing surface of the valve or block the valve.
Installation of welded end connection valves, should be grouped first after spot welding both ends of the valve weld, open the valve, and then weld the weld according to the welding process card, after welding the appearance of the weld and the intrinsic weld quality inspection to ensure that no porosity, slag, cracks, etc., when needed, the weld should be ray or super control inspection

Installation of heavier valves

Installation of heavier valves (DN > 100), the application of lifting tools or equipment, lifting ropes should be tied to the valve flange or bracket, should not be tied to the valve handle stem to avoid damage to the valve.

What are the general requirements for the installation of valves?

The general requirements of valve installation. The most suitable installation height. Horizontal pipeline on the valve. Stem direction as follows.

• (1) The valve should be located in easy access. Easy to operate. Maintenance of the place. Rows of pipelines (such as the pipeline in and out of the device) on the valve should be arranged centrally, and consider setting up operating platforms and ladders. Parallel arrangement of the valve on the pipeline, the centerline should be taken as far as possible. The net distance between the handwheels should not be less than 10Qmm, in order to reduce the pipeline spacing, the valves can be staggered arrangement.
• (2) The installation position of the frequently operated valves should be easy to operate, the most suitable installation height is 1.2m up and down from the operating surface. When the height of the center of the valve handwheel exceeds 2m from the operating surface, a platform should be set up for centrally arranged valve groups or frequently operated individual valves and safety valves, and appropriate measures (such as sprockets, extension bars, movable platforms and movable ladders, etc.) should be taken for individual valves that are not frequently operated. The chain of the sprocket should not impede passage. Valves on pipelines and equipment for hazardous media shall not be installed within the height of the human head to avoid bruising the head or directly injuring the human face due to valve leakage.
• (3) Valves for isolation equipment should be directly connected to the equipment orifice or close to the equipment. With extremely hazardous . Highly hazardous toxic media equipment connected to the valve on the pipeline, should be directly connected to the equipment valley mouth, the valve shall not use the sprocket manipulation.
• (4) Accident handling valves such as fire water with valves . Fire steam two valves, etc. should be decentralized, and to take into account the safe operation of the accident. This type of valve should be arranged behind the control room. After the safety wall, outside the door of the plant, or a certain safety distance from the accident; so that when a fire accident occurs, the operator can safely operate.
• (5) In addition to the process has special requirements, the tower . Reactor. Vertical vessels and other equipment on the bottom of the pipeline valve, shall not be arranged in the skirt seat; (6) from the dry pipe on the lead-in, or a certain safety distance from the accident; so that the operator can safely operate in the event of a fire accident; (5) except for special requirements, the tower.
• (6) From the dry pipe on the horizontal branch of the shut-off valve, should be located near the root of the horizontal pipe section;.
• (7) Lift check valve should be installed in the horizontal pipeline, vertical lift check valve should be installed in the pipe media flowing from the bottom up on the vertical pipeline. Swing check valve should be installed in the horizontal pipeline as a priority, can also be installed in the pipe medium bottom-up flow of the vertical pipeline; bottom valve should be installed in the installation height of the centrifugal pump suction, can choose butterfly check valve; pump outlet and the diameter of the connected pipeline is not the same, can choose reducer check valve.
• (8) Arranged around the operating platform of the valve handwheel center from the edge of the operating platform should not be greater than 450mm, when the valve stem and handwheel into the platform above and the height of less than 2m, should make it does not affect the operation and passage of the operator.
• (9) The valve of the underground pipeline should be located in the pipe trench or valve well, if necessary, should have a valve extension pole. Firewater valve wells should be clearly marked.
• (10) The valve on the horizontal pipeline, the valve stem direction can be determined in the following order: vertical up; horizontal; upward tilt 45 °; downward tilt 45 °; shall not be vertical down.
• (11) The stem is installed horizontally open stem type valve, when the valve is opened, the stem shall not affect the passage.

Check valve installation needs to pay attention to the place

• (1) Installation position. Height. Inlet and outlet direction must meet the design requirements, pay attention to the direction of media flow should be consistent with the direction of the arrow marked on the valve body, the connection should be solid and tight.
• (2) The appearance of the valve must be checked before installation, the valve nameplate should comply with the current national standard “General Valve Marking” GB 12220. For working pressure greater than 1.0MPa and in the main pipe to play a cutting role in the valve, the strength and tightness test should be conducted before installation, qualified before use. Strength test, the test pressure of 1.5 times the nominal pressure, the duration of not less than 5min, the valve shell. Packing should be no leakage for qualified. Tightness test, the test pressure of 1.1 times the nominal pressure; test duration in accordance with the requirements of GB 50243.
• (3) In the pipeline do not make the check valve to bear the weight, large check valve: should be independently supported, so that it is not affected by the pressure generated by the pipe system.

Technical requirements for valve installation

• 1. Directionality. General valve body has a sign on the valve body, the arrow points to the direction of forward flow of gas. Special care must be taken not to install the reverse. Because there are a variety of valves require one-way flow of gas, such as safety valves. Pressure reducing valve. Check valve. Throttle valve, etc., for the shut-off valve in order to facilitate the opening and maintenance, but also require gas from the bottom up through the valve seat, but the gate valve. Plug installation, not restricted by the direction of flow.
• 2. Installation location. To valve long-term operation and maintenance considerations, as far as possible to facilitate the operation and maintenance, but also pay attention to the assembly of the appearance of the beauty. Valve handle direction can be vertical up, can also be tilted to a certain angle or placed horizontally, but the handwheel must not be down to avoid face-up operation; floor valve handwheel is best flush chest high, easy to open and close; open stem gate valve can not be used underground to prevent the stem from corrosion. Some valves have special requirements for installation location, such as pressure reducing valves require upright installation on the horizontal pipeline, shall not be tilted, lift check valve requires vertical valve flap; swing check valve requires the pin level. In short, according to the principle of the valve to determine its installation position, otherwise the valve will not work effectively, or even not work.
• 3. Installation of the plug. Verify the specifications, identify any damage, remove the threaded capping and excessive grease and debris in the threads, and test the sealing performance of the plug. The gas plug in the installation must pay attention to the appropriate force, according to the size of the plug specifications to choose different specifications of pipe pliers or wrenches for installation.
• 4. When the installation of silk buckle valve, the valve company should ensure that the thread is intact; wrench can be used when possible, do not use pipe wrench to avoid damage to the appearance of the valve body.
• 5. Flange type valve installation, must ensure that the two flange sections are parallel to each other and in the same axis, tighten the bolts should be crossed, so that the valve end face is evenly stressed.
• 6. Flange and threaded connection of the valve should be installed in the closed state. Butt-welded valves connected to the pipeline, the bottom of the weld should be used argon welding welding to ensure internal cleanliness, welding, the valve should not be closed to prevent heat deformation.
• 7. In general, the valve is directly connected to the corrugated expansion joint, so the pipe on both sides should be cut off according to the size of the valve and the corrugated expansion joint and the flange and gasket, leaving the installation position.
• 8. When lifting the valve, the rope should not be tied to the first wheel or stem to prevent damage, should be lightly lifted, lightly placed, not collision. When placed on the piers, according to the required elevation pad stable, pad flat. Under the valve must have a solid pier or bracket to hold the valve, do not allow the valve overhang to produce stress.

How to accurately identify the valve?

Marking and identification of valves

Usually according to the signs and signs on the valve and the valve paint, you can directly identify the valve type, structural form, material, nominal diameter, nominal pressure (or working pressure), applicable medium, temperature and closing direction.

I. The understanding of signs

The label is fixed on the valve body or handwheel. The data of the label is relatively complete, reflecting the basic characteristics of the valve. The manufacturers on the label can provide the wearing parts, drawings and information of the valve. The type of gasket, filler and material to be replaced, as well as the material of other parts to be replaced, can be determined according to the conditions of use provided on the label.

II. The valve logo

1. Symbols for general valves Table 1-26 lists the symbols that must be used for general valves and that can be used optionally. The specific marks of general valves are as follows: (1) Items 1 to 4 in Table 1-27 must be used as signs, for the DN≥50mm valve, should be marked on the valve body; For valves DN < 50mm, whether to mark them on the body or on the label shall be specified by the product designer. (2) Items 5 and 6 of Table 1-27 must be used only when specified in a class of valve standards and shall be marked on the body and flange respectively. (3) If there are no special provisions in various valve standards. Items 7 to 19 in Table 1-27 indicate the flags to be used as required. Mark on body or plate when required. Table 1-26 General valve logo items (GB12220-89)

project	mark	project	mark	project	mark
1	Nominal diameter (DN)	8	Thread code	15	Code for lining material
2	Nominal pressure (PN)	9	Extreme pressure	16	Quality and test marking
3	Material code for pressurized parts	10	Factory No.	17	Inspector’s mark
4	Name or trademark of manufacturer	11	Standard no.	18	Manufacturing year, month
5	Arrow of medium flow direction	12	The smelting furnace	19	Flow characteristics
6	Seal ring (gasket) code	13	Internal material code
7	Limit temperature (℃)	14	Location,

Note: Nominal pressure casting mark value on valve body equal to 10 MPa number shall not be preceded by code “PN” when set below nominal size number. ① In different positions, you can attach any sign in the table. For example, any sign placed on the valve body may also be repeated on the label. ② As long as the attached symbol is not confused with the symbol in the table, you can attach any other symbol. For example, product model. For pressure reducing valves, the mark on the valve body shall, in addition to the provisions of Table 1-27, also be: A. Date of delivery; B. Applicable medium; C. Outlet pressure. Steam trap logo The logo may be placed on the valve body or on the label as specified in Table 1-27. The safety valve shall be marked in accordance with Table 1-28.

Table 1-27 Signs of steam trap (GB12249-89)

project	Must be used logo	project	Must be used logo
1	Product model	1	The valve body material
2	Nominal diameter	2	Maximum permissible pressure
3	Nominal pressure	3	Maximum permissible temperature
4	Name and trade mark of manufacturer	4	Maximum drainage temperature
5	Arrow indicating direction of medium flow	5	Factory number and date
6	Maximum working pressure	–
7	Maximum operating temperature	–

Table 1-28 Signs of safety valves (GB12241-89)

project	Logo on valve body	project	Logo on valve body
1	Nominal diameter DN	1	The valve maximum allowable operating temperature (℃)
2	The valve body material	2	Setting pressure (MPa)
3	Name and trade mark of manufacturer	3	Reference standard number
4	When the inlet and outlet connecting parts of the same size or pressure level, there should be an arrow indicating the direction of medium flow	4	Manufacturer’s reference model
–	–	5	Rated displacement coefficient or rated displacement for reference media
–	–	6	Flow channel area (mm2)
–	–	7	Opening height (mm)
–	–	8	Over a percentage of pressure

2. Signs of power station valves General signs of power station valves can refer to the provisions of GB12220-89. Qualified products of power station valves should be affixed with metal labels, as shown in Table 1-29.

Table 1-29 Signs on the power station valve label (JB/T3595-93)

project	mark	project	mark	project	mark
1	The product name	4	Nominal diameter	7	The valve body material
2	Product model or drawing number	5	Nominal stress or job stress	8	The manufacturing date
3	Product number	6	Maximum operating temperature	9	Factory name

For the regulating valve, in addition to the provisions of Table 1-29 signs on the sign, should also be: (1) the maximum allowable pressure difference; ② Product rated flow coefficient. The signs on the safety valve label are listed in Table 1-30.

Table 1-30 Signs on safety valve labels (ZBJ98013-89)

project	mark	project	mark	project	mark
1	Name and model of safety valve	4	Nominal pressure	7	Discharge coefficient
2	Factory number	5	Throat diameter of seat	8	Manufacturer’s name or logo (registered trademark)
3	The factory monthly	6	Members of the highly	9	Suitable temperature

3. The sign of the opening and closing direction of the handwheel hand wheel has an arrow indicating the direction of the valve closing and additional “close” word, the arrow indicates the direction of the handwheel rotating closing valve; Otherwise, the direction of valve opening. 4. The valve opening and closing groove mark ball valve, butterfly valve stem and plug valve plug cone square end face carved with a groove, the groove direction and the direction of the valve inlet and outlet consistent, indicating that the valve is open; If the direction of the groove is perpendicular to the direction of the inlet and outlet of the valve, the valve is closed. The opening and closing parts of the three-way valve are L and T, and the L or T groove marks are carved in the same direction as the opening and closing parts. The valve switching and switching can be judged by the direction of the groove. 5. Throttle valve, dark rod gate valve, regulating valve, butterfly valve and other valves are equipped with an opening indicator reflecting the degree of valve opening and closing. The opening indicator has the disc type, and the ruler type and other forms, assembled on the handwheel, valve stem, bracket. When the opening indicator is zero, the valve is closed. 6. Mark of material code of pressurized parts Material code of pressurized parts is marked on the valve body, and the meaning of material code of valve body is shown in Table 1-12.

III. Valve paint identification

Before leaving the factory, different parts of the valve should be painted with different colors according to the valve body material, sealing surface material and transmission mechanism, so as to facilitate identification. To identify the valve body materials, paint the unprocessed surface of the valve body and bonnet according to the colors specified in Table 1-31. Sealing surface identification Paint Applies to the handwheel, handle, or wrench according to Table 1-32. The paint color of the transmission mechanism is stipulated as follows: electric device, ordinary type painted medium gray; Three in one (outdoor, explosion-proof, anti-corrosion) painted sky blue; Pneumatic, hydraulic, gear drive and other transmission mechanism with the valve product coloring.

Table 1-31 Body material identification

The valve body material	Identify paint color	The valve body material	Identify paint color	The valve body material	Identify paint color
Gray cast iron, malleable cast iron Nodular cast iron	black silver	Carbon steel Acid resistant steel, stainless steel	In the gray Sky blue	Alloy steel	In the blue

Table 1-32 Identification of sealing surface materials

Sealing material	Identify paint color	Sealing material	Identify paint color
Copper alloy Tin-based bearing alloy (Babbitt) Acid resistant steel, stainless steel Nitriding steel, boronizing steel carbide	The big red Pale yellow Sky blue Sky blue Sky blue	Monel alloy plastic rubber Cast iron	Dark yellow purple Medium green, black

Note: 1. If the sealing surface material of the auxiliary and the opening and closing parts is different, please paint the color according to the low hardness material. 2. Check valve, coated on the top of the valve cover; The relief valve, pressure relief valve, trap is coated on the bonnet or bonnet.

IV. The identification of materials

Material identification of valve parts is an important project in valve repair, such as sealing surface surfacing, valve body repair welding, etc., need to first understand the material of the mother, in order to choose electrode. Here introduces several material identification methods: 1. Chemical analysis with chemical analysis method to analyze the content of various elements in the material, according to the material standard, check the table to determine the material brand. 2. Spectral identification of the emission spectrum characteristics of materials under high temperature and high energy excitation. The alloying elements can be qualitatively and semi-quantitatively analyzed by spectral identification. The carbon content in steel cannot be measured. 3. Spark identification The use of steel in grinding wheel flying out of the fine powder, rapid oxidation in the air and burst spark characteristics to identify materials. The shape and color of the sparks vary from steel to steel. Carbon in steel is the main element causing spark burst. In carbon steel with carbon content below 0.6%, the number of spark streamlines and pollen increases gradually, and the brightness increases with the increase of carbon content. For experienced workers, the identification accuracy of carbon content can reach 0.05%; But the ability to distinguish alloying elements is poor. Therefore, spark identification and spectral identification are usually combined to identify steel numbers. Soak the material in solvent and corrosive liquid, according to the deformation and corrosion degree of the material to identify the material, according to the corrosion resistance of different materials in the manual to be distinguished, 5. Combustion identification using the combustion properties of materials to identify materials, commonly used metal materials are not combustible. Rubber and plastics burn easily and are used as linings, seals, gaskets, fillers, etc. in valves, as shown in Table 1-33. In the premise of not damaging the valve and material, the use of various characteristics of material performance to identify, as shown in Table 1-34. 7. Section identification from the sample section color, grain thickness, edges and corners and other characteristics to see the table material. The steel with low carbon content has fine grain and gray color. High carbon content of steel, section grain slightly coarse, slightly white color. Alloy steel section, generally fine grain; High – speed steel has finer grains.

Table 1-33 Identification method of rubber and plastic combustion

varieties	Burn easily	Fireworks color	From out the ability	Post-combustion shape	Odor characteristics
Natural rubber	easy	Black smoke, dark brown flame	There is no	softening	The characteristic stench of natural rubber
Styrene butadiene rubber	easy	Black smoke	There is no	softening	Similar to natural rubber odor, with the smell of styrene
Nitrile rubber	easy	Black smoke	There is no	softening	There is a stench of nitride
neoprene	More difficult to	Black smoke, orange flames	There are	softening	A pungent stench of fluorine
Butyl rubber	easy	Smoke-free. Rose flame	There is no	The molten	Not a strong odor
thiokol	easy	Smokeless, brimstone purple flame	There is no	–	There is a strong irritating odor of sulfur dioxide
Silicone rubber	easy	white	There is no	Softened and grayish	It smells really bad
Fluorine rubber	difficult	–	There are	–	–
Nylon (polyamide)	More difficult to	Black smoke, blue flame tip yellow	There are	softening	There is a smell of burning wool

Note: PTFE does not burn

Table 1-34 Nondestructive identification

Material performance characteristics	Methods of identifying materials
Material oxidation rust	Carbon steel rusts more easily than cast iron and alloy structural steel Alloy structural steel is inferior to stainless acid – resistant steel Tonghe copper alloy is not easy to rust in the air, and it is easy to grow a layer of green moss over a long time
Material surface characteristics	The casting is rougher than the forgings, and there are traces of casting mouth, riser and sand on the surface of the casting Cast steel is brighter and finer than cast iron. Cast iron is dull and loose in texture Aluminum has a white and light surface The surface of purple steel is purplish brown Brass has a yellow surface White copper is almost white with a yellowish tinge
Material percussion sound	Usually with the increase of carbon content, the sound of the material gradually becomes loud, low carbon steel sound low, high carbon steel sound sharp
Magnetic properties of materials	Carbon steel can be attracted by a magnet Alloy stainless steel, ferritic shape and Martensite stainless steel, such as Cr17Ni2, 1Cr13, 2Cr13 and other steel can be attracted by magnets; And austenitic stainless steel is not magnetized, such as 1Cr18Ni9, 1Cr18Ni8Ti steel
The density of material	According to the formula “mass = density × volume”, the material can be identified by the method of calculating density by weighing. The density of the material can be found out from the relevant data The use of different materials density, the solid in liquid sink and float method can also identify materials, such as mercury density is 13.6g/cm2 tungsten-cobalt alloy density is greater than this value. Stellite is less dense than that, sinking into the mercury and floating on it

The section grain of steel casting is fine, the color is silver gray, sharp edges and corners, and the powder grains filed by the file become edges and corners. The section grain of gray cast iron is very fine, the color is gray black, there are silver small flash points, and the iron filings filed by the file become powder particles. Malleable cast iron is white cast iron after malleable annealing, so that the graphite in the cast iron exists as flocky, with high strength and certain plasticity and toughness. Nodular cast iron is added in molten iron spheroidizing agent, so that the graphite in cast iron is spherical distribution between the matrix and its performance is better than malleable cast iron. Carburizing layer, nitriding layer thickness can also be identified by section, carburizing surface layer organization fracture is brittle fracture, bright color, flat surface. The fracture of nitriding layer is plastic fracture with no bright color and rough surface. 8. Hardness identification with instruments or experience to determine the hardness of materials, to achieve the purpose of distinguishing grades. The hardness of steel reflects the carbon content to a certain extent. High carbon content leads to high hardness. The fitter files the steel and can judge the hardness of ordinary steel roughly by experience. 9. Steel paint mark On the surface of steel coated with various colors of paint, is a mark to distinguish the steel brand. This method is widely used in pipes and profiles, as shown in Table 1-35. 10. The material selection of the main parts of the valve is an important link in the design of the valve, but also the basis of valve repair, the data of the valve design to identify the valve provides an important reference value.

Table 1-35 Common metal material paint marks

Material mark	Color tag	Material mark	Color tag
High quality carbon structural steel 5 ~ 15 20 ~ 25 30 ~ 40 45 ~ 85 15 mn ~ 40 mn Alloyed structural steel Chrome steel Chrome vanadium steel Molybdenum steel Chrome molybdenum steel Molybdenum chrome vanadium steel Chrome molybdenum steel Chromium molybdenum aluminum steel	white Brown + green White + Blue White + brown Article 2 the white Green + yellow Green + Black purple Green + purple Purple + brown Yellow + purple	Alloyed structural steel Chromium molybdenum tungsten vanadium steel Manganese steel Stainless acid resistant steel Chrome steel Chrome molybdenum steel Cadmium nickel steel Cadmium nickel titanium steel Molybdenum chrome vanadium steel Cadmium nickel molybdenum titanium steel Heat resistant leather steel Chrome molybdenum steel Molybdenum chrome vanadium steel	Purple + Black Yellow + blue Aluminum wide strip + black narrow strip Aluminum wide strip + white narrow strip Aluminum wide strip + red narrow strip Aluminum wide strip + blue narrow strip Aluminum wide + red narrow + yellow narrow Aluminum wide strip + purple narrow strip Red wide bar + green narrow bar Aluminum wide strip + purple narrow strip

VI. The identification of valve class

To correctly identify valves, it is necessary to have certain practical experience and basic knowledge, which can be identified with the help of drawings and samples of valves. The valve sample provides the valve construction diagram, installation size, type, model, nominal pressure, nominal size, the name and material of the main parts and the scope of use, etc. For repairers with certain experience, they can also identify the type and model of the valve by using its appearance without disassembling the valve, as well as the general scope of application. Usually, partial herringbone valve body globe valve, throttle valve and lifting check valve, which is lifting check valve stem; The valve disc is conical, there is an opening indicator for the throttle valve; Disc without conical (except needle valve), no valve opening indicator for globe valve. The valve shape is positive herringbone, the lining of the channel is diaphragm valve (roof type); The center of the valve body is cylindrical, the channel is straight-through, the opening and closing parts are plate shaped, the valve body is higher for the gate valve; The valve body is conical, the stem is short, the opening and closing parts are conical for the plug valve; The valve body is generally composed of two halves, the valve stem is short, the opening and closing parts are spherical for ball valve; The valve body is composed of two halves, no stem, large diameter, there are more than two valves in the valve body, this is the swing multi-valve check valve; The bottom of the valve is generally spherical funnel shape, the upper part of the opening is the bottom valve (a check valve); The valve body is drum shape and no stem, the body of the valve disc rotation around the fixed axis for the swing check valve, the valve body is short tubular, stem, closing parts for butterfly and rotation around the fixed axis for the bottom valve. Usually, the valve body channel is a right Angle, the stem has a spring, and a seal is a spring safety valve; The lever type safety valve with lever and hammer; The valve body shape is different, no stem, the valve structure is special trap. Small diameter forged valve, the valve body shape difference is not big, can have stem and from the channel observation opening and closing parts to be identified. Three – way or four – way valves, generally ball valves and plug valves. Depending on its opening and closing parts are spherical or conical to distinguish. According to the shape and channel of the valve, the structure of the valve can be further identified. Such as a safety valve, there are two positioning screws on the valve body, from the channel can be observed on the recoil disc; Seat with a regulating ring is fully open, only the regulating ring or no regulating ring and no recoil plate for micro open. As the gate valve, manually opened, you can distinguish the gate valve is a single or double gate, wedge or parallel type.

How to buy the right valve?

Valves are mechanical devices that control the flow and pressure of fluids in hydraulic or air systems. Valves are an important part of piping systems that carry liquids, gases, steam, sludge, etc.
There are many different types of valves to choose from, each with different characteristics, capacities and uses. Valves are available in different methods of operation: manual, pneumatic, electric, etc.

How do I select a valve?

Before selecting a valve, you need to determine what it will be used for. Will the valve be used to regulate the fluid or to stop the flow of fluid?
Then you need to determine the type of media circulating in the system: is it a gas or a liquid? Is the medium corrosive, chemically neutral, a food product or a medical fluid requiring special sanitary conditions?
When it comes to the operating system of the valve, it is necessary to know whether it is manual or automatic. In the first case, someone must be on site to operate the valve, while in the other case, the valve can be operated remotely, for example from a control station.
Finally, it is important to know how the valve will be integrated into the system and the type of assembly or installation used, especially if welding, bolting through flanges or screwing in is required.
Once these different elements have been identified, you can then focus on the technical characteristics of the installation, in particular the flow and pressure, used to size the valve.

How do I calculate the size of a valve?

In order to calculate the size of the valve, you need to know the parameters related to the operation of the circuit.
Pressure is an important factor that must be taken into account, on the one hand to avoid undersizing the valve, which could lead to problems in terms of leakage or rupture of the valve, and on the other hand to avoid oversizing the valve.
The operating temperature, i.e. the temperature of the circulating medium, and the ambient temperature around the valve body need to be determined. It is important to know the temperature extremes that the valve needs to withstand in order to be able to select the valve that can be used to operate under these conditions, especially the materials used to manufacture the body, shut-off system and seals.
The operating pressure, i.e., the pressure at which the medium will circulate through the valve.
Flow rate and velocity of the fluid. The flow rate and rated velocity are essential elements to help you select the right valve, especially for regulating that flow. The flow coefficient (Kv) is a theoretical value specified by the manufacturer that allows you to calculate the nominal flow rate of the valve. It can be expressed in liters per minute (l/min) or cubic meters per hour (m3/h). The valve manufacturer provides charts to determine this coefficient based on the required flow rate and nominal diameter.
The nominal diameter (DN) of the circuit in which the valve is located. This is essential to avoid oversizing the valve, which may lead to unstable operation of the equipment, or to avoid undersizing, which may lead to a significant pressure drop and rapid valve damage.
Parameters for sizing valves.

• Pressure
• Temperature
• Flow rate
• Diameter

Valve manufacturer YAANG is your best choice

As you can understand, choosing and using the right valve for the right project involves a lot. Not only does the installation of valves require the right skills, but the success of your project also depends on you choosing the right valve. With so much at stake, you need a valve manufacturer like YAANG to provide you with the right valve. Not only will you get the right valve product for the right application, but you will also get the most reasonable valve price.

Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.pilgrimpipeline.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Stainless Steel Valves, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@pilgrimpipeline.com