Metoda połączenia między zaworem a rurociągiem
The selection of the correct and appropriate connection method between valves and pipelines or equipment will directly affect the probability of pipeline and valve leakage.
The common connection methods for zawory include flange connection, clamp connection, butt welding connection, threaded connection, sleeve connection, clamp connection, self-sealing connection, and other connection forms.
1. Flange connection
Flange connection refers to the installation of flanges on both ends of the valve body, corresponding to the flanges on the pipeline, and fixed in the pipeline through bolts. Flange connection is the most commonly used connection form in valves. There are three types of flanges: raised face (RF), flat face (FF), Male-and-Female face (MF), and so on. According to the shape of the joint surface, it can be further divided into the following types:
- (1) Smooth type: used for valves with low pressure. Processing is relatively convenient
- (2) Concave-convex type: higher working pressure, can be used in hard washers
- (3) Tongue and groove type: available plastic deformation of the gasket, more widely used in corrosive media, the sealing effect is better.
- (4) Trapezoidal groove type: oval metal ring for the gasket, used in the working pressure ≥ 64 kg / cm2 of the valve or high-temperature valves.
- (5) Lens type: the gasket is a lens shape made of metal and used for working pressure ≥ 100 kg / cm2 of high-pressure valves or high-temperature valves.
- (6) O-ring type: this is a newer form of flange connection. It is with the emergence of a variety of rubber O-rings and the development of the sealing effect is more reliable than the general flat gasket.
Precautions for valve connecting flanges
- 1) The flange surfaces of valves and piping should be free from damage, scratches, etc., and kept clean. Especially when using metal gaskets, the groove of the flange should match the gasket and be coated with red lead for research to ensure a good sealing condition.
- 2) The verticality between the flange surface on the piping and the centerline of the piping, as well as the error of the flange bolt hole, should be within the allowable range. The centerline of the valve and piping should be consistent before installation.
- 3) When connecting two flanges, the first step is to ensure that the flange sealing surface and gasket are evenly compressed, thereby ensuring that the flange is connected with equal bolt stress.
- 4) When tightening bolts, use a wrench that matches the nut. When using hydraulic or pneumatic tools for tightening, be careful not to exceed the specified torque.
- 5) The tightening of flanges should avoid uneven force and be tightened in a symmetrical and intersecting direction.
- 6) After flange installation, it is necessary to confirm that all bolts and nuts are tightened evenly.
- 7) The materials of bolts and nuts comply with regulations. After tightening, it is advisable to expose two pitches of the bolt head from the nut.
- 8) To prevent loosening caused by vibration, washers should be used for tightening bolts and nuts. To avoid adhesion between threads during high temperatures, anti-adhesion agents should be applied to the threaded parts during installation.
- 9) For high-temperature valves above 300 ℃, after the temperature rises, tighten the flange connecting bolts, valve cover fastening bolts, pressure seals, and packing gland bolts again.
- 10) When installing valves at low temperatures, they are in a state of atmospheric temperature. Due to the formation of temperature differences, flanges, gaskets, bolts, and nuts shrink, and due to the different materials of these components, their respective linear expansion coefficients also differ, creating an environmental condition that is very prone to leakage. Starting from this objective situation, when tightening bolts at atmospheric temperature, a torque that takes into account the shrinkage factors of various components at low temperatures is used.
2. Clamp connection
The valve is installed between two flanges, and there is usually a positioning hole on the valve body for easy installation and positioning. It is a connection form where the valve and two pipes are directly threaded together with bolts.
3. Welding connection
Butt welding connection: The two ends of the valve body are processed into butt welding grooves according to the welding requirements, corresponding to the pipeline welding groove, and fixed on the pipeline through welding.
Socket welding connection: The two ends of the valve body are processed according to the requirements of socket welding and connected to the pipeline through socket welding.
4. Threaded connection
Thread connection is a simple connection method commonly used for small valves. The valve body is machined according to various thread standards, with two types of internal and external threads. Corresponds to the threads on the pipeline. There are two types of threaded connections:
- 1) Direct sealing: The internal and external threads directly serve as a sealing effect. To ensure that the connection is not leaking, lead oil, hemp, and polytetrafluoroethylene raw tape are often used for filling. Among them, polytetrafluoroethylene raw material belt is widely used day by day. This material has excellent corrosion resistance, excellent sealing effect, and is easy to use and store. When disassembling, it can be completely removed because it is a nonadhesive film, much superior to lead oil and hemp.
- 2) Indirect sealing: The force of thread tightening is transmitted to the gasket between two planes, allowing the gasket to play a sealing role.
There are five main types of commonly used threads: metric regular threads, English standard thread, Thread sealing pipe thread, Nonthreaded sealing pipe threads and American Standard Pipe Thread.
The summary is as follows:
- ① International standards ISO 228/1 and DIN 259 refer to internal and external parallel threads, designated as G or PF (BSP. F);
- ② German standards ISO 7/1, DIN 2999, BS 21, for external conical and internal parallel threads, code BSP.P or RP/PS;
- ③ British standards ISO 7/1, BS 21, internal and external tapered threads, code PT or BSP. Tr or Rc;
- ④ American standard ANSI B21, internal and external tapered threads, code NPT, BSP. F, BSP. P, and BSP. Tr is collectively referred to as BSP threads.
There are five types of American standard pipe threads: general purpose taper pipe thread NPT, straight pipe internal thread NPSC for pipe joints, taper pipe thread NPTR for guide rod connections, straight pipe thread NPSM (free fit mechanical connections) and NPSL (loose fit mechanical connections with lock nuts) for mechanical connections. Belongs to nonthreaded sealing pipe threads (N: American National Standard; P: Pipe; T: Conical
5. Ferrule connection
Ferrule connection has only developed in recent years in China. Its connection and sealing principle is that when the nut is tightened, the ferrule is subjected to pressure, causing its blade to bite into the outer wall of the pipe. The outer cone of the ferrule is then tightly sealed with the inner cone of the joint under pressure, thus reliably preventing leakage, such as instrument valves.
The advantages of this type of connection are:
- 1) Small size, lightweight, simple structure, and easy disassembly and assembly;
- 2) Strong connection force, a wide range of use, able to withstand high pressure (1000 kg/square centimeter), high temperature (650 ℃), and impact vibration;
- 3) Multiple materials can be selected suitable for corrosion prevention;
- 4) Low machining accuracy requirements;
- 5) Convenient for high-altitude installation.
At present, the sleeve connection form has been adopted in some small-diameter valve products in China.
6. Clamp connection
This is a quick connection method that only requires two bolts and is suitable for low-pressure valves that are frequently disassembled. Such as sanitary valves.
7. Inner self-tightening connection
The above various connection forms utilize external forces to counteract medium pressure and achieve sealing. The following is an introduction to the self-tightening connection form using medium pressure. Its sealing ring is installed at the inner cone at a certain angle to the side facing the medium. The medium pressure is transmitted to the inner cone and then to the sealing ring. On the conical surface at a certain angle, two components are generated, one parallel to the centerline of the valve body and facing outward, and the other pressing towards the inner wall of the valve body. The latter component is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. So, this type of connection is suitable for high-pressure valves. It saves a lot of materials and workforce compared to flange connections. It also requires a certain amount of pre-tightening force to ensure reliable use when the pressure inside the valve is not high.
Valves made using the principle of self-sealing are generally high-pressure valves.
8. Other valve connection forms
There are many forms of valve connection, such as some small valves that do not need to be removed and welded together with pipes. Some non-metallic valves use sockets and plug connections, and so on. Valve users should be treated according to their specific needs.
There are many other forms of valve connection, such as some small valves that do not need to be removed and welded together with pipes. Some non-metallic valves use sockets and plug connections, and so on. Valve users should be treated according to their specific needs.
- 1) All connection methods must refer to corresponding standards, and it is necessary to clearly understand the standards required by users to avoid the valve being unable to be installed.
- 2) Usually, large-diameter pipelines are connected to valves using flange connections, while small-sized pipelines are connected to valves using threaded connections.