The selection of the correct and appropriate connection method between the valve and the pipeline or equipment will directly affect the probability of valve leakage, leakage, dripping, or leakage in the pipeline. The common connection methods for valves include flange connection, clamp connection, butt welding connection, threaded connection, sleeve connection, clamp connection, self sealing connection, and other connection forms.

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), raised concave 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) Convex convex type: with high working pressure, medium hard washers can be used;
(3) Tenon groove type: gaskets with large plastic deformation can be used widely in corrosive media, with good sealing effect;
(4) Trapezoidal groove type: using elliptical metal rings as washers, used for valves with a working pressure of ≥ 64 kg/square centimeter, or high-temperature valves;
(5) Lens type: The gasket is in the shape of a lens and is made of metal. For high-pressure valves with a working pressure of ≥ 100 kg/square centimeter, or high-temperature valves;
(6) O-ring type: This is a relatively new type of flange connection that has developed with the emergence of various rubber O-rings. It is more reliable in sealing than ordinary flat washers.

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.

Welded connection

(1) 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.
(2) 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.

Threaded

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 non adhesive 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:

(1) Metric Plain Thread;
(2) English standard thread;
(3) Thread sealing pipe thread;
(4) Non threaded sealing pipe threads;
(5) American Standard Pipe Thread.

The summary is as follows:

① International standards ISO228/1 and DIN259 refer to internal and external parallel threads, designated as G or PF (BSP. F);

② German standards ISO7/1, DIN2999, and BS21 are external cone and internal parallel threads, with the code BSP P or RP/PS;
③ British standards ISO7/1, BS21, internal and external tapered threads, code PT or BSP Tr or Rc;
④ American standard ANSI B21, internal and external tapered threads, codes NPT G (PF), RP (PS), Rc (PT), all with a tooth angle of 55 °, and NPT with a tooth angle of 60 ° BSP F. BSP P and BSP Tr is collectively referred to as BSP teeth.

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 non threaded sealing pipe threads (N: American National Standard; P: Pipe; T: Cone)

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, light weight, simple structure, and easy disassembly and assembly;
(2) Strong connection force, 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.

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.

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 manpower compared to flange connections, but 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.
There are many forms of valve connection, such as some small valves that do not need to be removed, welded together with pipes; Some non-metallic valves use socket and plug connections, and so on. Valve users should be treated according to their specific needs.

Note:

(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.