Common connection modes of valves
Whether the connection mode between valve and pipeline or equipment is right or not will directly affect the probability of pipeline valve running, emitting, dripping and leaking. Common valve connection methods include: flange connection, clamp connection, butt welding connection, threaded connection, sleeve connection, clamp connection, self sealing connection, etc.
Flange connection is the valve body with flange at both ends, corresponding to the flange on the pipeline, and the flange is fixed by bolts and installed in the pipeline. Flange connection is the most commonly used connection form in valves. Flange has convex surface (RF), plane (FF), convex concave surface (MF), etc. According to the shape of the joint surface, it can be divided into the following types:
- (1) Smooth type: for low pressure valves. The processing is convenient;
- (2) Concave convex type: high working pressure, medium hard washer can be used;
- (3) Mortise and groove type: the washer with large plastic deformation can be used, which is widely used in corrosive media and has good sealing effect;
- (4) Trapezoidal groove type: oval metal ring as gasket, used for valves with working pressure ≥ 64 kg / cm2 or high temperature valves;
- (5) Lens type: washer is lens shape, made of metal. Used for high pressure valve with working pressure ≥ 100 kg / cm2 or high temperature valve;
- (6) O-ring type: This is a relatively new form of flange connection, it is developed with the emergence of various rubber O-rings, and its sealing effect is more reliable than the general flat washer.
The valve is installed in the middle of two flanges. The valve body usually has positioning holes to facilitate installation and positioning. The valve and two end pipes are directly clamped together with bolts.
- (1) Butt welding connection: the two ends of the valve body are processed with paired welding groove according to the requirements of butt welding, corresponding to the pipe welding groove, and fixed on the pipe by welding.
- (2) Socket welding connection: both ends of the valve body are processed according to the requirements of socket welding, and are connected with the pipe through socket welding.
Threaded connection is a simple connection method, commonly used in small valves. The valve body is processed according to each thread standard, including internal thread and external thread. Corresponding to the thread on the pipe. There are two types of threaded connection:
- (1) Direct sealing: internal and external threads directly play a sealing role. In order to ensure that the joint does not leak, it is often filled with lead oil, thread hemp and polytetrafluoroethylene raw material belt; among them, polytetrafluoroethylene raw material belt is widely used; this material has good corrosion resistance, excellent sealing effect, convenient use and preservation, and can be completely removed when dismantling, because it is a non sticky film, which is much better than lead oil and thread hemp.
- (2) Indirect sealing: the force of thread tightening is transmitted to the washer between two planes, which makes the washer play a sealing role.
There are five common types of threads
- (1) Metric ordinary thread;
- (2) Inch ordinary thread;
- (3) Thread sealing pipe thread;
- (4) Non threaded sealing pipe thread;
- (5) American Standard pipe thread.
- ① International standard ISO228 / 1, DIN259, internal and external parallel thread, code g or PF (BSP. F);
- ② German standards ISO7 / 1, DIN2999 and BS21 are external cone thread and internal parallel thread, code BSP. P or RP / PS;
- ③ British standard ISO7 / 1, BS21, internal and external tapered thread, code PT or BSP.TR Or RC;
- ④ American Standard ANSI B21, internal and external tapered thread, code NPT, G (PF), RP (PS), RC (PT) profile angle is 55 °, NPT profile angle is 60 ° BSP. F, BSP. P and BSP.Tr They are collectively referred to as BSP teeth.
There are five kinds of American Standard Pipe Threads: general purpose taper pipe thread NPT, straight pipe internal thread npsc for pipe joint, taper pipe thread NPTR for guide rod connection, straight pipe thread NPSM (free fit mechanical connection) and npsl (loose fit mechanical connection with lock nut). Non threaded sealing pipe thread (n: American national standard; P: pipe; t: cone)
Ferrule connection has been developed in recent years in China. Its connection and sealing principle is that when the nut is tightened, the ferrule is under pressure, which makes its edge bite into the outer wall of the pipe, and the outer conical surface of the ferrule is close to the inner conical surface of the joint under pressure, so it can reliably prevent leakage. Such as instrument valve. The advantages of this connection form are as follows:
- (1) Small size, light weight, simple structure, easy disassembly;
- (2) It can withstand high pressure (1000 kg / cm2), high temperature (650 ℃) and shock vibration;
- (3) A variety of materials can be selected for corrosion protection;
- (4) The requirement of machining accuracy is not high;
- (5) Convenient for high altitude installation.
At present, ferrule connection has been used in some small diameter valve products in China.
This is a quick connection method. It only needs two bolts and is suitable for low pressure valves that are often disassembled. Such as sanitary valve.
Internal self tightening connection
All the above connection forms are sealed by using external force to offset the medium pressure. The following describes the use of medium pressure for self tightening connection.
Its sealing ring is installed at the inner cone and forms a certain angle with the opposite side of the medium. The medium pressure is transmitted to the inner cone and the sealing ring. On the cone with a certain angle, two components are generated, one is parallel to the center line of the valve body and the other is pressed to the inner wall of the valve body. The latter component is the self tightening force. The greater the medium pressure is, the greater the self tightening force is. Therefore, this connection is suitable for high pressure valves.
Compared with flange connection, it saves a lot of materials and manpower, but it also needs a certain preload, so that it can be used reliably when the pressure in the valve is not high. The valve made of self tightening sealing principle is generally high pressure valve.
There are many forms of valve connection, for example, some small valves that do not need to be removed are welded together with pipes; some non-metallic valves use socket connection, etc. Valve users should be treated according to the specific conditions.
- (1) All kinds of connection methods must refer to the corresponding standards, and it is necessary to clearly understand the standards required by users, so as to avoid that the selected valves cannot be installed.
- (2) Generally, large diameter pipeline and valve are connected by flange, while small diameter pipeline and valve are connected by thread.
Source: Network Arrangement – China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, 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 firstname.lastname@example.org
Please notice that you might be interested in the other technical articles we’ve published: