Connection method of valve

Connection method of valve

Valves are pipeline accessories used to open and close pipelines, control flow direction, and adjust and control the parameters (temperature, pressure and flow) of the conveying medium. According to their functions, they can be divided into shut-off valves, check valves, regulating valves, etc. The connection methods known to valve manufacturers .

Flange connection

Flange connection is a common valve connection method. It places a sealing gasket between two flanges and then bolts the two flanges together to achieve the purpose of sealing and connecting pipes. This connection method has the advantages of easy disassembly, good sealing performance, and high pressure resistance. Therefore, it is widely used in the fields of petroleum, chemical industry, and electric power. Flange connection can be applied to valves of various nominal sizes and nominal pressures, but there are certain restrictions on the use temperature. Under high temperature conditions, the bolts of the flange connection are prone to creep and cause leakage. Generally, flange connection is recommended to be used at a temperature of ≤350 degrees Celsius. According to the shape of the joint surface, it can be divided into the following types:

1. Smooth type: used for valves with low pressure. It is relatively easy to process

2. Concave and convex type: the working pressure is high, and medium-hard gaskets can be used

3. Tongue and groove type: gaskets with large plastic deformation can be used. It is widely used in corrosive media and has a good sealing effect.

4. Trapezoidal groove type: an elliptical metal ring is used as a gasket, which is used for valves with a working pressure of ≥64 kg/cm2, or high-temperature valves.

5. Lens type: The gasket is lens-shaped and made of metal. It is used for high-pressure valves or high-temperature valves with working pressure ≥100 kg/cm2.

6. O-ring type: This is a newer flange connection form, which has developed with the emergence of various rubber O-rings. It is a sealing connection form.

Clamp connection

The clamp connection refers to the pipe flanges on both sides of the valve, which are clamped by bolts to connect the valve to the pipeline system.

Welding connection

Welding connection is a permanent valve connection method, which directly welds the valve and the pipeline together to achieve the purpose of sealing and connecting the pipeline. This connection method has the advantages of good sealing performance, high strength, and not easy to leak, but it is difficult to disassemble and requires professional operation. It is suitable for high-temperature, high-pressure, large-diameter and other pipeline systems. The welding of valves and pipelines is divided into butt welding connection (BW) and socket welding connection (SW). Butt welding connection (BW) can be applied to various sizes, various pressures and high-temperature conditions. Socket welding connection (SW) is generally suitable for valves ≤50.

Threaded connection

Threaded connection is an older valve connection method. It matches the external thread of the valve with the internal thread of the pipe, and then rotates the valve to make it tightly combined. This connection method has the advantages of simple structure and low price, but the sealing performance is poor and it is easy to damage, so it is only suitable for low-pressure and small-diameter pipes. There are two cases:

1. Direct sealing: The internal and external threads directly play a sealing role. In order to ensure that the connection does not leak, lead oil, hemp and polytetrafluoroethylene raw tape are often used for filling; among them, polytetrafluoroethylene raw tape is increasingly widely used; this material has good corrosion resistance, excellent sealing effect, easy to use and store, and can be removed intact when disassembling because it is a non-sticky film, which is much better than lead oil and hemp.

2. Indirect sealing: The force of tightening the thread is transmitted to the gasket between the two planes, allowing the gasket to play a sealing role.

Ferrule connection

The connection and sealing principle of ferrule connection is that when the nut is tightened, the ferrule is subjected to pressure, so that its blade bites into the outer wall of the pipe, and the outer cone of the ferrule is tightly fitted with the inner cone of the joint body under pressure, so it can reliably prevent leakage.

The advantages of this connection form are:

1. Small size, light weight, simple structure, easy disassembly and assembly;

2. Strong connection force, wide range of use, resistant to high pressure (1000 kg/cm2), high temperature (650℃) and impact vibration

3. A variety of materials can be selected, suitable for corrosion protection;

4. The processing accuracy requirement is not high; it is convenient for high-altitude installation.

The ferrule connection form has been adopted in some small-diameter valve products in China.

Clamp connection

Clamp connection is a new type of valve connection method. It is achieved by putting the clamp on the outside of the valve and the pipe, and then tightening the bolts to make the clamp fit tightly with the pipe to achieve the purpose of sealing and connecting the pipe. This is a quick connection method that only requires two bolts and is suitable for low-pressure valves that are frequently disassembled. This connection method has the advantages of easy installation, good sealing performance, and high pressure resistance, so it is widely used in fire protection, water supply and drainage and other fields.

Internal self-tightening connection

The above various connection forms all use external force to offset the medium pressure and achieve sealing. The following introduces the connection form that uses medium pressure for self-tightening. Its sealing ring is installed at the inner cone, which forms a certain angle with the side facing the medium. The medium pressure is transmitted to the inner cone and then to the sealing ring. On the cone surface at a certain angle, two components are generated, one is parallel to the center line of the valve body and outward, and the other is pressed against 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. Therefore, this connection form is suitable for high-pressure valves. It saves a lot of materials and manpower compared to flange connection, but it also requires a certain pre-tightening force so that it can be used reliably when the pressure in the valve is not high. Valves made using the principle of self-tightening 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, which are welded to the pipe; some non-metallic valves use socket-type connections, etc. Valve users should treat them according to specific circumstances.