The structure of the valve sealing surface is the key to ensuring reliable sealing of the valve. Generally, it is composed of the valve seat and the gate (valve disc, butterfly plate, ball, etc.). Sealing is achieved by the close contact of two or more precisely processed and ground sealing surfaces on the valve seat, gate (or valve disc, butterfly plate, ball) or the plastic deformation produced after sealing pressure. The basic requirements for the sealing surface are: ① Resistant to corrosion by the medium passing through; ② Excellent wear resistance and scratch resistance; ③ Ensure reliable sealing under the required working conditions; ④ Good processability; ⑤ It is convenient for assembly and maintenance.

Forms of Sealing Surfaces

1. The two contact surfaces of a flat seal are flat. Flat seals have the following advantages: ① They are convenient for processing and repair; When used on a stop valve, there is no friction at the moment of opening and closing. The disadvantages are: ① When used on a stop valve, the axial force on the valve stem is relatively large; When used on gate valves, the possibility of the sealing surface being scratched at the moment of opening and closing is relatively high, so scratch-resistant materials should be selected.

2. The two contact surfaces of the conical surface seal are conical surfaces. The advantages of conical surface seals are as follows: ① Conical surface seals form a relatively large sealing force and have good sealing performance; ② Compared with planar seals, the axial force is relatively small. It is widely adopted in high-pressure and small-diameter valves. The disadvantages are: ① It is relatively difficult to process and repair; When used on a stop valve, there is a friction phenomenon caused by relative motion at the moment of closing. Needle valves also belong to one type of conical seals.

3. Spherical seal: One of the two contact surfaces to be sealed is a spherical surface. This is a line contact sealing surface with a large sealing specific pressure and good sealing performance. It is widely used in ball valves, butterfly valves and some small-diameter stop valves, but it is more difficult to maintain.

4. The knife-shaped seal has one of the two contact surfaces of the sealing surface in a knife-edge shape. This is a type of seal that lies between line seals and plane seals and is widely used in vacuum valves, solenoid valves or other conditions where the sealing force is not large.

Formation of the Sealing Surface

The sealing surface can be directly processed on the body (valve body, valve disc, gate), for instance, if the valve body, valve disc, and gate are all made of austenitic stainless steel, austenitic-ferritic duplex stainless steel, Monel alloy, lnconel alloy, Hastelloy, etc., or carbon steel valves that do not belong to the stainless steel category but are used for oil media (without corrosion and not prone to rust) It can be directly formed on the main body without an additional sealing ring.

2. After being processed into sealing rings with appropriate materials, they are respectively installed on the valve body, valve seat and gate (valve disc), and then processed into sealing surfaces. The installation methods are diverse, such as pressing, threaded connection, welding, brazing, etc. The sealing surfaces formed by such methods are suitable for all kinds of valves and various sealing surface materials, and are widely used.

3. The sealing surface is formed by conical welding or spray welding of stainless steel (including the transition method with alloying elements) or hard alloy on the valve body (valve seat) and the gate (valve disc), which ensures the strength of the connection between the sealing material and the base material. Therefore, it is increasingly adopted in steel valves.

4. The sealing surface is formed by heat treatment methods such as nitriding, boronizing and chromiizing in the base metal. This is a new process method with low cost and good sealing performance, but it is relatively difficult to repair after wear.

5. The electroless plating method is adopted to deposit nickel-phosphorus (ENP) on the base material to enhance surface hardness and corrosion resistance, such as the ball of a ball valve. This is a new process that has been studied and adopted in recent years.

6. By using the spray plating method, a layer of appropriate sealing material, such as plastic, is coated on the base metal. The sealing surface formed through processing is suitable for working conditions with relatively low nominal pressure and temperatures below 120℃.

7. On the surface of the processed base material, tungsten carbide (WC) or hard alloy powder is sprayed at supersonic speed. After spraying, it is directly ground or ground to form a sealing surface, with a surface hardness of over 65HRC. The bonding strength between the spray coating and the base material can reach 70PAa, making it suitable for the valve seats and balls of metal-sealed ball valves.

8. Nickel-based nano-powder is thermally sprayed on the base material by the carbonyl method. After spraying, mechanical processing is carried out to obtain a sealing surface that is resistant to erosion and wear. The hardness of the sealing surface can reach over 50HRC, which is suitable for the surface of the valve seat and disc of high-pressure Angle stop valves.

The fastening form of the sealing surface

There are many forms of fastening for the sealing surface, mainly determined by the nature of the medium used (pressure, temperature, corrosiveness, etc.), the material of the sealing ring and the material of the shell. The basic requirements for the fastening of the sealing ring are: the mating surface has good sealing performance (the medium will not leak between the mating surfaces), it is convenient for processing, easy to maintain, reliable in connection and durable.