Pneumatic gas shut-off valve

Pneumatic gas shut-off valve

Mainly used in the following situations:

1. Connected with combustible gas leak monitoring instruments, when the instrument detects a combustible gas leak, it automatically and quickly closes the main gas supply valve, cuts off the supply of gas, and promptly prevents the occurrence of malignant accidents.

2. Connected to the extreme temperature and pressure safety controller of the thermal equipment, when the temperature and pressure at the detection point inside the equipment exceed the set limit value, the gas supply valve will automatically and quickly close, stopping the supply of fuel.

3. Connected to the central fire alarm system of high-rise buildings, it automatically cuts off the gas supply inside the building in case of a fire, preventing gas explosions.

4. ZCR gas emergency shut-off valves are installed in the gas supply network of cities or factories, which can be centrally controlled in the central control room and remotely controlled to urgently shut down the pipeline gas supply at the accident site.

Pneumatic gas shut-off valvethe choice

1. Selection of structural types

In terms of cutting effect, angle stroke valves have a simpler structure, more reliable sealing effect, and greater flexibility than straight stroke valves (such as single seat valves, sleeve valves, gate valves, etc.). Representative ones include three eccentric hard seal butterfly valves, ball valves, etc.

2. Selection of sealing surface

1) Face to face sealing:

The common plunger valve core has a sealing surface with a small conical surface of 60 °, and the width of this small conical surface is usually between 0.5mm and 2mm. To seal well, it is necessary to ensure good contact between the two conical surfaces. But in fact, it is always affected by processing errors (such as concentricity, out of roundness, inclination, etc.), and its sealing effect is not very ideal. The leakage rate of such valves is usually 10-4, and after precision grinding, it can reach 10-6, achieving a high sealing level.

2) Spherical seal

By utilizing the spherical rotation of the sphere to be tangent to the fixed small conical surface of the valve, there is a linear contact between them, which is better than the face-to-face sealing effect mentioned above. Ball valves, spherical sealed butterfly valves, etc. are made using this approach, and their leakage rates can reach 10-6 to 10-8. High performance triple eccentric butterfly valves can reach 10-8 or even zero leakage.

3. Selection of sealing materials

1) Soft seal

Except for corrosion-resistant lined valves, general soft sealed valves refer to valves in which one of the valve core or valve seat is sealed with non-metallic materials (mainly polytetrafluoroethylene and rubber, etc.). Soft sealed valves have good sealing effects, but there may be more or less unclean debris (such as welding slag, iron filings, etc.) left during pipeline installation and system cleaning. When they flow through the regulating valve, they are prone to scratching the soft sealed valve seat or core, increasing the leakage rate and poor sealing reliability. Therefore, when choosing a soft seal structure, it is necessary to consider the cleanliness of the medium and strict flushing of the pipeline before operation.

2) Hard seal

Hard sealed and then welded with wear-resistant alloy is a better choice for shut-off valves. This approach considers not only sealing performance but also service life and reliability. Although the factory specifications are only 10-4 to 10-5, which cannot achieve the effect of zero leakage in soft sealing, it is sufficient to meet the requirements of tight cutting. Moreover, it is durable and more cost-effective from an economic perspective.

4．ShanghaiThe reliability of

1) Soft seal, good cutting effect, but not suitable for granular media. Once scratched, leakage will increase sharply. Therefore, when conditions permit, try to choose a hard seal. The hard seal of the "O" type ball valve can reach 10-5, and the three eccentric butterfly valve can achieve zero leakage.

2) Consideration of sealing wear resistance: In addition to selecting hard seals, for cut-off type regulating valves with leakage requirements of 10-4 or more, wear-resistant alloys must be welded to improve the sealing's wear resistance, erosion resistance, and scratch resistance, and to extend the valve's lifespan.

3) The cut-off regulating valve for high-temperature media is assembled at room temperature and operates at high temperatures with temperature changes. Thermal expansion can alter the sealing pressure established during assembly. If it is too tight, the sealing surface will get stuck, and it will cause serious scratches and strains during exercise; If it is too loose or the sealing pressure is insufficient, the leakage will increase sharply in both cases. The solution is to use an elastic valve seat to absorb the difference caused by this change. There are usually three elastic schemes: ① Spring type; ② Thin sheet flexible metal ring; ③ Elastic valve seat that combines rigidity and flexibility. The latter has both flexibility to overcome thermal expansion and rigidity, and is welded with wear-resistant alloys to improve the reliability of the wear-resistant surface.

4) For erosion media containing particles, it is necessary to consider avoiding direct erosion of the valve core by high-speed media.

5) For hard seals, there must be sufficient hardness difference, and materials of the same hardness cannot compromise with each other, which can easily cause scratches and leakage.