Fireproof and antistatic design of ball valve

Fireproof and antistatic design of ball valve

Fireproof and antistatic ball valves are mainly used for gas pipelines with flammable and explosive media. Such as coal gas, natural gas, liquefied petroleum gas and their mixed gases, etc. Ordinary ball valves are used in non-flammable and explosive pipelines, such as water, air, etc. The difference between the two is mainly in the internal structure.

 

Fire protection is divided into three parts:

Fire protection at the ball core and seat (B), fire protection at the flange in the valve body (C), and fire protection at the valve stem (A):

 

The ball core and valve seat are fireproof. 

In the event of a fire, the soft-sealed ball valve can still maintain a certain sealing performance after the valve seat is burned out by high temperature. That is to minimize the occurrence of internal leakage. Although the hard-sealed ball valve can avoid the burning of the seat of the soft-sealed ball valve in case of fire, it is difficult to achieve the sealing performance of the soft-sealed ball valve when the hard-sealed ball valve works normally, and there will be a little internal leakage, especially in the gas pipeline.

The soft sealing valve seat of the fireproof ball valve is embedded in the groove of the valve body. During normal operation, the soft-sealed valve seat remains sealed. When the soft-sealed valve seat burns out, the ball core is pushed by the medium pressure, close to the metal sealing surface of the inner ring, and maintains a hard-sealed state with it, reducing internal leakage. The seat of the ordinary ball valve is directly installed between the valve body and the ball core. After the soft seal seat is burned, it cannot effectively form a metal hard seal.

 

The flange of the ball valve is fireproof. 

Refers to the ball valve body, which is a two-piece or three-piece split structure, and the valve body is combined by bolts. There are O-rings and graphite metal wound gaskets between each section of the valve body to keep the seal. After the O-ring is burnt during a fire, the graphite metal winding gasket still keeps the valve body from leaking or a small amount of leakage. There is also a metal contact seal between the valve bodies. For a one-piece structure ball valve, the valve body is integral, and the valve body basically does not leak.

 

Fire protection at the valve stem.

Refers to the valve stem sealing packing, PTFE is melted at high temperature, the pressure in the valve body will push the valve stem out of the valve body, and the shoulder on the valve stem is blocked by the valve body. And with the help of the pressure in the valve body, the valve stem is pressed tightly to form a seal. At the same time, this bottom-mounted valve stem can prevent the valve stem from being pushed out of the valve body by the medium pressure when the pressure in the middle chamber of the ball valve is abnormally increased, ensuring safety. The filler can use high temperature resistant flexible graphite filler, special filler such as graphite wire combined pressing.

 

Anti-static structure. 

For ball valves with diameter ≤ DN50, conduction can be conducted between the valve stem and the valve body. For ball valves > DN50, it is necessary to ensure that the ball core, valve stem and valve body can conduct electricity. When the power supply voltage does not exceed 12V, the antistatic resistance between the ball core, valve stem and valve body is less than 10Ω.

 

The conductive structure is to drill small holes in two positions on the valve stem, one position is in contact with the valve body, and the other position is in contact with the ball core. A spring and a small metal ball are installed in the small hole. The small metal ball is lifted by the spring to ensure contact with the valve body, valve stem and ball core to form a conductive circuit.

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