Introduction to gas valves currently used in China gas industry - part two

Posted: 03/11/2020 04:03:29   Hits: 20
4. Flat gate valve

The flat gate valve is a general-purpose valve that has been used in gas pipelines in recent years. The flow resistance is small at full bore, and the seals on both sides are formed by pressing a Teflon or rubber O-ring on the disc. When the valve is fully closed or fully open, it can't be airless in the middle cavity. It is not convenient for the user to quickly judge whether the valve is closed tightly when repairing. In order to achieve no air in the middle cavity, the opening and closing torque will increase rapidly; some manufacturers make diameter reduction, such as DN200, with inner diameter of only 150mm, which users should pay special attention to. Therefore, the flat gate valve is suitable for applications where the pressure level is low and the nominal diameter is small.

5. Elastic sealed gas gate valve

The elastic sealed gas gate valve is a gas special valve which is different from the flat gate valve. The structural characteristics of the valve are similar to those of the elastic valve seat of the fixed ball valve. The sealing seat on both sides of the disc adopts an elastic floating structure. The sealing surface is always close together during the opening and closing process, and can compensate for the wear and tear of the seal. It is suitable for high pressure level system; the valve can reach airless in the valve chamber when fully open and fully closed. Even if the remaining gas in the valve cavity is released, there is no pressure in the valve cavity. The user can safely construct the pipeline downstream of the valve, which greatly shortens the waiting time for gas outages before the construction.

The connection types of the elastic sealed gas gate valve include flanged type and welded type. The flanged type is the traditional connection method. The welded type can directly weld the valve and the pipe to save the cost of pipe laying. Both valves can be buried directly to avoid unnecessary wells.  It brings convenience to the construction.

When the elastic sealed gas gate valve is fully open, it is like a section of pipeline with the same diameter of the pipeline, and the flow resistance is extremely small; and all the sealing surfaces are hidden and not in contact with the medium. For the artificial coal-based gas, "gas glue" cannot adhere to the sealing surface, and dust and gravel can not be washed on parts for natural gas.

All in all, the elastic sealed gas gate valve is suitable for gas pipelines, especially for underground gas pipelines. From the perspective of foreign investigations, many countries have adopted elastic flat gate valves on natural gas pipelines. Compared with the nominal diameter elastic flat gate valves and ball valves, it has a fireproof function, and the price is about 30% lower than that of the ball valve, and the effect is the same. TRZ series elastic sealed gas gate valve has the disadvantage of high structural height, the height of 4 nominal diameters. Because it is buried underground, the height above the central axis of the pipeline is the same as that of the normal gate valve. The shortcomings are not obvious. More importantly, the height of the lower half is larger than that of the normal gate valve, and the depth of the construction is greater during construction, but generally does not affect the pipeline laying;The height is larger than the usual gate valve, and the depth of burial during construction is greater, but it generally does not affect the pipeline laying;

Introduction to gas valves currently used in China gas industry - gas gate valve

6. Ball valve

The ball valve has been widely used due to its small flow resistance, small structural height, and good sealing performance, and has been rapidly developed in recent years. There are two kinds of ball valves, one is a floating ball valve, that is, the ball can float in the valve cavity, and the ball is stabilized by the sealing seat at both ends. This kind of ball valve can only be used when the nominal diameter is smaller (less than 150mm) or the pressure level is lower (0.8MPa or less). Otherwise, the opening and closing torque will be large, which will bring difficulties to the user.

In the case where the nominal diameter is larger than DN200 or the pressure level is higher, the fixed ball structure is required. When the valve is fully closed, the force exerted on the ball is transmitted to the upper and lower sphere support shafts, greatly reducing the operating torque. The pressure increases and the torque does not increase significantly, making it easy for the operator to use.

The fixed ball valve is specially designed and manufactured for the gas industry. The valve combines the characteristics of various ball valves at home and abroad, and is developed according to China's national conditions. It is suitable for gas long-distance trunk lines and city gas facilities. The valve has obvious features, in addition to the advantages of a general ball valve.

First, the fire resistance. After the high temperature of the fire burns down the PTFE material on the sealing seat, the metal sealing seat and each sealing part can form a metal-to-metal sealing structure to prevent the gas medium from spreading and prevent the disaster from continuing to expand;

Second, anti-static. The static electrode formed by the ball valve during the opening and closing process is easy to ignite the gas, and the ball valve introduces static electricity into the ground to ensure the safety of the device;

Third, position limited and locked. The ball valve is a rotating mechanism, which is easy to cause 360-degree rotation. In addition to the limited position mechanism, it can be locked to prevent accidents caused by operator misoperation or unauthorized operation by non-operators;

Fourth, the ball valve stem seal is designed with an anti-valve-stem-impact device, and uses special O-ring seal, the torque is smaller than the similar ball valve, the operation is easy, and the opening and closing is fast.

 
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