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Structural features of china DIN3352 F4 resilient seated gate valve

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Structural features of china DIN3352 F4 resilient seated gate valve

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Time
2021/06/08
The stem of china DIN3352 F4 resilient seated gate valve adopts stem seal structure, and the stem seal adopts three O-rings structure. The third O-ring can reduce the pressure at the gland, and at the same time, it can realize the replacement of the upper two seal rings when the pipeline has medium pressure. Compared with the stuffing box structure, the O-ring sealing structure can effectively reduce the opening and closing torque of the valve.

The stem of china DIN3352 F4 resilient seated gate valve adopts stem seal structure, and the stem seal adopts three O-rings structure. The third O-ring can reduce the pressure at the gland, and at the same time, it can realize the replacement of the upper two seal rings when the pipeline has medium pressure. Compared with the stuffing box structure, the O-ring sealing structure can effectively reduce the opening and closing torque of the valve.

Gate structure of china DIN3352 F4 resilient seated gate valve:There are mainly two kinds of ram seal: cut-off type and wedge type. The cut-off type is widely used in the specifications above djv250. Its characteristic is that the side rubber does not play a sealing role. During the closing process, the side rubber of the ram does not squeeze and deform with the inner wall of the valve body. Only when the rubber is finally closed, it deforms and seals. In the process of closing, the torque is small and the requirements for valve manufacturing are high, especially for the casting process of valve sealing surface, which requires high dimensional accuracy and surface roughness. Wedge type is widely used in the specifications below DN250. Its characteristic is that the side rubber plays a sealing role. During the closing process, the inner wall of the rubber valve body on the side of the ram is extruded and deformed, thus forming a seal. It is recommended to use the stuffing box structure, especially in the directly buried gate valve. It is not allowed to use it because the stuffing box structure needs to be lubricated by outward seepage, Asbestos and other materials shall not be used for valve stem sealing. The O-ring seal structure requires higher machining accuracy and surface roughness accuracy than the packing structure, otherwise the O-ring will be cut. The trapezoidal thread of valve stem should be extruded, with high surface hardness and low friction coefficient. The requirements for rubber material, process and performance must meet the standard specifications, otherwise rubber aging will affect the service life of the valve. NBR (nitrile rubber) or EPDM (ethylene propylene diene monomer) is recommended. The valve stem limit is designed as step type, which is convenient for the assembly of the third sealing ring, and can also be designed as combined type.

It is recommended to adopt packing box structure, especially in direct buried gate valve, it is not allowed to use, because the packing box structure needs to be lubricated with outward water seepage, and the valve stem seal cannot use asbestos containing materials. The machining accuracy and surface roughness precision of the 0-ring seal structure are higher than that of the packing structure, otherwise the case of cutting 0-ring will occur. The trapezoidal thread of valve stem should be extruded, with high surface hardness and low friction coefficient. The requirements for rubber material, process and performance must conform to the standard specifications, otherwise the aging of rubber will affect the valve life. NBR (NBR) or EPDM (EPDM) is recommended. The valve stem limit is designed as step type, which is convenient for the assembly of the third sealing ring, and can also be designed as combined type.  Four common china DIN3352 F4 resilient seated gate valve

 stem sealing structures that meet the standards. The structure is complex, the nut and ram have no adjustment clearance, and the ram manufacturing process is complex. At the same time, the processing and assembly accuracy of each part is required high, but the structure is reliable, and there is no rubber layer wear.

The thickness of the rubber covered by the china DIN3352 F4 resilient seated gate valve ram is generally not less than 2mm, and the thickness of the sealing surface is generally about 6 ~ 9mm for the larger nominal size. The sealing compression ratio should be controlled at about 15% - 25%. After coating, there should be no bubble, crack, scar, wound, cast iron exposure and other defects.

NBR (acrylonitrile butadiene rubber) is widely used in most of the china DIN3352 F4 resilient seated gate valve ram coated rubber in China, but according to the Australian standard as 2638.2 "gate valves for waterways - Part II elastic seat seals", the ram coated rubber material is EPDM (ethylene propylene diene monomer). It is suggested that the hardness of rubber should be 65-75irhd, and the hardness of rubber can be increased appropriately when the pressure exceeds 1.6Mpa. EPDM has good aging resistance, excellent compression resistance, and can prevent the damage of organic matter, ozone and ultraviolet light. The rubber rings of water supply pipes in European countries have all been made of EPDM.

Whether it is a rising stem or a non rising stem china DIN3352 F4 resilient seated gate valve, the gate will be affected by the static pressure of the medium in the sealing process, and due to the existence of the assembly clearance of the valve stem and other parts, the gate will move towards the medium flow direction, and the outlet sealing surface will be further compressed. At the same time, the compression of the inlet wedge is reduced by the same amount, which weakens or even loses the sealing condition, forming a forced sealing of one side wedge.