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Application of rubber sealing ring in gate valve field
2021-07-19
Commonly used valves
In water supply and drainage engineering, medium and low pressure valves are widely used, especially low pressure large diameter valves (low pressure valves refer to valves with a nominal pressure of PN ≤ 1.6 MPa), while medium pressure valves (PN 2.5-6.4 MPa) are rare. Gate valves and butterfly valves are the most basic and most widely used leading products. Current status and development of gate valves Gate valves have the longest history of use, and are still used in various countries around the world, especially those below DN300mm, which still occupy a dominant position in all types of valves. The characteristic is that the pressure difference between the front and rear of the valve plate forces the valve plate to press on the valve seat on the right side of the outlet, with good sealing performance, and when the valve plate is fully opened, the pressure loss is small because the valve plate does not remain in the flow path. Used to cut off the medium in the pipeline. The disadvantage is that the operating torque is large, and the valve body and stem are easily damaged during operation, especially large-diameter gate valves. The overall size and weight are also large. The DN1000-diameter gate valve is about 3200mm high and requires four people to operate it. Therefore, the gate valve is generally used in small-diameter, that is, below DN500. The flow resistance of the gate valve is small from fully open to middle opening, and when it is close to fully closed, the flow resistance increases sharply. In a larger range, the flow resistance changes less. When the valve is close to full closure, the flow change is large. Do not use it when the valve is close to closing. At this time, it is difficult to fine-tune the flow. If the valve opening is extremely small, the flow velocity at the opening is extremely fast, which will cause cavitation on the lower side of the gate, accompanied by intense vibration and noise, and long-term throttling operation will often cause the metal of the valve body and gate to occur. Cavitation. If the gate valve is in the middle opening, because the valve plate is supported by the guide rails on both sides, it fits tightly when fully closed. In the middle position, the gap between the valve plate and the guide rail is large and vibration occurs. Therefore, Hongfeng believes that even in areas where the cavitation rate is low, if the valve is throttled for a long time, the guide rail will be deformed, worn or damaged, and because the valve seat is not in full contact, the surface pressure of the contact part is very high. It tends to produce biting corrosion or adhesion, therefore, it is not suitable for flow control. It should also be noted that when the gate valve has a small opening, the flow changes greatly. If the valve is opened and closed in an emergency, it will cause a sharp rise in pressure or negative pressure, especially water hammer when the valve is closed. On the basis of metal sealing gate valves, rubber soft sealing gate valves have been developed in recent years. Its characteristics are: (1) There is no recess at the bottom of the law body, and the fluid passage section is linear, which is not easy to accumulate and foreign matter. (2) The sealing surface of the gate is pressed on the valve body to stop water, and the valve closing torque is small. (3) The sealing performance will not be affected by the bending and stretching of the pipe. (4) The entire valve plate is lined with rubber, which is corrosion-resistant and does not produce rusty water. (5) The valve can replace the sealing material and O-ring while the water is fully opened. (6) The gate has good interchangeability. |
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