27

2022

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07

Applications of butterfly valves and gate valves under different working conditions

Author:


Gate valves and butterfly valves both function as switches to regulate flow in pipelines. Of course, there are still methods in the selection process of butterfly valves and gate valves.

    Gate valves and butterfly valves both function as switches to regulate flow in pipelines. Of course, there are still methods in the selection process of butterfly valves and gate valves.

    In the water supply pipeline network, in order to reduce the soil covering depth of pipelines, butterfly valves are generally selected for larger diameter pipes. If the soil covering depth is not much affected, gate valves are selected. However, the price of gate valves of the same specifications is higher than that of butterfly valves. As for the dividing line of caliber, it should be considered on a case-by-case basis. Judging from the use situation in the past ten years, the failure rate of butterfly valves is higher than that of gate valves. Therefore, it is worthy of attention to expand the use scope of gate valves if conditions permit.

     Regarding gate valves, in recent years, many domestic valve manufacturers have developed and imitated soft-sealing gate valves. Compared with traditional wedge-type or parallel double-gate gate valves, this kind of gate valve has the following characteristics:

     The valve body and valve cover of the soft-sealed gate valve are cast by precision casting. They are formed in one step and basically do not need mechanical processing. They do not use sealing copper rings, saving non-ferrous metals.

     There are no pits at the bottom of the soft-sealing gate valve, no accumulation of slag, and the failure rate of the gate valve opening and closing is low.

 

     The soft-sealing rubber-lined valve plate has uniform dimensions and strong interchangeability.

 

     Therefore, soft seal gate valve will be a form that the water supply industry is willing to adopt. At present, the diameter of domestically manufactured soft-sealed gate valves reaches 1500mm, but the diameters produced by most manufacturers are between 80-300mm. There are still many problems in the domestic manufacturing process. The key component of the soft-sealing gate valve is the rubber-lined valve plate. The technical requirements for the rubber-lined valve plate are relatively high, and not all foreign manufacturers can meet them. They are often purchased and assembled from manufacturers with reliable quality.

  The copper nut block of domestic soft-sealed gate valves is embedded and hung above the rubber-lined valve plate. It is similar to the structure of a gate valve. Due to the moving friction of the nut block, the rubber lining of the valve plate can easily peel off. In the soft-sealing gate valve of a foreign company, the copper nut block is embedded in the rubber-lined gate plate to form a whole, which overcomes the above shortcomings, but the concentricity requirement of the combination of the valve cover and the valve body is relatively high.

    However, when opening and closing the soft-sealed gate valve, it must not be closed too far, as long as the water-stopping effect is achieved, otherwise it will not be easy to open or the rubber lining will be peeled off. A certain valve manufacturer uses a torque wrench to control the degree of closure during valve pressure testing. Valve operators of water companies should also follow this opening and closing method.

 

What is the difference between butterfly valve and gate valve?

    According to the functions and uses of gate valves and butterfly valves, gate valves have small flow resistance and good sealing performance. Because the gate valve plate and the flow direction of the medium are at a perpendicular angle, if the gate valve does not open or close the valve plate in place, the erosion of the valve plate by the medium will cause the valve plate to vibrate. , it is easy to damage the gate valve seal.

    Butterfly valve, also called flap valve, is a regulating valve with a simple structure that can be used for switching control of low-pressure pipeline media. The butterfly valve refers to a closing member (valve disc or butterfly plate) that is a disc and rotates around the valve axis to open and close. A kind of valve, the valve can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. It mainly plays the role of cutting and throttling on pipelines. The butterfly valve opening and closing part is a disc-shaped butterfly plate that rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjustment.

    The butterfly plate is driven by the valve stem. If it is rotated 90°, it can complete one opening and closing. By changing the deflection angle of the butterfly plate, the flow rate of the medium can be controlled.

    Operating conditions and media: Butterfly valves are suitable for transporting various corrosive and non-corrosive fluids in engineering systems such as generators, coal gas, natural gas, liquefied petroleum gas, city gas, hot and cold air, chemical smelting, power generation, environmental protection, building water supply and drainage, etc. On the pipeline of the medium, it is used to regulate and cut off the flow of the medium.

    The gate valve is a gate that opens and closes. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully open and fully closed, which varies according to the door parameters, usually 5°, when the medium temperature is not high. is 2°52'. To improve its craftsmanship and compensate for the deviation of the sealing surface angle during the processing, this type of gate is called an elastic gate.

    When the gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, the sealing surface of the gate plate is pressed to the valve seat on the other side by the medium pressure only to ensure the sealing of the sealing surface. This is self-sealing. Most gate valves adopt forced sealing, that is, when the valve is closed, external force must be relied on to force the gate plate to the valve seat to ensure the sealing performance of the sealing surface.

    Movement mode : The gate plate of the gate valve moves linearly with the valve stem, which is also called a rising stem gate valve. Usually there is a trapezoidal thread on the lift rod, and through the nut on the top of the valve and the guide groove on the valve body, the rotational motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. When the valve is opened, when the lift height of the gate plate is equal to 1:1 times of the valve diameter, the fluid channel is completely unobstructed, but during operation, this position cannot be monitored. In actual use, the top of the valve stem is used as a mark, that is, the position that does not open, as its fully open position. In order to consider the locking phenomenon caused by temperature changes, the valve is usually opened to the top position and then retracted 1/2-1 turn as the fully open valve position. Therefore, the fully open position of the valve is determined by the position of the gate plate (i.e. stroke). Some gate valve stem nuts are set on the gate plate, and the rotation of the handwheel drives the valve stem to rotate, thereby lifting the gate plate. This kind of valve is called Rotating rod gate valve or hidden rod gate valve.