First, the concept of gate valve:
The gate valve refers to a valve in which the closing member (gate) moves in the vertical direction of the center line of the passage. The gate valve can only be used for full opening and full closing in the pipeline, which cannot be adjusted and throttled. The gate valve is a kind of valve with a wide range of use. Generally, it is used for the cutting device with the diameter of DN ≥ 50mm, and sometimes the cutting device with small diameter also uses the gate valve.
The gate has two sealing faces. The two sealing faces of the most common mode gate valves form a wedge shape. The wedge angle varies with the valve parameters, usually 50, and is 2°52' when the medium temperature is not high. The gate of the wedge gate valve can be made into a whole, called a rigid gate; it can also be made into a gate that can produce a small amount of deformation to improve its processability and compensate for the deviation of the sealing surface angle during the machining process. The board is called a resilient shutter.
When the gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, the sealing surface of the ram is pressed against the valve seat on the other side by the medium pressure to ensure the sealing of the sealing surface, which is self-sealing. Most of the gate valves are forced to seal, that is, when the valve is closed, the external force is forced to press the gate to the valve seat to ensure the sealing of the sealing surface.
The gate of the gate valve moves linearly with the valve stem, which is called the lift gate valve (also called the open gate valve). Usually there is a trapezoidal thread on the lifting rod, and the rotary motion is changed into a linear motion by the nut at the top end of the valve and the guide groove on the valve body, that is, the operating torque is changed to the operating thrust.
When the valve is opened, when the lifting height of the shutter is equal to 1:1 times the diameter of the valve, the passage of the fluid is completely unblocked, but this position cannot be monitored during operation. In actual use, the apex of the valve stem is used as a mark, that is, the position where the valve is opened, as its fully open position. In order to consider the temperature change, the lock phenomenon is usually turned on to the apex position, and then back to 1/2-1 turn as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the shutter (ie stroke).
Second, the advantages of the gate valve:
(1) The fluid resistance is small because the internal medium passage of the gate valve body is straight-through, and the medium does not change its flow direction when flowing through the gate valve, so the fluid resistance is small.
(2) The opening and closing torque is small, and the opening and closing is less laborious. Because the direction of movement of the ram is perpendicular to the flow direction of the medium when the gate valve is opened and closed, the opening and closing of the gate valve is less labor-saving than that of the shut-off valve.
(3) The flow direction of the medium is not restricted. It does not disturb the flow, and does not reduce the pressure medium. It can flow through any direction on both sides of the gate valve, and can achieve the purpose of use. It is more suitable for use in pipelines where the flow direction of the medium may change.
(4) The structural length is short because the gate of the gate valve is vertically placed in the valve body, and the valve flap of the shut-off valve is horizontally placed in the valve body, so the structural length is shorter than the shut-off valve.
(5) Good sealing performance When the sealing surface is fully opened, the sealing surface is less eroded.
(6) When fully open, the sealing surface is less affected by the working medium than the shut-off valve.
(7) The shape is relatively simple, the casting process is good, and the scope of application is wide.
Third, the shortcomings of the gate valve:
(1) The sealing surface is easy to damage the two seals in contact between the gate and the valve seat when opening and closing, and there is relative friction between them, which is easy to damage, affecting the seal and the service life, and the maintenance is difficult.
(2) The opening and closing time is long and the height is large. Because the gate valve must be fully open or closed when it is opened and closed, the ram stroke is large, and the opening requires a certain space. The external dimensions are high and the installation space is large.
(3) Structured complex gate valves generally have two sealing surfaces, which add some processing, grinding and maintenance. There are many difficult parts, making it difficult to manufacture and maintain, and the cost is higher than the stop valve.
Fourth, the diameter of the gate valve shrinkage :
If the diameter of the passage in a valve body is different (often the diameter of the valve seat is smaller than the diameter of the flange joint), it is called the diameter contraction. The shrinkage of the diameter can reduce the size of the parts, reduce the force required for opening and closing, and expand the application range of the parts. But after the path shrinks. The fluid resistance loss increases. In certain operating conditions in certain sectors (such as oil pipelines in the oil sector), valves with reduced diameter are not permitted. This is to reduce the resistance loss of the pipeline, and on the other hand to avoid obstacles to the mechanical cleaning pipeline after the diameter shrinkage.
This article is reproduced from: http://
Sling,Flat Belt Sling,Webbing Sling Belt,Polyester Flat Webbing Sling
Jiangsu Zhongyi Work Rigging Co., Ltd. , https://www.zy-rigging.com