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Dungong Valve (Shanghai) Co., Ltd.

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Precautions and sealing principles in check valve operation

2020-11-18 10:39:56
Times

The operation method of Shanghai electric gate valve and check valve should avoid the following situations:

1. Excessively high impact pressure caused by the closing of the check valve.

2. The valve closing parts quickly oscillate.

The disc of the spherical check valve is a ball covered with rubber or engineering plastic, so its sealing performance is reliable. According to the size of the nominal diameter of the ball check valve, there are single ball and multi ball. The sealing principle is: when the pump is turned on, the medium pressure generated by the forward flow of the medium pushes the ball to move, and it leaves the sealing surface of the valve seat along the guide, the check valve opens, and the medium passes; when the pump is stopped, the medium flows in the reverse direction. The pressure pushes the ball to roll along the guide pin to the sealing surface of the valve seat and closes the check valve. Depending on the pressure of the working medium, a certain sealing specific pressure is generated between the valve disc and the sealing surface of the valve seat to ensure the sealing of the check valve to prevent The purpose of the medium flow back. Since the contact surface between the ball disc of the spherical check valve and the sealing surface of the valve seat is relatively narrow, under the same medium working pressure, the line seal has a higher sealing pressure than the surface seal, so the seal is reliable. However, the seal sphere of the spherical check valve is covered with rubber or engineering plastics, so the working temperature is limited by the material. Generally, the working temperature of the medium is below 150 degrees.

上海电动闸阀

Electric gate valve

In order to avoid the excessively high impact pressure caused by closing the check valve, the valve must be closed quickly to prevent the formation of a great backflow velocity. The reverse flow speed is the cause of the impact pressure, so the closing speed of the check valve should be correctly matched with the decay speed of the downstream medium. However, the decay rate of downstream media may vary greatly in liquid systems. For example, if a group of associated pumps are used in a liquid system and one of them suddenly fails, the check valve at the outlet of the failed pump must be closed almost simultaneously. In addition, if there is only one pump in the liquid system, and the pump suddenly fails, if the delivery pipe is longer, and the back pressure and pumping pressure at the outlet end are low, it is better to close the check valve with a lower speed. If the moving parts of the check valve wear out too quickly, it will cause the valve to fail prematurely. In order to prevent this from happening, it is necessary to prevent the closing member from producing rapid oscillations. This rapid oscillating action of the closing member can be avoided by selecting a valve for a medium speed that forces the closing member to stably deal with the stop of the medium flow. This ideal situation is not always available. For example, if the velocity of the downstream medium varies widely, the minimum flow velocity is not enough to force the closure to stop stably. In this case, the movement of the closing member can be controlled with a damper within a certain range of its action stroke. If the medium is pulsating flow, the check valve should be placed as far away as possible from the source of pulsation. The rapid oscillation of the closing member may also be caused by extreme media disturbance. Where these conditions exist, the check valve should be placed where the media disturbance is minimal.

Therefore, to choose a check valve is first to grasp the working conditions of the check valve.


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