How to choose and use check valve？

Most check valves are selected based on a qualitative evaluation of the closing speed required for minimum impact pressure or impact-free closing and its closing speed characteristics. This selection method is not necessarily precise, but according to experience, it can produce acceptable results in most use cases.

a. Check valve for incompressible fluids. Check valves for incompressible fluids are selected primarily based on their ability to close without causing unacceptably high surge pressures due to reverse flow causing sudden closure. Selecting this type of valve for use as a low pressure drop valve is usually only considered for the second step.

For this type of check valve, the first step is to evaluate the required closing speed, and the second step is to select the type of check valve that is likely to meet the required closing speed.

b. Check valve for compressive fluids. Although the purpose of selecting a check valve for compressible fluids is to minimize the impact of the valve disc, it can be selected according to a similar selection method for check valves for incompressible fluids. However, for very large pipelines, the The impact pressure of compressible media can also become significant.

If the medium flow fluctuation range is large, the check valve for compressible fluids can use a deceleration device, which works throughout the entire displacement process of the closing member to prevent rapid and continuous hammering on its end.

If the medium flow is continuously stopped and started rapidly, as at the outlet of a compressor, a lift check valve is used, which is combined with a spring-loaded lightweight disc with a short lift.

a. The use of check valves should avoid the following situations:

Excessively high impact pressure caused by valve closing; rapid vibrating action of valve closing parts.

In order to avoid excessive shock pressure caused by closing the valve, the valve must close quickly to prevent the formation of extremely large pressure.

The side flow velocity is the backflow velocity that causes the impact pressure when the valve closes easily. Therefore, the closing speed of the valve should correctly match the attenuation speed of the downstream medium. However, the decay rate of downstream media can vary greatly in liquid systems. For example, if a liquid system uses a set of parallel pumps and one of the pumps suddenly fails, the check valve at the outlet of the failed pump must be closed almost simultaneously. In addition, if the liquid system has only one pump and the pump suddenly fails, or if the delivery pipe is long and the back pressure and pumping head at the outlet end are low, then a check valve with a slower closing speed is better.

If the moving parts of a valve wear out too quickly, it can cause premature valve failure. To prevent this from happening, rapid oscillatory movements of the closing member must be avoided. This ideal situation is not often obtained, for example, if the speed of the downstream medium varies widely, the minimum flow speed is not enough to force the closing member to stop stably. In this case, the movement of the closing member can be suppressed by a damper within a certain range of its operating stroke. If the medium is a pulsating flow, the check valve should be placed as far away from the source of pulsation as possible. Rapid oscillation of the closing member may also be caused by extreme medium disturbance. Wherever this situation exists, the check valve should be placed where the medium disturbance is minimal. Therefore, the first step in using a check valve correctly is to understand the working conditions of the valve.

b. Determination of quick closing check valve. In most practical applications, check valves can only be qualitatively identified for quick closing. The following items can be used as the basis for judgment:

i. The travel of the closing member from the fully open to the closed position should be as short as possible. It can be seen that from the perspective of closing speed, smaller valves have a greater closing speed than valves of the same structure with larger diameters.

ii. The check valve should be closed from the fully open position at the maximum possible downstream medium speed before reverse flow to obtain the maximum closing time.

li. The inertia of the closing member should be as small as possible, but the closing force should be appropriately large to ensure the fastest response to the deceleration of the downstream medium. From the point of view of low inertia, the closure can be considered to be made of lightweight materials, such as aluminum or titanium. In order to achieve both a lightweight material closing element and a high closing force, the closing force generated by the weight of the closing element can be compensated by spring force.

Enhance.

iv. Limiting factors around the closure member that delay the free closing action of the closure member shall be removed.