1. Basic functions and types of check valves

A check valve, also known as a check valve, one-way valve, reverse flow valve, and back pressure valve, is a type of valve that automatically opens and closes based on the activity of the medium itself. Its core function is to prevent medium backflow, protect the pump and drive motor from reverse effects, and also achieve the release of container medium. In addition, check valves are widely used in pipelines to supply auxiliary systems that may exceed system pressure. According to its working principle, check valves can be divided into two types: swing type (rotating according to the center of gravity) and lift type (moving along the axis). The design feature of this type of valve is to only allow the medium to flow in one direction and effectively prevent its reverse flow.

Usually, these types of valves will actively open or close based on the direction of fluid activity. When the fluid moves in a single direction, the valve disc will be affected by the fluid pressure and open; When the direction of fluid activity is opposite, the fluid pressure and the self weight of the valve disc will work together, causing the valve disc to tightly adhere to the valve seat, thereby cutting off fluid activity. The check valve is a typical application of this principle, which mainly includes two types: rotary and lifting.

2. Swing and lift check valves

Characteristics of rotary check valve

The unique feature of the swing check valve lies in its hinge mechanism and gate shaped valve disc design. The valve disc can freely rest on the inclined valve seat surface, ensuring that it can accurately reach the appropriate position every time. This design not only provides sufficient swing space, but also allows the valve disc to fully contact the valve seat, ensuring a sealing effect. The material selection of the valve disc is also quite flexible, and it can be decided whether to use all metal manufacturing or embed leather, rubber and other materials on the metal according to actual usage needs. In the fully open state, the impact of the swing check valve on fluid pressure can be almost negligible, so the pressure drop through the valve is relatively small.

◆ Features of lift check valve

On the other hand, the valve disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. This design allows fluid pressure to push the valve disc up from the sealing surface of the valve seat, and when the medium flows back, the valve disc will fall back onto the valve seat due to its own weight, thereby cutting off fluid activity. Similarly, the structure of the valve disc can also be made of all metal, or by embedding rubber pads or rubber rings on the valve disc frame. Due to the relatively narrow passage of the fluid through the lift check valve, the pressure drop through the valve will be slightly greater than that of the swing check valve, but the flow is relatively less restricted.

3. Check valve experiment and precautions

Experimental conditions and methods

Test condition of check valve: In the lift check valve, the axis of the valve disc is kept straight from the horizontal direction; For rotary check valves, the channel axis and valve disc axis are approximately parallel to the horizontal line. In the strength experiment, we introduce the experimental medium to the predetermined pressure through the inlet end and seal the other end to check the valve body and valve cover to ensure no leakage. For the sealing test, the experimental medium is introduced from the outlet end, and the sealing surface, packing, and gasket are carefully inspected at the inlet end. It is also required that there is no leakage to be considered qualified.