About the use of check valves

Usage of check valve 

1. Swing check valve: The disc of the swing check valve is disc-shaped, and it rotates around the shaft of the valve seat passage. Because the inner passage of the valve is streamlined, the flow resistance ratio increases. 

The drop check valve is small, suitable for low flow velocity and large diameter occasions where the flow does not change frequently, but it is not suitable for pulsating flow, and its sealing performance is not as good as the lift type. Swing check valves are divided into three types, single-leaf type, double-leaf type and multi-half type. These three types are mainly classified according to the valve diameter. The purpose is to prevent the medium from stopping or flowing backwards and weaken the hydraulic shock. 

2.Lifting check valve: a check valve whose disc slides along the vertical centerline of the valve body. The lifting check valve can only be installed on a horizontal pipeline. The disc can be used on a high-pressure small-diameter check valve. . The valve body shape of the lift check valve is the same as that of the stop valve and can be used in common with the stop valve, so its fluid resistance coefficient is relatively large. Its structure is similar to the stop valve, and the valve body and disc are the same as the stop valve. The upper part of the valve flap and the lower part of the bonnet are processed with sound sleeves. The valve disc guide can be freely raised and lowered in the valve guide. When the medium flows downstream, the valve disc opens by the thrust of the medium. It drops down on the valve seat to prevent the medium from flowing backward. The direction of the medium inlet and outlet channel of the straight-through lifting check valve is perpendicular to the direction of the valve seat channel; the vertical lifting check valve has the same direction of the inlet and outlet channels as the valve seat channel, and its flow resistance is smaller than that of the straight-through type.

3. Disc check valve: a check valve in which the disc rotates around the pin shaft in the valve seat. The disc check valve has a simple structure and can only be installed on a horizontal pipeline, with poor sealing performance.

4. In-line check valve: A valve whose disc slides along the centerline of the valve body. The pipeline check valve is a new type of valve. It is small in size and light in weight.

Good manufacturability is one of the development directions of check valves. But the fluid resistance coefficient is slightly larger than that of the swing check valve.

5. Compression check valve: This valve is used as a boiler feed water and steam shut-off valve. It has a comprehensive function of lift check valve and stop valve or angle valve.

In addition, there are some check valves that are not suitable for pump outlet installation, such as bottom valve, spring type, Y-type and other check valves.

The working principle of the check valve

Check valve refers to the valve that automatically opens and closes the disc depending on the flow of the medium itself to prevent the medium from flowing back, also known as check valve, one-way valve, reverse flow valve and back pressure valve. Check valve is a kind of automatic valve. Its main function is to prevent the medium from flowing back, prevent the pump and drive motor from reversing, and to discharge the container medium. Check valves can also be used to supply pipelines for auxiliary systems where the pressure may rise above the system pressure. Check valves can be divided into swing check valves that rotate according to the center of gravity and lift check valves move along the axis. The function of this type of check valve is to only allow the medium to flow in one direction and prevent the flow in the opposite direction. Usually this kind of valve works automatically. Under the action of the fluid pressure flowing in one direction, the valve flap opens; when the fluid flows in the opposite direction, the fluid pressure and the self-coincidence of the valve flap act on the valve seat, thereby cutting off the flow. Among them, the check valve belongs to this type of valve, which includes swing check valve and lift check valve. The swing check valve has a hinge mechanism and a valve disc like a door freely leaning on the inclined valve seat surface. In order to ensure that the valve clack can reach the proper position of the valve seat surface every time, the valve clack is designed in a hinge mechanism so that the valve clack has enough space for turning and makes the valve clack truly and comprehensively contact the valve seat. The valve clack can be made of metal, or inlaid with leather, rubber, or synthetic covering, depending on the performance requirements. When the swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the valve disc can be raised and lowered freely, the valve is like a shut-off valve. The fluid pressure lifts the valve disc from the valve seat sealing surface, and the medium backflow causes the valve disc to fall back to the valve seat and cut off the flow. According to the conditions of use, the valve clack can be an all-metal structure, or it can be in the form of a rubber pad or a rubber ring inlaid on the valve clack frame. Like a globe valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow rate of the swing check valve is affected. The restrictions are few.

Fourth, the structural characteristics of the wafer check valve:

1. The structure length is short, and its structure length is only 1/4~1/8 of the traditional flange check valve.

2.Small size, light weight, and the weight is only 1/4~1/20 of the traditional flange check valve.

3. The valve flap closes quickly and the water hammer pressure is small.

4. Both horizontal pipes or vertical pipes can be used, easy to install.

5. The flow channel is unobstructed and the fluid resistance is small.

6. Sensitive action and good sealing performance.

7. The valve disc has short stroke and small closing impact.

8. The overall structure is simple and compact, and the appearance is beautiful.

9. Long service life and reliable performance.

The role of the check valve in the pump water supply system is to prevent the impact of the high-pressure water backflow on the pump impeller. During the operation of the system, when the pump suddenly stops running for some reason, the pressure in the pump disappears, and the high-pressure water connected to the outlet of the pump will flow back to the pump in the reverse direction. When the pump outlet is equipped with a check valve, it will be closed immediately to prevent the high-pressure water from flowing back to the pump. The function of the check valve in the hot water system is to prevent the hot water from flowing back into the pipeline. If it is a PVC pipe, it is very likely to burn the pipe and even hurt people, especially in the solar water heater system.


Post time: Nov-11-2021