Check valve refers to the valve that automatically opens and closes the valve disc depending on the flow of the medium itself to prevent the backflow of the medium. It is also known as check valve, one-way valve, reverse flow valve and back pressure valve. The check valve belongs to an automatic valve. Its main function is to prevent the backflow of medium, the reverse rotation of pump and driving motor, and the discharge of container medium.
Working principle of check valve
1. In order to prevent the reverse flow of medium, check valves shall be installed on equipment, devices and pipelines;
2. Check valves are generally suitable for clean media, not for media containing solid particles and high viscosity;
3. Generally, horizontal lifting check valve shall be selected on horizontal pipeline with nominal diameter of 50mm;
4. Straight through lifting check valve can only be installed in horizontal pipeline;
5. For the inlet pipeline of the pump, the bottom valve should be selected. Generally, the bottom valve is only installed on the vertical pipeline at the pump inlet, and the medium flows from bottom to top;
6. The lifting type has better sealing performance and large fluid resistance than the swing type. The horizontal type should be installed on the horizontal pipeline and the vertical type on the vertical pipeline;
7. The installation position of swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines. If installed on vertical pipelines, the medium flow direction should be from bottom to top;
8. The swing check valve should not be made into a small-diameter valve, but can be made into a very high working pressure. The nominal pressure can reach 42MPa, and the nominal diameter can also be very large, which can reach more than 2000mm. According to the different materials of the shell and seal, it can be applicable to any working medium and any working temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of medium is – 196-800 ℃;
9. Swing check valve is suitable for low pressure and large diameter, and the installation occasion is limited;
10. The installation position of butterfly check valve is not limited. It can be installed on horizontal pipeline or vertical or inclined pipeline;
Structural principle of check valve
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 seat of the lift check valve is located on the sealing surface of the valve body. Except that the valve disc can rise and fall freely, the rest of the valve is like a stop valve. The fluid pressure lifts the valve disc from the sealing surface of the valve seat, and the medium backflow causes the valve disc to fall back to the valve seat and cut off the flow. According to the service conditions, the valve disc can be of all metal structure or inlaid with rubber pad or rubber ring on the valve disc frame. Like the stop 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 of the swing check valve is rarely limited.
1、 Swing check valve: the disc of the swing check valve is in the shape of a disc and rotates around the rotating shaft of the valve seat channel. Because the channel in the valve is streamlined and the flow resistance is smaller than that of the lift check valve, it is suitable for large-diameter occasions with low flow rate and infrequent flow change, but it is not suitable for pulsating flow, and its sealing performance is not as good as that of the lift check valve. Swing check valve is divided into single disc type, double disc type and multi half type. These three forms are mainly divided according to the valve diameter, in order to prevent the hydraulic impact from being weakened when the medium stops flowing or flows back.
2、 Lift check valve: a check valve whose valve disc slides along the vertical centerline of the valve body. The lift check valve can only be installed on the horizontal pipeline. On the high-pressure small-diameter check valve, the valve disc can adopt a ball. The body shape of the lift check valve is the same as that of the stop valve (which can be used with the stop valve), so its fluid resistance coefficient is 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 disc and the lower part of the valve cover are processed with a guide sleeve. The valve disc guide sleeve can rise and fall freely in the valve cap guide sleeve. When the medium flows downstream, the valve disc opens by the thrust of the medium. When the medium stops flowing, the valve disc falls on the valve seat vertically to prevent the reverse flow of the medium. The direction of medium inlet and outlet channel of straight through lifting check valve is perpendicular to the direction of valve seat channel; The direction of medium inlet and outlet channel of vertical lifting check valve is the same as that of valve seat channel, and its flow resistance is smaller than that of straight through check valve.
3、 Butterfly check valve: a check valve whose disc rotates around the pin shaft in the valve seat. Disc check valve has simple structure and can only be installed on horizontal pipeline with poor sealing performance.
4、 Pipeline check valve: a valve whose disc slides along the center line of the valve body. Pipeline check valve is a new valve. It has small volume, light weight and good processing technology. It is one of the development directions of check valve. However, the fluid resistance coefficient is slightly larger than that of swing check valve.
5、 Compression check valve: This valve is used as a boiler feed water and steam shut-off valve. It has the comprehensive function of lifting check valve, 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, etc.
Post time: May-09-2022