Spring Check Valves

A spring check valve refers to a valve whose opening and closing part is a circular valve disc and acts by its weight and medium pressure to block the backflow of the medium. It is an automatic valve and is also known as a one-way valve or isolation valve. The disc movement of a spring check valve is divided into lift types and swing types. The lift check valve has a similar structure to the globe valve, except that it lacks the valve stem to drive the disc. The medium flows from the inlet port (the lower side) and comes out from the outlet port (the upper side). When the inlet pressure is greater than the sum of disc weight and its flow resistance, the valve is opened. Conversely, the valve is closed when the medium flows backward. The swing check valve has an oblique disc that can rotate around the axis, and its working principle is similar to that of the lift check valve. The check valve is often used as the bottom valve of the pumping device to prevent the backflow of water. The combination of a check valve and globe valve can play the role of safe isolation. The disadvantage is that the resistance is great, and the sealing is poor when the valve is closed.
 
Working principles of spring check valves
Spring check valves can also be used on pipelines that supply auxiliary systems where the pressure may rise above system pressure. Check valves can be mainly divided into swing check valves (rotating according to the center of gravity) and lifting check valves (moving along the axis). The function of this type of 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 fluid pressure flowing in one direction, the valve disc opens; when the fluid flows in the opposite direction, the valve seat is acted on by the fluid pressure and the self-weight of the valve disc to cut off the flow.
 
Among them, the check valve belongs to this type of valve, which includes swing check valves and lift check valves. The swing check valve has a hinge mechanism, and a door-like disc freely leans on the inclined seat surface. To ensure that the valve disc can reach the proper position of the seat surface every time, the valve disc is designed in the hinge mechanism, so that the valve disc has enough swing space, making the valve disc truly and comprehensively in contact with the valve seat. The disc can be made of metal, or it can be inlaid with leather, rubber, or a synthetic cover on the metal, depending on the requirements for performance. When the swing check valve is fully open, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The 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 rise and fall freely, the rest of the valve is like a globe valve. The fluid pressure makes the valve disc lift from the sealing surface of the valve seat, and the backflow of the medium causes the valve disc to fall back to the valve seat and cut off the flow. According to the conditions of use, the disc can be of all-metal structure, or in the form of a rubber pad or rubber ring inlaid on the disc frame. Like the globe valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is greater than that of the swing check valve, and the flow rate of the swing check valve is limited. 
 
Installing swing check valves
The disc of the swing check valve is disc-shaped and rotates around the shaft of the valve seat channel. Because the channel in the valve is streamlined, the flow resistance is smaller than that of the lift check valve. It is suitable for large-diameter occasions with low flow rates and infrequent flow changes, but it is not suitable for pulsating flow; its sealing performance is not as good as that of the lifting type. Swing check valves are divided into three types, that is, single-disc types, double-disc types and multi-disc types. These three types are mainly divided according to the valve diameters. The purpose is to prevent the hydraulic impact when the medium stops flowing or reverses.
 
Installing lifting check valves
A lifting check valve can only be installed on horizontal pipes. The disc can be adopted for high-pressure small-diameter check valves. The valve body shape of the lift check valve is the same as that of the globe valve, so its fluid resistance coefficient is relatively great. Its structure is similar to the globe valve, and the valve body and disc are the same as the globe valve. The upper part of the valve disc and the lower part of the bonnet are processed with guide sleeves. The guide rib of the valve disc can be lifted and lowered freely in the valve. When the medium flows, the valve disc is opened by the thrust of the medium. When the flow stops, the valve disc falls on the valve seat by its weight. The direction of the medium inlet and outlet channels of the straight-through lift check valve is perpendicular to that of the valve seat channel; the direction of the medium inlet and outlet channels of the vertical lift check valve is the same as the direction of the valve seat channel, and its flow resistance is smaller than that of the straight-through type.
 
Installing disc check valves
A disc check valve is a valve whose disc rotates around the pin shaft in the valve seat. The disc check valve has a simple structure and can only be installed on horizontal pipelines with poor sealing performance.
 
Installing pipeline check valves
A pipeline check valve is a valve whose disc slides along the centerline of the valve body. It is a new type of valve. It has small sizes, light weight and good processing technology. It is one of the development directions of a check valve. However, the fluid resistance coefficient is slightly greater than that of the swing check valve.
 
Installing compression check valves
These valves are used as boiler feed water and steam cut-off valve. It has the comprehensive functions of lift check valves, globe valves and angle valves.
 
In addition, some check valves are not suitable for installation at the pump outlet, such as bottom valves, spring valves, Y types, etc.
 
Matters needing attention in the use of spring check valves
1. Do not allow the check valve to bear weight in the pipeline system. Large check valves should be independently supported so that they are not affected by the pressure generated by the pipeline system.
2. When installing, pay attention to that the direction of medium flow should be consistent with that of the arrow marked on the valve body.
3. The lifting vertical disc check valve should be installed on the vertical pipeline.
4. The lift-type horizontal disc check valve should be installed on the horizontal pipeline.
 
How to deal with the failure of the spring check valve?
Broken discs
The reason for the broken disc is that the pressure of the medium before and after the check valve is close to balance. The valve disc hits the valve seat. The disc made of some brittle materials such as cast iron and brass can be easily broken. The preventive method is to use a check valve with a tough material as the disc.
 
Flow back of the medium 
The reasons for the backflow of the medium are: ①The sealing surface is damaged. ②Impurities are trapped.
Measures: Backflow can be prevented by repairing the sealing surface and cleaning impurities.