How should the check valve be installed?

What is a check valve?

Check valve is a valve that opens and closes with a circular flap and relies on its own weight and medium pressure to produce action to stop the backflow of the medium. Belong to the automatic valve category, also known as check valve, check valve, backflow valve, or isolation valve. The valve movement is divided into lift and swing types. The lifting check valve and globe valve structure are similar, only they lack a driven valve stem. The medium flows in from the inlet side (lower side) and out from the outlet side (upper side). When the inlet pressure is greater than the sum of the weight of the valve flap and its flow resistance, the valve is opened. Conversely, the valve closes when the medium flows backward. The swing check valve has an oblique and can rotate around the axis of the valve flap, the working principle is similar to the lift check valve. The check valve is often used as the bottom valve of the pumping device and can stop the backflow of water. Check valve and shut-off valve used in combination can play a role in the safety of isolation. The disadvantages are high resistance and poor sealing when closed.

How should the check valve be installed?

Different types of check valve installation methods.

Firstly, swing check valve: swing check valve flap is disc-shaped, rotating movement around the axis of the seat channel, because the valve channel into a streamline, flow resistance than lift check valve is small, suitable for low flow rate and flow does not often change the large diameter occasions, but not for pulsating flow, its sealing performance is not as good as lift type. The swing check valve is divided into single-valve, double-valve, and multi-flap three, these three forms are mainly divided by the valve caliber, the purpose is to prevent the media to stop flowing or backflow, weakening the hydraulic impact.

Second, lift check valve: valve flap along the vertical centerline of the valve body sliding check valve, lift check valve can only be installed in the horizontal pipeline, in the high-pressure small diameter check valve on the valve flap can be used round ball. The lift check valve's body shape and the same as the globe valve (which can be common with the globe valve), so it has a large fluid resistance coefficient. Its structure is similar to the globe valve, and the valve body and valve flap are the same as the globe valve. The upper part of the valve flap and the lower part of the valve cover is processed with guide sleeve Jane, the valve flap guide Jane can be freely lifted in the valve can guide Jane, when the medium flow, the valve flap by the medium thrust open, when the medium stop flowing, the valve flap by the self-hanging landing on the valve seat, to stop the medium backflow. Straight lift check valve media import and export channel direction and seat channel direction perpendicular; vertical lift check valve, the media import, and export channel direction and seat channel direction is the same, the flow resistance is smaller than straight type.

Third, the disc check valve: the valve flap rotates around the pin in the valve seat check valve. Disc check valve structure is simple, and can only be installed in the horizontal pipeline, the seal is poor.

Fourth, pipe-type check valve: the valve flap slides along the centerline of the valve body. The pipe-type check valve is a newly emerged valve, its small size, lighter weight, and good processability, is one of the check valve development directions. However, the fluid resistance coefficient is slightly larger than the swing check valve.

Fifth, the pressure-type check valve: this valve is made for boiler feed water and steam cut off with valve, it has a lift check valve and globe valve or angle valve comprehensive function.

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

Cautions

1, in the piping system, do not let the check valve bear the weight, large check valve should be independently supported so that it is not affected by the pressure generated by the piping system.

2, the installation of the direction of media flow should be consistent with the direction of the arrow marked on the valve body.

3, lift-type vertical flap check valve should be installed in the vertical pipeline.

4, lift type horizontal flap check valve should be installed in the horizontal pipeline.

The working principle of check valve.

Check valve can also be used to provide recharge to the pipeline in which the pressure may rise above the system pressure of the auxiliary system. Check valves can be divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis).

The function of this type of valve is to allow the medium to flow in one direction only and to prevent the flow in the opposite direction. Usually, this valve is automatic work, in one direction of flow of fluid pressure, the valve flap open; fluid flow in the opposite direction, by the fluid pressure and the self-weight of the valve flap combined flap act on the valve seat, thus cutting off the flow.

Among the check valve belonging to this type of valve, it includes the swing check valve and lifts check valve. Swing check valves have a hinge mechanism and a door-like flap that rests freely on an inclined seat surface. To ensure that the flap reaches the right position on the seat surface every time, the flap is designed in the hinge mechanism so that the flap has sufficient swing space and true, full contact with the seat. The valve may be made entirely of metal or maybe inlaid with leather, rubber, or synthetic coverings, depending on the performance requirements. Swing-open check valves, in fully open condition, are virtually unobstructed by fluid pressure, so the pressure drop through the valve is relatively small. Lift check valves have a valve flap that sits on the seat sealing surface on the valve body. This valve is like a globe valve except that the valve can be raised and lowered freely. The fluid pressure causes the valve to lift off the seat sealing surface and the media backflow causes the valve to fall back onto the seat and cut off the flow. Depending on the conditions of use, the flap can be of all-metal construction or in the form of a rubber gasket or rubber ring inlaid on the flap frame. Like the globe valve, the passage of fluid through the lift check valve is narrow, so the pressure drop through the lift check valve is somewhat greater than that of the swing check valve, and the flow rate of the swing check valve is very little restricted.

How to deal with the failure of check valve?

Flap breakage

The causes of valve flap breakage are:

Check valve before and after the media pressure is close to the balance and each other "saw" state, the valve flap often beats with the valve seat, and some brittle materials (such as cast iron, brass, etc.) made of the valve flap is broken.

Prevention is to use the valve flap for the tough material check valve.

Media backflow

The causes of backflow are

① sealing surface damage; ② entrapped impurities.

Repair the sealing surface and clean impurities, you can prevent backflow.

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