Lift check valve is a check valve in which the valve disc moves up and down along the axis of the valve disc sealing surface.
The lift check valve is reliable in action, but has large flow resistance, so it is suitable for occasions with smaller diameters.
The valve disc of the lift check valve works automatically. Generally, there is a conical valve disc pressed on the metal valve seat between the inlet and outlet of the valve. A spring can be added to the valve disc to preload it. When the fluid flows forward, under the action of fluid pressure, the cone-shaped valve disc disengages from the valve seat and the valve opens. During reverse flow, the valve disc falls back to the valve seat under the combined action of its own weight, spring force (if spring preload is provided), and fluid return pressure, and the valve closes.
Lift-type check valves that use metal-to-metal sealing pairs allow a small amount of leakage. They are only suitable for situations where the sealing requirements for fluid backflow are not very strict. They are generally only used in water systems, so they are usually used to prevent condensate from steam traps. Backflow, also used for the outlet of the condensate circulation pump.
The main advantage of the lift check valve is its simple structure. Since the cone disc is the only moving part, the valve is strong and durable and requires little maintenance, and because it is a metal valve seat, it wears very little. The limitation of lift check valves is that they must be installed on horizontal pipes.
The lift check valve, because its valve disc stroke is about 1/3 of the valve disc diameter, greatly reduces the time required for the valve disc to close, thereby effectively reducing the water hammer pressure of the check valve.
The valve disc of the lift check valve can move freely up and down, and the fluid should push the valve disc from bottom to top. When the inlet pressure at the lower part of the valve disc is less than the outlet pressure at the upper part, the valve disc closes by itself due to the dual effects of its own weight and the upper fluid pressure.
Compared with other check valves, lift check valves have the shortest stroke, so only a relatively short stroke is required to open the valve fully.
The operating characteristics of a check valve depend on its design principle. Mainly based on the following aspects:
①The valve with a multi-stage annular valve seat orifice has the smallest stroke
②The disc closure has low inertia
③The guide of the closing member is friction-free
④Choose a spring that matches the operating conditions
In most lift check valves, the valve disc has a guide structure to ensure that the valve disc is coaxial with the valve seat and maintains a seal. However, if impurities enter the guide mechanism of the valve disc, the valve disc may be stuck or close slowly. Therefore, this type of valve disc is only suitable for low-viscosity media, and there are no solid particles.
The disc of the check valve shown in Figure 1 is spherical, and there is a large gap between it and the guide device, so it is very suitable for situations where there is dirt. When the valve closes, the spherical disc rolls into the valve seat to automatically center and obtain an accurate seal.
The check valve shown in Figure 2 is an angle lift check valve with a slow closing device. Its piston cylinder is designed into upper and lower sections, and the two sections have different diameters. The check valve with this structure can close quickly in the first stage, and in the second stage, due to the reduction in the diameter of the piston cylinder, the valve can finally close slowly. The disc head of this check valve is designed into a specific shape. When the valve’s quick closing phase ends, only a small flow channel area is left between the valve disc and the valve seat, thus effectively limiting the valve’s reverse flow speed.
This check valve is specially designed for critical low surge pressures. Low impact pressure is achieved in two ways:
① Set a conical extension end for the closing member, so that when the valve is closed, the medium can be slowly throttled;
② Install a shock absorber on the closing piece, which will take effect at the last moment of closing. The spring used to provide auxiliary closing force has been cancelled, because when the valve is working in this working condition, the breakage of the spring is a danger.
The installation position of the lift check valve must be appropriate to ensure that the gravity of the closing member acts in the direction of valve closing. Since the closing force of the spring-loaded small lift check valve mainly comes from the spring, this type of valve does not need to pay too much attention to the installation orientation. For the above reasons, the valves shown in Figures 1 and 3 can only be installed in horizontal flow situations. In the direction. The valve shown in Figure 2 can only be installed in the vertical upward flow direction. The valve shown in Figure 4 can be installed in a horizontal flow or vertical upward flow orientation.
As shown in Figure 5, the lifting vertical check valve is a check valve in which the valve disc moves up and down along the axis of the valve body passage.
The operating principle of the lifting vertical check valve is exactly the same as that of the lifting check valve. The difference is that its inlet and outlet are in a straight line and can be directly installed on the vertical pipeline without affecting its operating performance. This type of valve should be used for vertical pipelines. This kind of check valve is very suitable.
The spring of the spring lift check valve (Figure 6) is placed at the valve disc. When the thrust on the valve disc generated by the inlet fluid pressure is greater than the spring load, the spring is compressed and the valve disc opens. The greater the fluid pressure, the greater the valve opening. On the contrary, when the fluid pressure drops, the spring stretches and pushes the valve disc to close the valve. Due to the action of the spring, it is helpful to reduce the water hammer pressure generated when the valve opens and closes, the fluid flow path is smooth and the resistance is small. In addition, the discs of small-diameter spring check valves are often made of balls, which has a simpler structure.
Lift check valve is a valve used to control the direction of fluid flow. To ensure its normal operation and extend its service life, routine maintenance is very important.
① Regularly check the appearance of the lift check valve for damage, corrosion, or other problems.
② Clean the inside and outside of the lift check valve regularly to keep its working surface clean and prevent the accumulation of dirt or impurities.
③ Check the sealing performance of the lift check valve. The tightness can be checked by pressure testing the valve. If there is a leakage problem, the seal should be dealt with and replaced in time.
④ Lubricate the moving parts of the lift check valve regularly. Use appropriate lubricants to ensure smooth valve movement.
⑤ Regularly check whether the connecting parts such as the operating rod, nut and coupling of the lift check valve are firm. If it is loose or damaged, it should be repaired or replaced in time.
⑥ Regularly check whether the check function of the lift check valve is normal. This can be checked by operating the valve and observing the direction of fluid flow.
⑦ Regularly check whether the control system of the lift check valve is working properly. If problems are found, repair or replace parts in time.
⑧Regularly record the maintenance status of the lift check valve, including maintenance date, maintenance content, maintenance personnel and other information. This helps track the valve’s maintenance history and provide a reference.
