The check valve can also be used to supply the auxiliary system whose 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 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, check valves belong to this type of valve, including swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve flap like a door that rests freely 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 rotation 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 disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the disc can be raised and lowered freely, the rest of the valve is like a shut-off valve. The fluid pressure lifts the disc from the seat sealing surface, and the return of the medium causes the disc to fall back to the seat and cut off the flow. According to the conditions of use, the valve disc can be an all-metal structure, or it can be in the form of a rubber pad or a rubber ring inlaid on the disc holder. Like a 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 rate of the swing check valve is restricted Rarely. 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 is smaller than that of the lift check valve. It is suitable for Low flow rate 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 lifting type. Swing check valves are divided into three types: single valve type, double valve 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. Lift check valve: a check valve whose disc slides along the vertical centerline of the valve body.

The lift check valve can only be installed on a horizontal pipeline. A ball can be used for the disc on the high-pressure small-diameter check valve. The valve body shape of the lift check valve is the same as that of the stop valve, so it has a larger fluid resistance coefficient. 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 guide sleeves. The disc guide can be lifted and lowered freely in the valve guide. When the medium flows downstream, the 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 lift check valve is perpendicular to the direction of the valve seat channel; the vertical lift check valve has the same direction of the medium inlet and outlet channels as the valve seat channel, and its flow resistance is smaller than that of the straight-through type.