What are the working principles and common troubleshooting methods

The working principle of check valve: The function of various types of valves is to allow the medium to flow only in one direction and prevent directional flow. Usually, this type of valve works automatically, and under the pressure of fluid flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the pressure of the fluid and the self weight of the valve disc act on the valve seat, thereby cutting off the flow. Check valves belong to this type of valve, which includes swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve disc like a door that freely rests on the inclined valve seat surface. In order to ensure that the valve disc can reach the appropriate position on the valve seat surface every time, the valve disc is designed in a hinge mechanism so that the valve disc has sufficient swing space and truly and fully contacts the valve seat. The valve disc can be made entirely of metal, or it can be embedded with leather, rubber, or a synthetic cover on top of the metal, depending on the performance requirements. When the swing check valve is fully open, the fluid pressure is almost unobstructed, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except for the valve disc, which can be freely raised and lowered, the rest of this valve is like a globe valve. Fluid pressure lifts the valve disc from the sealing surface of the valve seat, causing the medium to reflux and causing the valve disc to fall back onto the valve seat, cutting off the flow. According to the usage conditions, the valve disc can be made of all metal structure or embedded with rubber, rubber pads or rubber rings on the valve disc frame. Like globe valves, the passage of fluid through lift check valves is also narrow, so the pressure drop through lift check valves is greater than that through swing check valves, and the flow of swing check valves is less restricted. Common faults and troubleshooting methods of check valves include: ① valve disc breakage; ② Medium backflow. The reason for the breakage of the valve disc is that the pressure of the medium before and after the check valve is in a nearly balanced and mutually "sawing" state, and the valve disc often hits the valve seat, causing the valve disc made of some brittle materials (such as cast iron, brass, etc.) to be broken. The preventive measure is to use check valves with resilient valve discs. The reasons for quality backflow include: ① damage to the sealing surface; ② Inclusion of impurities. Repairing the sealing surface and cleaning impurities can prevent backflow.