Check valves, also known as one-way valves or non-return valves, are designed to prevent backflow of media in pipelines. The bottom valve of a pump's suction is also a type of check valve.

The valves are categorized structurally into three types: lift check valves, swing check valves, and butterfly check valves. The lift check valves come in two orientations: vertical and horizontal. Check valves are further divided into single-leaf, double-leaf, and multi-leaf designs. Butterfly check valves are available in straight-through models. In terms of connection types, these valves can be threaded, flanged, or welded.

In hot water heating systems, to reduce the impact of water hammer during emergency shutdowns, a pressure relief bypass pipe equipped with a check valve can be installed between the pressure and suction pipes of the circulating pump. During pump operation, the check valve remains closed due to the higher water pressure on the discharge side compared to the suction side. Upon an abrupt shutdown, the pressure on the discharge side of the pump drops sharply, while the pressure on the suction side increases significantly. Under this pressure difference, the water in the suction side pipeline of the circulating pump is forced through the check valve to the discharge side network, thereby lessening the increase in pressure on the suction side network; reducing and preventing the hazards of water hammer. The check valves installed on the pressure relief bypass pipe should be selected for their low resistance and ease of operation. A larger diameter of the pressure relief bypass pipe is more effective in reducing water hammer. The diameter can be determined economically by performing transient calculations based on the specified pressure limits.

The check valve disc can freely rise and fall, while the rest of the part is like a gate valve, with fluid pressure lifting the disc from the sealing surface of the valve seat. The medium backflow causes the disc to fall back onto the valve seat, thereby cutting off the flow. The usage conditions allow the disc to be a full metal structure or to have a rubber pad or rubber ring embedded in the disc bracket. Like a gate valve, the check valve's lifting passage is narrow, and the pressure drop of a micro-resistance slow-closing check valve is greater than that of a swing check valve, with the flow rate of a swing check valve being limited very little.