Valve Types and Applications–II
Check valves only allow fluids to flow in one direction. The structure of lift check valve is similar to that of stop valve. It uses a ball or piston and is usually supported by a spring. The spring opens under a specified pressure, but closes when the pressure drops, thereby preventing backflow. These valves are generally suitable for high pressure applications. One variant is the stop check valve which also acts as a shut-off valve.
The swing check valve uses a hinged gate, which is usually driven by a spring and closes against the port when the pressure drops. These devices are very effective in low-voltage applications. The tilt disc check valve hinges the gate slightly inward to reduce the pressure required for opening. Butterfly valves or double-door check valves use two semi-circular gates, which are hinged at the centerline of the valve port and open downstream in the flow direction.
Rubber check valves are also available, including designs such as flaps and duckbill varieties. Check valves are used for pumps in gas pipes, air pipes, and wherever fluid flow is required in one direction. They can be miniaturized, made of plastic, and may contain many special features, such as metal valve seats.
Plug valves are used in drain tanks, etc., and usually include threaded devices for opening and closing. They can also be used as low-pressure shut-off valves, usually using a quarter-turn rod. The main specifications include valve type, port connection, valve size and construction materials. Plug valves are used in a range of product applications, including radiators, heaters, water tanks, boilers, laboratory glassware, air systems, water tanks, barrels, etc.