Pneumatic check valves are two-port valves, with one port allowing fluid to enter and the other allowing for it to exit. Their simple, practical design makes them widely used for many applications in many different industries, including oil and chemical production and manufacturing. They also function automatically, without human control, so they don’t need a valve handle or stem. You’ll most often find pneumatic check valves in gas and fluid lines. Pneumatic flow control valves and pneumatic safety valves are also available..