Pneumatic Check Valve 1/4" FPT x 1/4" FPT. Prevent high air pressure from traveling back from the receiver to the pump. It is a one way check valve which is ideal for blocking back-flow of air. It features two female NPT threads for in-line applications. Interstate Pneumatics VC440 In-Line Check Valve 1/4" FPT x 1/4" FPT. Prevent high air pressure from traveling back from the receiver to the pump. It is a one way check valve which is ideal for blocking back-flow of air. It features two female NPT threads for in-line applications.