Parker blocking valves are designed for cutting the supply and exhaust of a cylinder and preventing damage to personnel and equipment in an event of pressure loss. These single acting spring return valves require a pneumatic pilot signal to keep the passage open for free flow of air stream, gas or a liquid. However, in the absence of this pilot signal, the internal spring closes the blocking valve bubble to prevent any potential damage. They are positioned at each end of the cylinder to freeze the location and prevent unwanted gravity-induced motion during the shutdown. These valves have a pressure rating of 150 PSI and are perfect for tool protection, horizontal indexing or intersection stop applications. Choose from a wide range of these blocking valves, available in 1/2, 1/8, 3/8 and 1/4 inch port sizes.