The Williams Controls WM778 Series 1/8" Inlet Port 150 psi Pressure Protection Valve is designed to protect the air brake system from any accessory failure. This normally closed valve will open when a pressure of 70 psi is reached and will automatically close if pressure drops below 70 psi. It is ideal for use when an auxiliary system is supplied off a primary system and can handle a maximum operating pressure of 150 psi. This valve is also designed to operate in a wide temperature range, from -40 °F to 180 °F. FleetPride is your First Click in Heavy Duty®.