Normally closed, dual pilot check valve. Cartridge is closed until sufficient pressure is applied on port 1 to reach the bias spring setting, lift the poppet and allow free flow to port 2 . The valve is normally closed from port 2 to 1. When sufficient pressure is applied on Pilot Port , the pilot piston lifts the poppet from its seat and allows flow from port 2 to port 1 (Pil A = 1B. Pil B = 1A). Very limited leakage in the check condition.