They are non-modulating valves which allow free flow through the check valve into the actuator (V2 to C2) and then block the reverse flow until they feel a pilot pressure directly proportional to the load in the pilot line, so that the pilot piston can push the check poppet off its seat. They can lock loads in a leak free mode and they are well suited for many clamping applications or to prevent a negative load from falling down in case of hose failure. They should be fitted as close as possible to the actuator, either flange mounted or connected through metallic pipe.