The blocking valves are used to maintain pressure in the downstream part of the pneumatic circuit even when the pressure supply is shut down.
Blocking valves are normally assembled directly on cylinders ports in order to maintain the position even in cases of accidental loss of the pilot pressure by preventing a sudden loss of pressure in the cylinder chambers.
Unidirectional and bidirectional version are both available.
The unidirectional version allows free air to flow in one direction while requires a pneumatic signal to allow air flow in the opposite direction.
The bidirectional version requires a pressure signal to allow air flow in both of the two directions.
The blocking valve cannot be used as safety device.