BP1U120-08J5 AirCom Pneumatic

General_operational_description:

The volume booster and proportional valve are fed by the supply
pressure. When no command signal is applied the outlet pressure
behind the booster is zero. When the command signal is increased
the outlet pressure rises in proportion to it.

Since the transmission ratio is not exactly 1 to 1, a slight
pressure difference occurs between the outlet pressure of the
proportional valve and the booster’s outlet on single loop systems.

This can be balanced by a feedback signal (double loop), though.
At single loop combinations the pressure difference between command
signal and outlet pressure is being ignored because the proportional
valve only refers to its own outlet pressure within the pilot chamber.
The outlet pressure performance is dependent of the volume booster’s
accuracy.