The above drawing is used as a reference for this following description.
The medium entering the valve (inlet port A) passes through the variable presetting opening  which is connected to the ring with the dial  for presetting the desired maximum volumetric flow. Then, the medium flows through the On/Off control valve .
The actuator opens and closes the On/Off control valve . After the presetting, the medium passes through a built-in mechanical differential pressure controller . This differential pressure controller is the heart of the PICV and ensures that the selected volumetric flow is maintained across the whole working range and independent of the inlet pressure P1.
The PICV VQ..46..Q are additionally equipped with 2 pressure test points (P+, P-). These pressure test points allow the measurement of the differential pressure across the PICV in order to check if Δp is sufficient to reach Δpmin. For that purpose, the electronic manometer ALE10 can be used.
Inlet medium (inlet port)
Outlet medium (outlet port)
Ring with dial for presetting
Differential pressure controller maintains the pressure P1 – P2 constant across the presetting 
On/Off control valve with mounted actuator
Pressure at inlet of PICV
Pressure at outlet of presetting
Pressure at outlet of PICV
P/T port, pressure test point with red ribbon 
P/T port, pressure test point with blue ribbon 
The manual control knob can be fitted to protect the valve stem and facilitates manual control of the PICV during commissioning. The manual control knob is delivered loose in the box.
The valve is open. To close the valve, turn the manual knob clockwise.
The valve must be open to purge the system.