Instructions
PCVD, PCVSAD
4 | © Danfoss | 2016.05
VI.JA.C3.5B
Pilot controller AVD
Throttling element
Valve Unit PCV-VFG2
Throttling valve
Throttling valve
only DN150-250
3 Description
3.1 Construction
3.2 Mode of Operation
The control unit consists of the PCV-VFG2 valve
unit, installed in the main pipe, and the pressure
controller AVD or safety shut-off-valve SAVD
installed as pilot controller in the bypass. In the
bypass line, a throttle element is installed in front
of the pilot controllers.
As a pressure reducer, the controller keeps the
pressure behind the controller unit in accordance
with the preset setpoint on a constant level.
As a safety shut-off valve, the controller
guarantees that the pressure is not exceeded. If
the controller diaphragm is damaged, the valve
is closed via the second diaphragm.
The valve and the pilot valves are pressure-
balanced.
The setpoint for the pressure is adjusted by
pre-stressing the setpoint spring of the pilot
controller.
Valve unit PCV-VFG 2
The valve unit in the main pipe is opening on
rising pressure. The pilot controllers in the
bypass line are closing on rising pressure.
In case of small flow rates, the valve in the main
pipe remains closed through the pressure spring
in the actuator of the valve unit. The pressure is
exclusively controlled by the pilot controller.
If the flow rate in the bypass is increased, the
pressure in the throttle element (Venturi nozzle)
decreases.
The reduced pressure acts through an impulse
tube upon the lower chamber of the actuator
of the valve unit. The main valve is thus opened
shock-free and continuously.
If the flow rate is reduced, the pressure in the
throttle element raises and the main valve closes.
This sequential switching guarantees an
operation free of vibrations and a small control
deviation over a wide positioning range.
4
Technical Data
Technical data, see rating plates and the PCV
data sheet.
