Description; Construction; Mode Of Operation; Technical Data - Danfoss PCVA Instructions Manual

Instructions
3

Description

4

Technical Data

4 | © Danfoss | 2016.06
PCVA, PCVSAA

3.1 Construction

Pilot controller SAVA
Throttling valve
only DN150-250

3.2 Mode of Operation

The control unit consists of the PCV-VFG21 valve
unit, installed in the main pipe, and the pressure
relief controller AVA or safety pressure relief
controller SAVA 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 relief controller, the controller
keeps the pressure before the controller unit
in accordance with the preset setpoint on a
constant level.
As a safety pressure relief controller, the
controller guarantees that the pressure is not
exceeded before the control unit. If the controller
diaphragm is
damaged, the valve is closed via the second
diaphragm.The setpoint for the pressure is
adjusted by pre-stressing the setpoint spring of
the pilot controller.
The valve and the pilot valves are
pressurebalanced. The setpoint for the
pressure is adjusted by prestressing the
setpoint spring of the pilot controller. The
valve unit in the main pipe is opening on
rising pressure. The pilot controllers in the
bypass line are closing on rising pressure.
Technical data, see rating plates and the PCV
data sheet.
Throttling element
Valve Unit PCV-VFG21
Throttling valve
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 shockfree 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.
VI.JA.D2.5B