Open Center Pvp; Closed Center Pvp - Danfoss PVG 32 Technical Information

Technical Information
PVG 32 Proportional Valve Group
PVG general description

Open center PVP

Closed center PVP

8 | © Danfoss | November 2017
Description of the example: PVG 32 with open center PVP (fixed displacement pump) and PVB with flow
control spool.
When the pump is started and the main spools in the individual basic modules (11) are in the neutral
position, oil flows from the pump, through connection P, across the pressure adjustment spool (6) to
tank. The oil flow led across the pressure adjustment spool determines the pump pressure (stand-by
pressure).
When one or more of the main spools are actuated, the highest load pressure is fed through the shuttle
valve circuit (10) to the spring chamber behind the pressure adjustment spool (6), and completely or
partially closes the connection to tank to maintain pump pressure. Pump pressure is applied to the right-
hand side of the pressure adjustment spool.
The pressure relief valve (1) will open when the load pressure exceed the set value, diverting pump flow
back to tank.
In a pressure-compensated basic module the compensator (14) maintains a constant pressure drop
across the main spool – both when the load changes and when a module with a higher load pressure is
actuated.
With a non pressure-compensated basic module incorporating a load drop check valve (18) in channel P,
the check valve prevents return oil flow.
The basic module can be supplied without the load drop check valve in channel P for functions with over-
center valves.
The shock valves PVLP (13) with fixed setting and the suction valves PVLA (17) on ports A and B are used
for the protection of the individual working function against overload and/or cavitation.
An adjustable LS pressure limiting valve (12) can be built into the A and B ports of pressure-compensated
basic modules to limit the pressure from the individual working functions. The LS pressure limiting valves
save energy compared with:
•
PVLP all the oil flow to the working function will be led across the combined shock and suction valves
to tank if the pressure exceeds the fixed setting.
•
LS pressure limiting valves an oil flow of about 2 l/min [0.5 US gal/min] will be led across the LS
pressure limiting valve to tank if the pressure exceeds the valve setting.
Please see the sectional drawing
Description of the example: PVG 32 with closed center PVP (variable displacement pump) and PVB with
flow control spool.
In the closed center version of PVP an orifice (5) and a plug (7) have been fitted instead of the plug (4).
This means that the pressure adjustment spool (6) will open to tank when the pressure in channel P
exceeds the set value of the pressure relief valve (1). The pressure relief valve in PVP should be set at a
pressure of approx. 30 bar [435 psi] above maximum system pressure (set on the pump or external
pressure relief valve).
In load sensing systems the load pressure is led to the pump control via the LS connection (8). In the
neutral position the pump load sense control sets the displacement so that leakage in the system is
compensated, to maintain the set stand-by pressure. When a main spool is actuated the pump load sense
control will adjust the displacement so that the set differential pressure (margin) between P and LS is
maintained.
Please see the sectional drawing
Sectional view on page 9 for better understanding of this example.
Sectional view on page 9 for better understanding of this example.
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