Operation; Pvg 32 Group With Open Center Pvp (Pvb With Flow Control Spool); Pvg 32 Group With Closed Center Pvp (Pvb With Flow Control Spool) - Danfoss PVG 32 Service Manual

Service Manual
PVG 32 Proportional Valve Group

Operation

PVG 32 group with open center PVP (PVB with flow control spool)

PVG 32 group with closed center PVP (PVB with flow control spool)

8 | © Danfoss | February 2017
When the pump starts, 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 actuate, 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.
Pump applies pressure to the right-hand side of the pressure adjustment spool (6). The pressure relief
valve (1) opens if the load pressure exceeds 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 have 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 Load Sensing (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 to the shock valves PVLP. With PVLP all the oil flow
to the working function flows across the combined shock and suction valves to tank if the pressure
exceeds the fixed setting. With LS pressure limiting valves, an oil flow of about 2 l/min [0.5 US gal/min]
flows across the LS pressure limiting valve to tank if the pressure exceeds the valve setting.
In the closed center version, an orifice (5) and a plug (7) are fitted instead of the plug (4). This means that
the pressure adjustment spool (6) only opens to tank when the pressure in channel P exceeds the set
value of the pressure relief valve (1).
In LS systems, the load pressure flows to the pump regulator via the LS connection (8).
In the neutral position the pump 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 regulator
adjusts the displacement to maintain the set differential pressure between P and LS.
The pressure relief valve (1) in PVP should be set at a pressure of approximately 30 bar [435 psi] above
maximum system pressure (set on the pump or external pressure relief valve).
11039167 | AX00000031en-US0301