Charge Pressure Relief Valve (CPRV)
The charge pressure relief valve is a direct acting poppet valve that opens and discharges fluid to the
pump case when pressure exceeds a designated level. The charge pressure relief valve maintains charge
pressure at a designated level above case pressure.
This level is nominally set with the pump running at 1800 min
-1
(rpm), and with a fluid viscosity of 32
mm²/s [150 SUS]. In forward or reverse, charge pressure will be slightly lower than in neutral position. The
model code of the pump specifies the charge pressure relief valve setting. Typical charge pressure
increase from 1.2-1.5 bar per 10 l/min [17.4-21.8 psi per 2.64 US gal/min]. For external charge flow the
CPRV is set according to the table below:
Standard level setting is ∆p = 21 ± 1.1 bar [304 ± 16 psi] with the pump running at 1500 min
-1
(rpm) and
flow = 23.80 - 29.5 l/min [ 6.3 - 7.8 US gal/min]. Typical charge pressure increase is 2 bar per 10 l/min [29
psi per 2.64 US gal/min].
CPRV flow setting for external charge supply
Tandem 045/053 Single 045/053 Single 060—165 Single 210/250
30 l/min [7.9 US gal/min] 15 l/min [3.9 US gal/min] 22.7 l/min [6.0 US gal/min] 40.0 l/min [10.6 US gal/min]
Charge pressure relief valve
Electrical Displacement Control (EDC)
An EDC is a displacement (flow) control. Pump swash plate position is proportional to the input
command and therefore vehicle or load speed (excluding influence of efficiency), is dependent only on
the prime mover speed or motor displacement.
The Electrical Displacement Control (EDC) consists of a pair of proportional solenoids on each side of a
three-position, four-way porting spool. The proportional solenoid applies a force input to the spool,
which ports hydraulic pressure to either side of a double acting servo piston. Differential pressure across
the servo piston rotates the swash plate, changing the pump‘s displacement from full displacement in
one direction to full displacement in the opposite direction.
A serviceable 125 μm screen is located in the supply line immediately before the control porting spool.
Under some circumstances, such as contamination, the control spool could stick and cause the pump to
stay at some displacement.
Service Manual
H1T 045/053, 060/068 Axial Piston Tandem Pumps
Operation
16 |
©
Danfoss | September 2020 AX152886481761en-000405
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