sides of the working loop to the common charge gallery. The bypass function allows you to move a
machine or load without rotating the pump shaft or prime mover.
C
Caution
The HPRV valves are not tow valves. Damage to the pump and motor can occur when operating without
charge flow. Limit vehicle/machine movement to no more than 20% of maximum speed and no longer
that three minutes. Reseat the HPRV valves after vehicle/machine movement.
System Schematic for Single Pump
The schematic below shows the function of an H1P axial piston variable displacement pump with electric
displacement control (EDC).
A
B
MA
S
M3
C2
C1
M4
M5
MB
L4
L2
M6 1
2
R2
R1
M14
F00B F00A
CW
P003 418E
The Basic Closed Circuit
Hydraulic lines connect the main ports of the pump to the main ports of the motor. Fluid flows in either
direction from the pump to the motor and back. Either of the hydraulic lines can be under high pressure.
In pumping mode the position of the pump swashplate determines which line is high pressure as well as
the direction of fluid flow.
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
H1P 069—H1P 250 Axial Piston Single Pumps
Operation
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©
Danfoss | September 2020
AX152886482551en-000504
