Charge pump
Charge flow is required on all H1 pumps applied in closed circuit installations. The charge pump provides
flow to make up internal leakage, maintain a positive pressure in the main circuit, provide flow for
cooling and filtration, replace any leakage losses from external valving or auxiliary systems, and to
provide flow and pressure for the control system.
Many factors influence the charge flow requirements and the resulting charge pump size selection. These
factors include system pressure, pump speed, pump swashplate angle, type of fluid, temperature, size of
heat exchanger, length and size of hydraulic lines, control response characteristics, auxiliary flow
requirements, hydrostatic motor type, etc. When initially sizing and selecting hydrostatic units for an
application, it is frequently not possible to have all the information necessary to accurately evaluate all
aspects of charge pump size selection.
Unusual application conditions may require a more detailed review of charge pump sizing. Charge
pressure must be maintained at a specified level under all operating conditions to prevent damage to the
transmission. Danfoss recommends testing under actual operating conditions to verify this.
Charge pump sizing/selection
In most applications a general guideline is that the charge pump displacement should be at least 10 % of
the total displacement of all components in the system. Unusual application conditions may require a
more detailed review of charge flow requirements. Please refer to Selection of Drive Line Components,
BLN-9885 for a detailed procedure.
System features and conditions which may invalidate the 10 % guideline include (but are not limited to):
•
Continuous operation at low input speeds (< 1500 min
-1
(rpm))
•
High shock loading and/or long loop lines
•
High flushing flow requirements
•
Multiple Low Speed High Torque motors
•
High input shaft speeds
Basic Information
H1 Axial Piston Pumps, Single and Tandem
System design parameters
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Danfoss | April 2017 11062168 | BC00000057en-US0602 | 31
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