Introduction; Basic Hydraulic Circuits - Sauer Danfoss 51 Series Service Manual

Bent Axis Variable Displacement Motors

Introduction

The purpose of this manual is to provide information
necessary for the normal servicing of the Series 51
family of variable displacement hydrostatic motors.
This manual includes unit and component descrip-
tion, troubleshooting, adjustments, and minor repair
procedures. By following the procedures in this
manual, inspections and minor repairs may be per-
formed without affecting the unit warranty.
A Series 51 motor does occasionally require servic-
ing, and these units are designed to meet this require-
ment.
Many repairs or adjustments can be completed with-
out removing the unit from the vehicle or machine,
provided the unit is accessible and can be thoroughly
cleaned before beginning any procedures.

Basic Hydraulic Circuits

INPUT
PV
FLOW (BI-DIRECTIONAL)
RESERVOIR
Fig. 0-1 - Basic Closed Circuit
FLOW
(UNI-DIRECTIONAL)
INPUT PUMP
Fig. 0-2 - Basic Open Circuit
4
CASE
DRAIN
LINE
OUTPUT
MV
FLOW
(BI-DIRECTIONAL)
OUTPUT
MV
CASE
DRAIN
RESERVOIR
LINE
Dirt or contamination is the greatest enemy of any
type of hydraulic equipment. The greatest possible
cleanliness is necessary when starting up the sys-
tem, changing filters, or performing any other service
procedure.
For Technical Information on Series 51 motors, refer
to publication BLN-10042 or 368753.
For Fluid Quality Requirements, refer to publication
BLN-9987 or 697581.
Sauer-Sundstrand provides a complete repair serv-
ice for its products. Contact any Sauer-Sundstrand
Authorized Service Center for details. Sauer-Sund-
strand Authorized Service Center locations are listed
in publication BLN-2-40527 or 698266.
Closed Circuit
The main ports of the pump are connected by hydrau-
lic lines to the main ports of the motor. Fluid flows in
either direction from the pump to the motor then back
to the pump in this closed circuit. Either of the hydrau-
lic lines can be under high pressure. The direction
and speed of fluid flow (and the motor output shaft
rotation) depends on the position of the pump swash-
plate. The system pressure is determined by the
machine load.
Open Circuit
The outlet port of the pump is connected by a hydrau-
lic line to a directional control valve. The working ports
51000001
of this valve are connected to the main ports of the
motor. When the valve is actuated, fluid flows first
from the pump to the valve. The valve then directs the
fluid to the motor in either direction. The direction of
fluid flow (and motor output shaft rotation) depends
on the direction the control valve is shifted. The speed
of fluid flow (and motor output shaft speed) depends
on pump output volume and the distance the control
valve is shifted. The system pressure is determined
by the machine load.
Fluid returning from the motor is routed through the
control valve to the reservoir. Additional components
may be necessary to provide dynamic braking and to
deal with over-running loads.
51000002
Series 51
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