Tandem Pumps Design
Danfoss H1 tandem closed circuit piston pumps convert input torque to hydraulic power. The tandem
design powers two independent drive trains for dual-path propel applications.
The two-piece input shaft transmits rotational force to the cylinder block. A splined coupling connects
the front and rear shafts. Bearings at the front, rear, and center of the pump support the shaft. Splines
connect each shaft to a cylinder block. A lip-seal at the front end of the pump prevents leakage where the
shaft exits the pump housing. The spinning cylinder block contains nine reciprocating pistons. Each
piston has a brass slipper connected at one end by a ball joint. The block spring, ball guide, and slipper
retainer hold the slippers to the swashplate. The reciprocating movement of the pistons occurs as the
slippers slide against the inclined swashplates during rotation.
Via the valve plates, one half of each cylinder block is connected to port A or C and the other half to port
B or D. Front and rear sections have independent porting in the center section. As each piston cycles in
and out of its bore, fluid is drawn from one port and displaced to the other thereby imparting hydraulic
power into the system. A small amount of fluid is allowed to flow from the cylinder block/valve plate and
slipper/swashplate interfaces for lubrication and cooling. Case drain ports return this fluid to the
reservoir. An external charge pump (not shown) provides clean, cool fluid to makeup this lubricating flow
and to maintain minimum loop pressure.
The angle of each swashplate controls the volume and direction of fluid displaced into the system. The
servo pistons control the angle of the swashplates. Each pump control, by varying the pressure at the
servo pistons, controls each piston’s position. An electric signal to the control coils transmits the
command from the operator to the pump. Mechanical feedback of the swashplate position to the control
through the feedback pins allows for very precise displacement control and increases overall system
stability. Non-feedback control options do not use the mechanical feedback link.
Cross section view
P106 146E
Slipper
Piston
Cylinder block
Swashplat e
Rear shaft
Electric displacement control
Servo piston
Valve plates
Shaft coupling
Swashplate feedback pin
Front sha ft
Electric displacement control
Servo piston
Swashplate feedback pin
Piston
Slipper
Shaft seal
Swashplat e
Cylinder block
Swashplate bearing
Swashplate bearing
Front shaft bearing
Center shaft bearings
Rear shaft bearing
Service Manual
H1T 045/053, 060/068 Axial Piston Tandem Pumps
Introduction
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Danfoss | September 2020 AX152886481761en-000405 | 9
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