Overview
This section describes the operation of pumps and their serviceable features. It is a useful reference for
readers unfamiliar with the function of this specific pump.
General description and cross-sectional view
The Series 42 pumps are servo controlled, axial piston pumps designed for closed circuit applications. The
input shaft turns the pump cylinder block containing nine reciprocating pistons that are held to the
swashplate with a block spring. Each piston has a brass slipper connected to one end by a ball joint. The
reciprocating movement occurs as the slippers slide along the inclined swashplate during rotation. As
each piston cycles in and out of its bore, fluid is drawn from the inlet and displaced to the outlet thereby
imparting hydraulic power to the system. Via the valve plate, one half of the cylinder block is connected
to low pressure and the other to high pressure. Clearances allow a small amount of fluid 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.
The angle of the swashplate controls the volume of fluid displaced into the system. The servo piston
forces the swashplate into an inclined position (into stroke). Internal moments and centering springs
within the servo piston return the swashplate to the neutral position (out of stroke).
Cross section
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