Theory of Operation
inclined thrust plate. To reverse rotation, oil flow is
The rotating group consists of a cylinder block (A) with
reversed. A small amount of supply oil flows through
nine pistons and slippers (P). The cylinder block is
the center of each piston to ball joint and to face of
connected to the output shaft (M). Each piston is
slipper for lubrication.
connected to a slipper by a ball joint. Slippers slide on
the inclined thrust plate (O) forcing the cylinder block
The motor is internally lubricated from leakage inside
to turn. Retainer (L) holds the slippers on the thrust
the motor. Lubrication oil is routed up through the
plate and the retainer itself is held against the slippers
cover to the hydraulic oil tank.
by force pins (J) and spring (C).
The swing motor park brake is spring applied and
Oil from swing control valve is routed through cover
hydraulically released. The plates in the brake pack (I)
(D), valve plate (E), and port (B) to the pistons.
are connected to the housing. The disks are connected
to and rotate with the cylinder block. When the pilot
In operation, high pressure supply oil enters the
controllers are in neutral, pilot oil is blocked from the
cylinder bores through ports forcing pistons down
piston (H) by the swing park brake release valve (Q).
against inclined thrust plate. The slippers slide down
The brake springs squeeze the plates and disks
the inclined thrust plate causing the rotating group to
together to prevent the upperstructure from swinging.
turn. The output shaft is turned by the cylinder block.
The swing park brake is released when the swing,
Swing speed varies depending on the amount of
boom, arm, or bucket function is actuated.
supply oil delivered by the pump through the control
During the second half of motor's revolution, low
pressure oil is discharged as pistons slide back up the