moves and the spring, which controls the angle of the
swashplate, gets more force. When the sprint has more
force, the length of the stroke for the pistons gets an
The shortest stroke of the pistons is when the angle
increase and the pump operates at the high setting. The
of the swashplate is near 0
pump goes to the low setting when the pressure of the oil
to the component gets a decrease.
The pump is driven by the engine crankshaft and
turns at the same speed as the engine. Barrel assembly
(6) and the nine pistons (3) turn when drive shaft (8)
turns. When pistons (3) are at the bottom of their
strokes, the oil from the tank goes through a long inlet
opening in port plate (1), and into barrel assembly (6).
VALVES IN VARIABLE DISPLACEMENT PUMP
1. Head assembly. 5. Pump body. 7. Swashplate. B.
Drive shaft. 9. Servo valve. 10. Bolt. 11. Shuttle
valve. 12.0il line from control valve for the implements.
13. Pressure reduction valve. 14. Bolt.
The increase in the angle of swashplate (7) is stopped by
the end of bolt (10). Shims, under the head of bolt (10),
can be removed for a decrease or added for an increase
As the shaft, barrel assembly and pistons turn thrust
in the angle of the swashplate. Shims, under the head of
plate (4) moves the pistons to the top of their strokes.
bolt (14), are used to keep the angle of the swashplate
The pistons push the oil through the outlet holes in the
from going to 0. If the swashplate stopped at 00, there
port plate and into the hydraulic system. The ball
would be no stroke for pistons (3). If the pistons did not
sockets on the ends of pistons (3) slide on thrust plate
have some stroke, there would be no oil for lubrication or
(4). The thrust plate is on swashplate (7).
to cool the pump. Turn the head of bolt (14) to get less
angle to the swashplate. The bolt is kept in position with
TYPICAL BARREL AND PISTONS
3. Piston (nine). 4. Thrust plate. 6. Barrel assembly.
The angle of swashplate (7) changes the displace ment
of pistons (3) (changes the stroke of the pistons). The
3. Piston (nine). 6. Barrel assembly. 7. Swashplate.
longest stroke of the pistons is whet the angle of the
The actions of servo valve (9) and pressure reduction
swashplate is approximately 16
valve (13) control the stroke of pistons (3) by moving
swashplate (7) when either more or less pump oil is
needed by the components in the hydraulic system.