angle of the swashplate and the pistons in the barrel of
the pump get longer strokes.
The oil, at pump output pressure, is also through
When the load on the component in the hydraulic system
passage (18) into pressure reduction valve (15). When
being used gets to 1500 psi (103.5 kg/cm2), the
the oil in chamber (7) can go to the case, there is no
pressure in line (21) is also at 1500 psi (103.5 kg/cm2)
force on piston assembly (5) and the pressure of the oil
and the pressure of the oil moves shuttle valve (20).
through passage (18) moves piston (16). The piston
When the shuttle valve is moved, the oil from pressure
moves swashplate (14).
reduction valve (15) goes through passage ( 19), around
the end of shuttle valve (20) and into the chamber for
Swashplate (14) moves piston assembly (5). Piston
piston (I 2). The force of the oil in piston (12) adds to the
assembly (5) pushes the oil from chamber (7) through
force spring (13) has on valve spool (2). With the
the hole and passage (10) in valve spool (2). The
increase of force on valve spool (2), the output pressure
swashplate stops moving piston assembly (5) when the
of the oil from the pump can go to 3500 psi (246.1
piston assembly moves sleeve (8) to a position where
kg/cm2). The actions of the servo valve and the
the pump output pressure oil in passage (9) can go
pressure reducing valve are the same as when the
around valve spool (2), through the passages in sleeve
output pressure of the oil from the pump was below 2150
(8) and cartridge (6), into chamber (7). When the oil at
psi (151.1 kg/cm2). When the pressure of the oil in line
pump output pressure is in chamber (7) on piston
(21) is less than 1500 psi (103.5 kg/cm2), or there is no
assembly (5), and is in pressure reduction valve (15) on
oil pressure in line (21) when the components in the
piston (16), the swashplate cannot move. The angle of
hydraulic system are not being used, the output pressure
swashplate (14) is now less than when the pistons, in the
of the oil from the pump is at approximately 2150 psi
barrel of the pump, were at the longest stroke.
When there is a decrease in the output pressure from
Add to the washers on spring (13) if the output pressure
the pump, because the load on the component in the
of the oil from the pump is below 2150 psi ( 151.1
hydraulic system which is being used is less, the
kg/cm2 ). Add to the shims on the spring in shuttle valve
pressure of the oil in passage (9) and in passage (II) is
(20) if the shuttle valve moves when the pressure of the
less. The force of the pressure oil from passage (11), on
oil in the hydraulic system to a component is below 1500
valve spool (2), is now less than the force of spring (13).
psi (103.5 kg/cm2 ).
Spring (13) now moves valve spool (2), piston assembly
(5), and swashplate (14). There is now an- increase in
(Pistons now have less than full stroke)
1. Passage for oil from the case. 2. Valve spool. 3. Groove (three) in valve spool. 4. Passage to case. 5. Piston
assembly. 6. Cartridge for servo valve. 7. Chamber. 8. Sleeve. 9. Passage for oil at pump output pressure. 10. Hole
and passage to the case. 11. Passage for oil from pressure reduction valve.