Pressure Override Valve
SMCS Code: 5117
Pressure Override Relief Valve
(1) Adjustment screw. (2) Locknut. (3) Spring. (4) Passage.
(5) Valve. (6) Passage. (7) Piston. (8) Chamber. (9)
Passage. (10) Slug. (11) Passage.
The pressure override relief (POR) valve is located on the
propel pump. The POR valve limits he maximum pressure on
both sides of the propel loop. This valve prevents continuous
dumping of excessive flow through the main relief valves in the
pump. The POR valve is set at 45000 kPa (6525 psi). When
the valve opens, charge oil drains from the pressure side of the
servo valve in the propel pump. As this charge pressure is
drained, the centering springs in the servo valve move the
swashplate toward the minimum pump output at the relief
pressure of the POR valve.
Oil from the high pressure side of the closed loop enters the
POR valve at passage (9) or (11). This is depending on the
side of the closed loop that has the higher pressure. Slug (10)
moves up if the high pressure is in passage (11). The slug
moves down if the high pressure is in passage (9). This sends
the high pressure oil to chamber (8).
When the pressure setting of the POR valve is reached, the
pressure moves piston (7) and valve (5) against spring (3).
This opens passage (4), and the charge oil goes through
passage (6) to the tank. When the charge oil goes to the tank,
the centering springs shift the servo valve and the angle of the
swashplate is reduced.
Valve (5) serves two purposes. The valve modulates in order
to maintain the system pressure at the setting of the POR
valve until the load is reduced. The valve maintains the charge
pressure so that the angle of the swashplate is large enough in
order to compensate for system leakage. The pressure setting
of the POR valve can be adjusted by loosening lockout (2) and
adjusting screw (1).
Charge Relief Valve
SMCS Code: 3213; 5117
Charge Relief Valve
Each propel pump has a charge relief valve. The charge relief
valves are located in the pump housings. When the charge
relief valve opens, excess oil is directed back to the hydraulic
oil tank. The pressure settings for the charge relief valves are
2900 ± 140 kPa (420 ± 20 psi) in the axle propel pump and
3590 kPa (520 psi) in the drum propel pump.