High Pressure and Charge Relief Valves
Servo Piston Assembly.
(1) High pressure relief valves. (2) Charge relief valve.
High Pressure Relief Valve
High pressure relief valves (1) protect the propel pressure
system. The check part of each valve directs make-up charge
oil to the rotating group to be used in the closed-loop system.
The relief part of each valve protects the system during
operation. If system differential pressure exceeds 29 900 kPa
(4337 psi), high-pressure oil flows through the relief valve to
the low-pressure side of the pump. Each propel pump has two
relief valves, one for FORWARD drive and one for REVERSE
drive. High pressure oil from the pump acts on both the inlet
ends of the high pressure valve spools and the opposite end of
the check valve. As loop pressure becomes larger than charge
oil pressure, the check valve shifts and seats to stop the flow
between the loop and the charge circuit.
Charge Relief Valve
The propel pumps have a charge relief valve. Charge oil
enters the pump through the charge circuit oil line. Charge
relief vale (2) is located in the pump housing. When the
charge relief valve opens, excess oil goes to the hydraulic oil
tank. The charge relief valve is NON -ADJUSTABLE. Charge
pressure is maintained by relief vale in the flushing valve. The
poppet and charge relief valve in the flushing valve determine
the system pressure. The orifice in poppet maintains 1.5 gpm
of flushing/cooling flow out of pumps. If for some reason
pressure exceeds 2825 kPa (410 psi), then relief valve opens,
otherwise it is closed and charge pressure is maintained at
1725 kPa (250 psi) at the flushing valve.