Pressure Override Valve

TM 5-3895-383-24 Pressure Override Valve SMCS Code: 5117 Illustration 25 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 Illustration 26 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. 10-33