WHEEL A 8D2268 - Caterpillar

Makeup Valve Operation
Illustration 1 g01592479
(1) Crossover relief valve (2) Spring chamber (3) Spring (4) Passage (5) Spool (6) Passage from the drive loop (7) Supply passage of charge oil from the hydraulic oil filter (8) Charge relief valveIf the drive loop requires oil, the oil pressure in spring chamber (2) and the force of spring (3) is less than the charge oil pressure in passage (4). Charge oil pressure forces valve spool (5) upward. Charge oil flows from passage (7) through passage (4). The oil flows past spool (5) through passage (6) into the drive loop.Relief Valve Operation
Illustration 2 g01592493
(1) Crossover relief valve (2) Spring chamber (3) Spring (4) Passage (5) Spool (6) Passage from the drive loop (7) Supply passage of charge oil from the hydraulic oil filter (8) Charge relief valve (9) Spring (10) Port (11) Pilot valve (12) Passage (13) PassageThe pressure setting for the crossover relief valve is set very high. The valve should not open under normal operating conditions. The crossover relief valve should open in order to reduce pressure spikes. Pressure spikes usually occur from external forces.Oil flows from the drive loop to crossover relief valve (1) through passage (6). Hydraulic oil flows through passage (9) into spring chamber (2). Oil pressure combines with the force of spring (3). The oil acts against pilot valve (11) which is held closed by spring (13) .If the oil pressure in spring chamber (2) rises enough to overcome the force of spring (13), the oil pressure causes pilot valve (11) to move upward. When pilot valve (11) moves upward, the spool (5) of the relief valve is also free to move upward. The high pressure oil from drive loop (6) can escape into passage (4) .