D3K2, D4K2 and D5K2 Track-Type Tractor Systems Caterpillar

The crossover relief valve performs two functions within the piston pump. The crossover relief valve operates as a makeup valve in order to provide makeup oil to the drive loop for any oil leakage. The crossover relief valve also operates as a makeup valve in order to provide makeup oil for oil flow through the flushing valve. Also, the crossover relief valve protects the systems from high-pressure spikes.

Makeup Valve Operation

Illustration 1	g00854676
(1) Valve cartridge (2) Spring (3) Passage from the low-pressure side of the drive loop (4) Passage (5) Supply passage of charge oil from the hydraulic oil filter

When the pressure in passage (3) and the force of spring (2) is less than the charge oil pressure in passage (4), charge oil pressure forces valve cartridge (1) upward. Charge oil flows from passage (5) through passage (4) to valve cartridge (1). The oil flows past valve cartridge (1) through passage (3) back to the drive loop.

Relief Valve Operation

Illustration 2	g02952018
(2) Passage from the high-pressure side of the drive loop (3) Poppet (4) Spring (5) Spring retainer

Oil flows from the drive loop to the crossover relief valve through passage (2). Pressure oil acts against the surface of poppet (3). Since poppet (3) screws into spring retainer (5), the spring retainer attempts to compress spring (4). When the pressure of the oil overcomes the force of spring (4), the poppet moves upward. Oil flows from passage (2) past poppet (3) to the low-pressure side of the loop.