621H, 623H and 627H Wheel Tractor-Scrapers Braking and Hydraulic Fan System Caterpillar

Illustration 1	g02278663
(1) Passage (2) Passage (3) Check ball

The shuttle valve sends pressure in order to signal the pump to meet the pressure demand of the hydraulic fan and service brake accumulators. When the service brake accumulators pressure is below the cut in pressure, the pressure in passage (2) is greater than the pressure in passage (1). The pressure forces check ball (3) to the left and pressurized oil to exit through passage (1). This signals the pump to upstroke. When the service brake accumulators system reaches the cut out pressure, the signal pressure for the brake becomes zero. The check ball (3) moves to the right. This movement of the ball allows the pump to sense the requirement for the fan system.