ORIFICE 2615659 - Caterpillar

Illustration 1 g00861098
(1) Front service brakes (2) Parking brake (3) Brake control valve (Parking) (4) Limit switch (Parking brake) (5) Rear service brakes (6) Pressure switch (Parking brake oil) (7) Combination Valve (8) Limit switch (Stop light) (9) Left pedal position sensor (10) Foot brake control (11) Brake accumulator (12) Brake control valve (Service) (13) Breaker relief valve (14) Hydraulic tank and filter (Implement and braking) (15) Gear pump (Pilot and braking) (16) Relief valve (Braking system) (A) Pressure test point (B) Implement system pilot control valve (C) Pressure test point (D) Fluid sampling port (E) Pressure test point for the accumulatorThe 844 Wheel Tractor and the 990 Series II Wheel Loader have two separate hydraulic systems. One system supplies pressure to the hydraulic fan and the steering systems. The other system supplies pressure to the braking and implement systems. The braking and implement systems share the same hydraulic oil tank. Pressure for the brake system and the implement system is supplied from two different pumps.Oil is supplied to the brake system by gear pump (15). The pump also supplies pressure to the implement pilot system. If the oil pressure is 22750 400 kPa (3300 60 psi), system relief valve (16) will divert the flow of oil to the hydraulic tank. The oil is diverted into a front brake circuit and a rear brake circuit by combination valve (7). The oil is also supplied to service brake control valve (12) and parking brake control valve (3) .Nitrogen charged accumulators (11) in the service brake circuits will fill with the oil until the pressure of 13000 1000 kPa (1875 145 psi) is reached. Pressure oil will then be diverted from the accumulators to the implement pilot system.Check valves in combination valve (7) prevent the oil from flowing back through the valve. A flow control valve in the combination valve will control the maximum oil pressure to the accumulators if the charging valve spool does not work correctly. Service brake control valve (12) is in the circuit between the accumulator and the service brakes. When either brake pedal is pushed, oil from the accumulator flows to the service brake at each wheel through service brake control valve (12). The heat from the friction of the brakes is removed by the oil in the final drive housing. After the brakes have been applied several times, there is a smaller volume of oil in the accumulator which allows the pressure to drop. When the pressure drops to 11500 600 kPa (1675 85 psi), combination valve (7) diverts oil from pump (15) to accumulators (11) until the pressure again rises to cutoff pressure.The application of pressure to either foot brake pedal (10) will apply pressure to the service brakes. The application of any pressure to the right foot brake pedal will also disengage the throttle lock. The application of light pressure to the left foot brake pedal will limit the drive train torque by limiting the impeller clutch