FITTING 1136928 - Caterpillar

Illustration 1 g06164875
Steering System Hydraulic Schematic
(1) Steering priority valve
(2) Pressure tap
(3) To charge filter inlet
(4) Anticavitation check valve
(5) Metering unit
(6) Steering cylinder
(7) Makeup valve
(8) Line relief valve
(9) Line relief valve
(10) Main relief valve
(11) Steering pump
(12) From suction strainer
(13) Steering control spool
(14) Metering pump
(15) Makeup valveIllustration 1 shows the steering hydraulic system operating during straight travel.Steering pump (11) supplies oil to steering priority valve (1). The steering priority valve acts as an on-demand flow priority valve. The valve maintains pressure at, or equal to, the value of the spring combined with load sensing pressure. As pump supply pressure is equalized, oil is directed out port "PF" of the pump. This oil is sent to port "P" of metering unit (5). Steering pump supply pressure is measured at pressure tap (2).When the steering wheel is in the center position, the center envelope of steering control spool (13) is active. Supply oil from steering pump (11) enters metering unit (5) through port "P". This oil is blocked at the control spool. At the same time, pump supply pressure acts against both sides of steering priority valve (1). In this case, the valve continuously shifts as system demands downstream are met.The steering priority valve (1) directs flow out of port "PF". The flow from port "PF" is on-demand priority flow designated for steering. When pump supply pressure at port "PF" is sufficient, the pressure drop across the orifice causes the priority valve to shift. As the valve shifts, port "PF" and port "EF" are open simultaneously. In this case, steering supply flow is available at port "PF" always. Charge supply oil flow exits at port "EF" and is directed to charge filter inlet (3).In the straight travel condition, the charge oil backfills metering unit (5) through port "T". Reduced charge pressure from the center envelope of control spool (13) is directed out port "LS" of metering unit to port "LS" of steering pump (11). This oil flow maintains the metering unit at system temperature.Line relief valves (8) and (9) limit the maximum pressure in steering cylinder (6). These relief valves act as shock valves for the steering system. The valves are set at the factory to open when the pressure in the steering cylinder reaches 27600 kPa (4003 psi). The line relief valves are not adjustable.If the steering system does experience a shock load, the makeup valve (7) or (15) in the low-pressure side of steering cylinder (6) opens. This action allows oil to enter the low-pressure side of the cylinder, preventing cylinder cavitation.
Illustration 2 g06164883
Steering System Hydraulic Schematic
(1) Steering priority valve
(2) Pressure tap
(3) To charge filter inlet
(4) Anticavitation check valve
(5) Metering unit
(6) Steering cylinder
(7) Makeup valve
(8) Line relief valve
(9) Line relief valve
(10) Main relief valve
(11) Steering pump
(12) From suction strainer
(13) Steering control spool
(14) Metering pump
(15) Makeup valveIllustration 2 shows the steering hydraulic system operating in a left turn (bottom envelope active).Pump supply oil enters metering unit (5) through port "P". When the steering wheel is rotated to the left, steering control spool (13)