HOUSING 9W1440 - Caterpillar

Steering Control Valve
Steering Control Valve in Neutral Position (1) Steering control valve.(2) Relief/makeup valve.(3) Holes.(4) Port for left turn (CL).(5) Port for return oil to tank.(6) Backpressure valve.(7) Internal tank passage.(8) Port for right turn (CR).(9) Port for return oil from steering metering pump (T).(10) Holes.(11) Holes.(12) Springs.(13) Passage.(14) Amplifier spool.(15) Internal cavity.(16) Orifices (four).(17) Port for left turn pilot oil (L).(18) Spring.(19) Passage.(20) Passage.(21) Port for pump oil to steering metering pump (P).(22) Passage.(23) Port for accumulator inlet (high pressure) oil.(24) Priority spool.(25) Passage.(26) Load sensing relief valve.(27) Port for load sensing oil (LS).(28) Spring.(29) Combiner/check spool.(30) Orifice.(31) Passage.(32) Pin.(33) Spring.(34) Port for right turn pilot oil (R).(35) Passage.(36) Orifices (six).(37) Passage.(38) Orifices (eight).(39) Directional spool.The steering control valve is pilot operated through the five hydraulic lines connecting it to the steering metering pump in the operator's station. These lines direct the pilot oil from the steering metering pump to shift the spools in the steering control valve. The spools control the amount and direction of pressure oil sent to the steering cylinders. The main components of steering control valve (1) are: priority spool (24), amplifier spool (14), combiner/check spool (29), directional spool (39), relief/makeup valves (2) and backpressure valve (6).Oil Flow
Pressure oil from the accumulators flows through port (23) and fills passages (19), (20), (22) and (25). Oil flows by priority spool (24) and is blocked in passage (19) by amplifier spool (14). Pressure oil is communicated to the steering metering pump through port (21). Once all passages fill with pressure oil, priority spool (24) shifts left, but remains slightly open between passages (19) and (22). This allows a small amount of oil flow (thermal bleed) to the steering metering pump.With the vehicle in the neutral (non-steering) position, left and right pilot oil ports are vented to return oil port (9) through the steering metering pump. With no pilot oil acting on it, directional spool (39) is maintained in the center position by springs (12). Any rolling resistance (opposition), acting on the steering cylinders, creates a pressure increase felt in ports (4) or (8). This pressure increase acts upon the relief/makeup valve in that port.
Relief/Makeup Valve (2) in Relief Position
(2) Relief/makeup valve. (3) Holes. (10) Holes. (40) Poppet. (41) Orifice. (42) Dump valve.If the pressure increase exceeds 24 000 kPa (3500 psi), pressure oil flows through holes (3) and forces poppet (40) up (open). This creates a pressure drop across orifice (41). The pressure drop causes dump valve (42) to move up and allows oil flow through holes (10) into tank passage (7).
Relief/Makeup Valve (2) in Makeup Position
(2) Relief/makeup valve. (10) Holes. (11) Holes. (43) Makeup valve. (44) Makeup seat.This action [relief valve dumping pressure oil into tank passage (7)] causes the makeup portion of the other relief/makeup valve to open and replenish (fill) oil to it's port (low pressure side). The relieved (dumped) pressure oil flows across tank passage (7), backpressure valve (6) and enters holes (11) of the relief/makeup valve. A pressure difference