BODY AS-TRANSFER PUMP 4N1120 - Caterpillar

With the engine in operation, oil is drawn from the hydraulic oil tank to the steering pump. The high-pressure oil then flows to steering control valve (1).Note: Machines that are equipped with the secondary steering attachment have several additional components. The components include the secondary steering pump and electric motor, and a secondary steering valve. If the machine includes secondary steering attachment, the pressure oil from the steering pump flows to the secondary steering valve before the steering control valve.When the steering wheel is stationary, the steering control valve is in the NEUTRAL position. The pressure oil from the steering pump enters steering control valve (1) through inlet (12).From the inlet, the pressure flows to back up relief valve (7) and to directional spool (23). High-pressure oil flows through pilot orifice (16) to create pilot oil pressure which exits the steering valve at port (18). The pilot oil is sent to the hand metering unit.
Illustration 6 g03718010
(A) Pilot oil from steering control valve
(B) Signal pressure to the steering pump
(C) To steering control valve via the neutralizer valves
(27) Hand metering unit Because the steering wheel is stationary, there is no flow of steering pilot oil through the metering unit. However, oil flows through orifices and provides a signal circuit for the steering pump and the rest of the oil is returned to the hydraulic oil tank.Signal pressure oil is connected to the flow compensator valve that is attached to the steering pump. If the pressure of the signal oil is low, the steering pump will destroke. If the pressure of the signal oil is high, the steering pump will upstroke.When the steering wheel is held stationary, there is no demand for pressure oil. The low signal pressure causes the steering pump to destroke. A small amount of oil flow will still compensate for system leakage.Any pilot oil that had been acting on an end of selector spool (3) is forced across an orifice. The oil then flows back to the hydraulic oil tank.Because there is no flow of pilot oil, directional spool (23) is kept in the center of the steering control valve by spring (22).