DIFFERENTIAL GP 3921740 - Caterpillar

Illustration 1 g01129689
Hydraulic Schematic for the Secondary Steering System
(1) Left steering cylinder
(2) Right steering cylinder
(3) Steering control valve
(4) Check valve
(5) Diverter valve
(6) Secondary steering relief valve
(7) Check valve
(8) Spool valve
(9) Steering quad check valves
(10) Steering pressure reducing valve
(11) Selector and pressure control valve
(12) Steering neutralizer valves
(13) Secondary steering pump
(14) Secondary steering check valve
(15) Steering pilot valve for machines that are equipped with STIC steering
(16) Steering pilot check valve
(17) Steering pump
(18) Hydraulic tank
(A) Low oil pressure switch Note: Secondary steering is an optional attachment that is available on the 834H Wheel Dozer.The secondary steering system supplies the steering oil only if the following conditions exist. The primary steering pump fails, or the engine stops while the machine is still moving.The main components of the secondary steering system follow: hydraulic tank (18), secondary steering pump (13), secondary steering relief valve (6) and diverter valve (5).Note: Diverter valve (5) and secondary steering relief valve (6) are part of steering control valve (3).During normal machine operation, steering pump (17) draws oil from hydraulic tank (18). The pump then sends the oil through check valve (7). Check valve (7) is located in steering control valve (3). The oil then flows to pressure reducing valve (10), and steering cylinders (1) and (2).
Illustration 2 g01129728
Location of the Secondary Steering Pump
(13) Secondary steering pump.
As the machine starts to move, oil begins to flow from secondary steering pump (13). Secondary steering pump (13) is a ground driven pump that is attached to the output transfer gears of the transmission. If the machine is moving forward or backward, the pump will provide oil flow.With secondary steering pump (13) in operation, oil flows into diverter valve (5). If steering pump (18) maintains a steady pressure, that pressure remains greater than the pressure from secondary steering pump (11). This keeps check valve (4) against the seat for the check valve. This also keeps the spool in diverter valve (5) in the DOWNWARD position.With the spool in diverter valve (5) in the DOWNWARD position, the oil from secondary steering pump (13) flows back to hydraulic tank (18).When steering pump (17) does not maintain adequate system pressure, and if the machine is in motion, a spring on the bottom of the diverter valve spool forces the spool upward. The oil from secondary steering pump (13) now flows through diverter valve (5). The oil then flows through check valve (4) on the flow path to check valve (7).Because primary steering pump (17) has stopped working, or because the engine has stopped, the secondary steering oil forces check valve (7) to seat. When check valve (7) is seated, oil from secondary steering pump (13) cannot flow to steering pump (17).When check valve (7) is seated, the pressure oil from secondary steering pump (13) flows to pressure reducing valve (10), and to steering cylinder (1) and steering cylinder (2).Pressure reducing valve (10) reduces the pressure of the secondary steering oil to pilot pressure. The pilot oil then flows through secondary steering check valve (14), and steering pilot