DRIVE GP-FINAL 1920722 - Caterpillar

The flow of pilot oil to either end of spool (13) stops when either STICcontrol lever movement stops, or one of the neutralizer valves is activated. When no pilot oil is acting on either end of spool (13), centering spring (20) returns spool (13) to the HOLD position. As spool (13) returns to HOLD, part of the pilot oil that had been acting on spool (13) is forced across orifice (14) through passage (15) or across orifice (19), back to the hydraulic tank through drain (18).Note: If the machine is turning and moving, the machine will continue moving in the radius of the turn. Releasing the STIC control lever will not return the machine to the straight ahead travel position.
Illustration 2 g06005169
Steering control valve schematic
(2) Inlet
(3) Shuttle valve
(4) Port to tank
(5) Flow control valve
(6) passage
(7) Steering system relief valve
(8) Passage
(11) Orifice
(12) Passage from the left steering neutralizer valve
(13) Spool
(14) Orifice
(15) Passage
(16) Port for left turn
(17) Port for right turn
(18) Drain
(19) Orifice
(20) Spring
(21) passage from the right steering neutralizer valveFor example, a left turn is made, pilot oil flows through passage (12) into chamber (10). This increased pilot pressure on the left side of spool (13) causes spool (13) to move to the right.When the STIC control lever is released, Pilot oil flow to the left side of spool (13) stops. Oil in chamber (10) must be removed before spool (13) can return to the HOLD position. Spring force from spring (20) causes spool (13) to move to the left, when pilot oil pressure is removed from left side of spool (13). As the spool moves, oil in chamber (10) flows through metering orifice (14) through passage (15) and orifice (19) to the spring end of spool (13).When the steering control valve is in the HOLD position, high-pressure oil from the steering pump is stopped by spool (13) causing oil pressure in inlet (2) to increase.The increased oil pressure is felt at flow control valve (5). The oil pressure overcomes the force of the flow control valve spring and causes flow control valve (5) to move to the right. Oil now can flow through the openings in flow control valve (5) and port (4) and return to the hydraulic tank.In the HOLD position, spool (13) blocks the flow of steering oil to the cylinders. The machine is held in the turn position where the STIC control lever was last placed.If an outside force tries to turn the machine whilst the valve spool (13) is in the HOLD position, the pressure will be felt through passages (6) and (8), and also against steering system relief valve (7). Steering system relief valve (7) will open and not allow pressure to rise above the steering system relief valve setting.RIGHT TURN Position
Illustration 3 g01016171
Steering control valve in RIGHT TURN position
(1) Alternate pilot oil port
(2) Inlet
(3) Shuttle valve
(4) Port to tank
(5) Flow control valve
(6) Passage
(7) Steering system relief valve
(8) Passage
(9) Return passage
(10) Chamber
(11) Orifice
(12) Passage from the left steering neutralizer valve
(13) Spool
(14) Orifice
(15) Passage
(16) Port for