LAMP 1189024 - Caterpillar

Illustration 1 g06252356
Partial schematic
(1) Boom cylinders
(2) Boom lowering control valves
(3) Main control valve
(4) Pilot control valveBOOM RAISE Operation
Illustration 2 g03386150
Boom lowering control valve
(1) Spool
(2) Orifice
(3) Passage
(4) Port
(5) Port (pilot)
(6) Port (boom cylinder head end)
(7) Passage
(8) Check valve
(9) Spring
(10) Port
(11) Line relief valve
(12) Tank port
(13) Drain portDuring a BOOM RAISE, oil from main control valve (3) flows through port (4) in boom lowering control valve (2). As the oil pressure increases, check valve (8) shifts against the force of spring (9). This allows oil to flow through port (10), passage (7), and port (6) to the head end of boom cylinders (1). The rod is extended and the boom raises.BOOM LOWER Operation
Illustration 3 g03386158
Boom lowering control valve
(1) Spool
(2) Orifice
(3) Passage
(4) Port
(5) Port (pilot)
(6) Port (boom cylinder head end)
(7) Passage
(8) Check valve
(9) Spring
(10) Port
(11) Line relief valve
(12) Tank port
(13) Drain portDuring a BOOM LOWER, pilot oil flows from pilot control valve (4) to port (5) of boom lowering control valve (2). The pilot pressure moves spool (1) to the left. Orifice (2) opens allowing oil to flow to passage (3).As the joystick is moved further to the BOOM LOWER position, the pilot pressure in port (5) increases. Spool (1) shifts further to the left which allows more oil from passage (7) to flow to passage (3). Oil from the head end of boom cylinder (1) now flows through port (6), to port (4), and then to main control valve (3). The rod of boom cylinder (1) retracts and the boom lowers.Manual Boom Lower
Illustration 4 g02224018
(14) Port
(15) Seat
(16) Locknut
(17) Valve
(18) Ball
(19) PortAs seat (15) is turned counterclockwise, ball (18) will shift. As ball (18) is shifted, oil is allowed to flow through port (14) and valve (17) to port (19). Oil from the head end of boom cylinder (1) flows through port (19) to the hydraulic tank. Once oil flow is allowed to flow to the hydraulic tank, the boom will lower.Reference: For information on the location of the manual lower valve, see Operation and Maintenance Manual, "Equipment Lowering with Engine Stopped".