VALVE 2990938 - Caterpillar

Low Speed
Illustration 7 g06193795
(2) Travel speed solenoid
Illustration 8 g06244188
Left travel motor - low speed
(A) Indicator for low speed
(B) Indicator for high speed
(C) Machine ECM
(2) Travel speed solenoid
(12) Pump 2
(16) Pump 2 pressure sensor
(20) Left travel control valve
(21) Main control valve
(26) Swivel
(27) Directional control spool
(28) Left travel motor
(34) Travel speed control switch
(37) Left travel lever/pedal
(39) Swashplate control piston
(40) Passage (return oil)
(41) Swashplate
(42) Motor rotary group
(43) Motor brake
(44) Passage (supply oil)
(45) Displacement change valve
(46) Passage
(47) Pilot passage
(48) Pilot supplyWhen travel speed control switch (34) is set at the LOW SPEED position, indicator (A) illuminates. An electrical signal is sent to machine ECM (C). The machine ECM de-energizes travel speed solenoid valve (2). The spool shifts to the right from spring pressure, blocking pilot supply (48) from flowing into the travel motor.Oil flows from pump 2 (12) into main control valve (21). The ECM energizes left travel forward solenoid (19) sending pilot oil to left travel control valve (20) causing the valve to shift. The shifted valve allows pump oil to flow to swivel (26) and into travel motor (28). The oil enters the motor at port (B) and shifts directional control valve (27) to the left. Supply oil flows through the control valve into two different paths. In one path oil flows to passage (44), and into motor rotary group (42) for forward travel. With displacement change valve (45) shifted to the left from spring pressure, the oil in swashplate control piston (39) drains to tank through passage (46). The swashplate shifts to maximum displacement. At maximum displacement, the motor rotary group displaces a larger amount of oil flow. Therefore, rotational speed of the left travel motor decreases.The return oil from the motor rotary group flows through passage (40), directional control valve (27), and swivel (26). The return oil then flows back to main control valve (21) where it flows back to the hydraulic tank.At the same time, oil flows through directional control valve (27), to motor brake (43). The oil pressure pushes the brake piston back against spring pressure releasing the brake. Once the brake is released and enough pressure is available to turn the motor, the track will start to move. In low speed, the left track moves slowly and better traction is achieved.The right travel motor functions in the same manner as the left travel motor with the travel speed control in the LOW SPEED position.High Speed
Illustration 9 g06244391
Left travel motor - high speed
(A) Indicator for low speed
(B) Indicator for high speed
(C) Machine ECM
(2) Travel speed solenoid
(12) Pump 2
(16) Pump 2 pressure sensor
(20) Left travel control valve
(21) Main control valve
(26) Swivel
(27) Directional control spool
(28) Left travel motor
(34) Travel speed control switch
(37) Left travel lever/pedal
(39) Swashplate control piston
(40) Passage (return oil)
(41) Swashplate
(42) Motor rotary group
(43) Motor brake
(44) Passage (supply oil)
(45) Displacement change valve
(46) Passage
(47) Pilot passage
(48) Pilot supplyWhen travel speed control switch (34) is set at the HIGH SPEED position, indicator (B) illuminates. An electrical signal is sent to machine ECM (C). Pressure sensor (16) also sends an electrical signal to