SEAT-VALVE 8D4595 - Caterpillar

Illustration 2 g00561237
Main Control Valve Compartment (Typical Example) (2) Manual valve lock of parking brake valve (3) Manual valve operation of transmission shiftThe transmission shift/parking brake control valve is a solenoid operated valve. The parking brake solenoid activates the drive line parking brake in the transmission. The transmission shift solenoid controls the shifting of the transmission gears. Both valves are energized by toggle switches on the instrument panel.The valve block includes the parking brake control valve and the transmission shift control valve. Both solenoid valves are two-way valves with spools and springs. The parking brake spool and the transmission shift spool are closed off at the top by the solenoid valves, and at the bottom by the sealing plugs. The left section of the valve block is made up of the parking brake and the right section is made up of the transmission shift.The relief valve and a hydraulic accumulator are also used for controlling the parking brake. The relief valve that is installed in the valve block consists of a ball and a spring. The relief valve pressure setting is 1200 to 1400 kPa (175 to 200 psi).Low transmission clutch pressure switch is installed at port "DS". When the transmission clutch pressure is less than 2500 kPa (360 psi), the low transmission clutch pressure switch is closed. The switch makes contact in order to light the low clutch pressure indicator. This also deactivates the travel activation solenoid.Applied Parking Brake
Illustration 3 g00561314
Transmission Shift/Parking Brake Control Valve (1) Parking brake solenoid (2) Manual valve lock of parking brake valve (3) Manual valve operation of transmission shift (4) Transmission shift solenoid (5) Spool (6) Port "P" (7) Passage (8) Passage (9) Passage (10) Port "T" (11) Port "A" (12) Passage (13) Port "DS" (14) Port "S" (15) Passage (16) Spring (17) Sealing plug (18) Relief valve (19) Passage (20) Passage (21) Spring (22) Sealing plug (23) Spool (24) Valve block (25) Passage (26) Ball (27) Nut (28) Adjustment screw (29) Cap (30) SpringWhen the parking brake switch on the right console is in the ON position or the left console is in the RAISED position, the parking brake solenoid is de-energized. When the parking brake solenoid is de-energized, the clutch pressure at ports "A" and "B" is returned to the tank. The clutch spring forces the clutch piston against the clutch discs. Now, the clutch discs cannot rotate and the parking brake is applied. When the parking brake is activated, the travel activation solenoid is de-energized in order to block the pilot pressure to the travel pilot control valve. This prevents any activation of the travel circuit while the parking brake is applied.When the parking brake switch is in the ON, the parking brake de-energizes the solenoid of the parking brake control valve. This allows control spool (5) to move upward and control spool (5) will stop the flow of oil between passages (7) and (8). Since passages (8) and (9) are connected, the pressure oil in passage (20) goes to