Carriage Tilt System

TM 10-3930-673-34

with the greatest load to be sensed by the pump. As the load of the attachment control valve changes, the

position of the swash plate angle changes in the piston pump.

When the electric joystick is in the center position, all solenoids of the attachment control valve are de-

energized and centering springs keep the control valve spools in the center (hold) position.

By moving the electric joystick forward, the top left solenoid is energized. The solenoid allows pilot oil to flow

through the solenoid and push the spool in the top section towards the right of the machine. The main flow of

hydraulic oil goes through the top section, pilots open a load check poppet and allows oil to flow from the work

port to the attachment cylinder. Oil enters the left (rod end) port of the cylinder. The oil pilots open the

counterbalance valve on the head end of the cylinder, allowing oil to flow from the head end of the cylinder.

The cylinder retracts, lowering the attachment. Oil from the cylinder enters the work port of the top section of

attachment control valve and is directed to the return circuit where it is sent to the hydraulic reservoir

through the hydraulic filter.

The load compensating check valve moves up and down as the load and pump pressure change. If the load

increases, the pressure in the work port increases and pushes on the spring side of the load compensating

check valve to block oil passage to the work port. At this short instance, the load compensating check valve is

operating as a load hold check valve. Increased work port pressure is also sent to the piston pump through the

sensing line.The pump output pressure increases sufficiently to maintain the 400 psi (2758 kPa) pressure

differential. The increase in pump pressure is now sensed at the smaller end of the load compensating check

valve and the valve moves up allowing oil flow to the work port again.

If the electric joystick is moved rearward, the top right solenoid is energized. The oil flow through top section

of the attachment control valve is similar to the retract function but the oil flow to the cylinder is reversed. Oil

pressure unseats the ball check in the counterbalance valve on the head end and forces the rod out of the

cylinder. The cylinder extends and raises the attachment.

The maximum pressure in all the circuits of the attachment control valve is controlled by the maximum

discharge of the pump which is 3300 psi (22753.5 kPa).

f. Carriage Tilt System. The carriage tilt function is also controlled by the electric joystick and the

attachment control valve. Hydraulic oil from the piston pump flows through the control valve the same as for

the above attachment system.

Move the electric joystick to the left and the second from the top right solenoid is energized. The solenoid

allows pilot oil to flow through the solenoid and push the spool in the second section towards the left of the

machine. Oil flows through the second section, pilots open a load compensating check valve and flows from

the work port to the rod end ports of both carriage tilt cylinders. The load compensating check valve operation

is the same as described in the attachment system. Oil pressure unseats the ball check in the counterbalance

valve on the rod end and pushes the cy1inder piston in each cylinder. Oil in the head end of the cylinder flows

from the head end port and back to the attachment control valve. The cylinder retracts which raises the fork

tips. Oil from the tilt cylinders is directed to the attachment control valve return circuit and back to the

hydraulic reservoir through the hydraulic filter.

If the electric joystick is moved to the right, the second from the top left solenoid is energized. The oil flow

through the second section is similar to the fork tips raise function but the oil flow to the tilt cylinders is

reversed. Oil flows to the head end of the tilt cylinders and pilots open the counterbalance on the rod end of

the cylinders. Oil is allowed to flow from the rod end and back to the return circuit of the attachment control

valve. The cylinders extend and lower the fork tips.

A port relief valve set at 4000 psi (27580 kPa) is connected to the rod end of the tilt cylinders. The relief valve

protects the hydraulic lines from bursting when shocks or spikes are encountered on the rod side of the

cylinder.

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