Form No. 29703
Note!
When stopping the swing, the torque control/brake valve will provide controlled stopping of the swing. The
controlled stopping will only occur when the joystick is in the neutral position.
When the joystick is returned to neutral, the torque control piston returns to neutral, the control piston returns to
neutral, and the stroking piston is held in position since fluid cannot escape to tank. The momentum of the
upper swinging causes the swing motor to overrun the pump output and pressurize B port. Pressure in the B
port is sent to the torque control valve via ports MB and X6. Pressure shifts the shuttle valve , torque control
piston, and the braking piston. As the torque control piston is shifted, it opens one side of the stroking piston to
tank. The pressure from B port forces the braking piston against the spring and meters the amount of fluid
that can go to tank from the stroking piston. As the pressure drops, the spring will overcome the pressure and
allow the stroking piston to shift more rapidly to neutral. This will allow pressure to rise at B port and continue
to slow the swinging action. Pressure in the pump will also buffer the speed that the swashplate returns to
neutral.
Adjustment of the braking piston will alter the stopping action. Turning the screw in, will increase spring
pressure, and increase the pressure required to overcome the spring. The higher pressure will give a more severe
stopping action. The opposite will occur if the screw is turned out.
FIGURE 39
SWING TOROUE CONTROL VALVE:
(HYDRAULIC FUNCTION)
XI. Swing Circuit
(continued)
The following will cover the hydraulic stopping of the upperstructure swing. Not the mechanical stopping
by means of a brake. A swing parking brake is provided that will be covered separately.
From
Pressure
Reducing
Valve
Cushioning
Adjustment
Brake
Valve
Stroking
Control
Piston
Swing Right
Swing Left
Right
Swing
From Swing
Suction Filter
Torque
Control
Piston
Begin Point/High
Pressure Balance
High
Pressure
SHuttle
Pilot
Shuttle
Max Torque
Adjustment
Stroking
Piston
36
Right Swing
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