Twin Disc MG-5170DC, Service Manual

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Twin Disc, Incorporated
Operation
Marine Transmission Service Manual #1020667
Hydraulic System with Manual Control Valve
The oil pump draws oil through the strainer from the oil sump and discharges it
through the oil filter. Filtered oil enters the control valve through the inlet port.
The incoming oil forces the pressure regulator piston against the springs to
open the path to the lubrication circuit. Oil not used for clutch engagement
flows past the regulator piston to become lubrication oil. Lubrication oil flows
through the heat exchanger to the lubrication oil circuit in the transmission to
lubricate and cool the clutches and bearings. There is a lubrication oil pressure
relief valve to limit maximum lubrication oil pressure to approximately 690 kPa
(100 psi).
In Neutral, the inlet port of both clutches is connected to the atmosphere.
Since the area behind the clutch pistons is open to sump, the clutches are
disengaged. Oil is distributed through the lubrication system. The area between
the pressure regulating piston and the rate-of-rise piston is connected to
sump at all times to prevent any leakage oil from affecting the pressure
regulation.
When the control valve is shifted to engage either clutch, the valve directs
main pressure to engage the selected clutch pack. Oil is also directed to move
the rate-of-rise piston, compressing the pressure regulator springs. This
progressively increases the clutch engaging pressure causing the clutches to
engage at a controlled rate.
The control valve allows only one clutch to be engaged at a time, and the oil
from the disengaged clutch is vented to sump (atmospheric pressure). The
clutch return springs move the disengaged clutch’s piston to the disengaged
position minimizing clutch plate drag.