Lift Circuit - Toro Reelmaster 3550-D Service Manual

Lift Circuit: Lower
The tandem gear pump is directly coupled to the vari-
able displacement piston pump/hydrostat which is belt
driven by the engine. The rear section of the tandem
gear pump (P2) supplies hydraulic flow for the steering
circuit, for raising and lowering the cutting units and for
the traction charge circuit. The gear pump takes its suc-
tion from the hydraulic tank. On Reelmaster 3550−D
machines, the oil flow from gear pump (P2) moves
through the steering circuit first, then through the lift cir-
cuit. To provide separate relief pressures for each circuit
on Reelmaster 3555−D/3575−D machines, the oil flow
from gear pump (P2) moves through the lift circuit first,
then through the steering circuit.
The maximum steering circuit pressure of 1000 PSI (69
bar) is limited by the relief valve located in the power
steering valve. On Reelmaster 3550−D machines, the
maximum lift circuit pressure is also controlled by the re-
lief valve located in the power steering valve. Due to the
increased size and weight of the cutting units on Reel-
master 3555−D/3575−D machines, the maximum lift cir-
cuit pressure of 2000 PSI (138 bar) is controlled by an
additional relief valve located in the lift control manifold.
Lift circuit pressure can be monitored at the test fitting in
lift control manifold port G.
The lift control manifold includes four (4) electrically op-
erated solenoid valves. Solenoid valve S1 causes circuit
flow to by−pass the lift cylinders when de−energized
and directs flow to the cylinders when energized. Direc-
tional solenoid valve S2 is used to direct oil flow to raise
the cutting units when energized and lower them when
de−energized. When energized, solenoid valve S3 al-
lows hydraulic flow to and from the front cutting unit lift
cylinders (#1, #4 and #5) and prevents oil passage to
and from these lift cylinders when de−energized. When
energized, solenoid valve S4 allows hydraulic flow to
and from the rear cutting unit lift cylinders (#2 and #3)
and prevents oil passage to and from these lift cylinder
when de−energized.
While operating the machine during conditions of not
raising or lowering the cutting units (joystick in the neu-
tral (center) position), all of the lift manifold solenoid
valves (S1, S2, S3 and S4) are de−energized. Flow not
required for lifting or steering is made available for the
traction charge circuit. Flow in excess of charge circuit
needs then returns to the gear pump inlet.
The console joystick is used to raise and lower the cut-
ting units. The joystick acts as an input to the Toro Elec-
tronic Controller (TEC) which sends electrical outputs to
the appropriate lift control manifold solenoid coils in or-
der to raise or lower the cutting units.
Reelmaster 3550−D/3555−D/3575−D
When the reel enable/disable switch is in the DISABLE
position, the cutting unit lift and lower operation is under
complete control of the joystick (momentary control) and
the cutting units move up or down only as long as the joy-
stick is held in position.
When the reel enable/disable switch is in the ENABLE
position, the cutting unit lower operation is controlled by
the TEC (sequential control). Momentarily "bumping"
the joystick forward lowers the cutting units to the full
down or "Mow" position.
Lower Cutting Units
The operator must be in the operator seat and the mow/
transport switch must be in the MOW position in order
to lower the cutting units. The cutting units will not lower
if the mow/transport switch is in the TRANSPORT posi-
tion.
When the joystick is moved to the lower position by the
operator, solenoid valve S1, S3 and S4 are energized by
the Toro Electronic Controller (TEC). To allow the front
cutting units to be lowered before the rear cutting units,
the controller slightly delays energizing solenoid S4 af-
ter the joystick is moved. The energized solenoid valves
direct gear pump oil flow to the cap end of the lift cylin-
ders. Flow control orifices in the lift control manifold
(OR2, OR4, OR6 and OR8) are bypassed when lower-
ing the cutting units.
Hydraulic pressure along with cutting unit weight causes
the lift cylinder shafts to extend, and lower the cutting
units. Flow control orifices in the lift control manifold
(OR1, OR3, OR5 and OR7) control the cutting unit low-
ering speed by providing a restriction for the return flow
from the lift cylinders.
Because cutting unit weight assists in extending the lift
cylinders when lowering the cutting units, less hydraulic
pressure is necessary during the cutting unit lowering
operation. Lift circuit relief valve (RV) allows lift circuit
pressure to be limited to 500 PSI (34 bar) while lowering
the cutting units. The lift cylinders and cutting units stop
lowering when solenoid valves S1, S3 and S4 are de−
energized.
NOTE: Adjustment of the lift control manifold lift circuit
relief valve (Reelmaster 3550−D = RV1) or (Reelmaster
3555−D/375−D = RV2) is not recommended.
Page 4 − 23 Hydraulic System