Hydraulic Flow Diagrams; Hydraulic Flow Diagrams; Traction Forward And Reverse - Toro Greensmaster 3150 Service Manual

Hydraulic Flow Diagrams

Traction Forward and Reverse

Forward
The hydrostat is driven directly by the engine. The trac-
tion circuit of the hydraulic system acts essentially as a
closed loop. Taking its suction directly from the return
side of the wheel motors of the traction circuit, the hy-
drostat supplies oil flow to the wheel motors through the
supply side of the traction circuit.
With the engine running and traction pedal in the neutral
position, the hydrostat supplies no flow to the wheel mo-
tors. When the traction pedal is pressed to the forward
position, the linkage from the pedal positions the swash
plate in the hydrostat so oil flows out the top port of the
pump. Oil flow out of the top port goes to the wheel mo-
tors and turns them in the forward direction.
Oil flowing out of the wheel motors returns to the bottom
port of the hydrostat and is continuously pumped out the
top port.
Hydraulic oil is supplied to the traction circuit from the
gear pump (P2) though the steering control valve and
back through the charge circuit check valves. This oil re-
places oil losses from flow through the internal case
drain, internal bleed valve, and small amounts of leak-
age. Charge circuit pressure is maintained by the
charge relief valve (R4) that is attached to the hydrostat
back plate.
Hydraulic System
Reverse
The traction circuit operates essentially the same in re-
verse as it does in the forward direction. However, the
flow through the circuit is reversed.
With the engine running and traction pedal in the neutral
position, the hydrostat supplies no flow to the wheel mo-
tors. When the traction pedal is pressed to the reverse
position, the linkage from the pedal positions the swash
plate in the hydrostat so oil flows out the bottom port of
the pump. Oil flow out of the bottom port goes to the
wheel motors and turns them in the reverse direction.
Oil flowing out of the wheel motors returns to the top port
of the hydrostat and is continuously pumped out the bot-
tom port.
The charge circuit functions the same in reverse as it did
in the forward direction.
Traction Circuit Cooling
The traction circuit is cooled by a bleed off circuit in the
hydrostat. The bleed off circuit includes an internal bleed
valve which allows about 1 gpm of hydraulic oil to pass
from the reverse side of the hydrostat while operating
the traction unit in the forward direction. The internal
bleed valve closes when operating the traction in the re-
verse direction.
Note: The bleed valve threads into the hydrostat back
plate. Access to the bleed valve requires removal of the
back plate from the hydrostat.
Note: While operating the traction unit in the reverse
direction under light loads, a slight surge in ground
speed may be experienced.
Rev. A
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