Cutting Unit Circuit - Toro 30821 Service Manual

Cutting Unit Circuit

Mow
The gear pump (P1) is directly coupled to the the hydros-
tat which is driven by the engine. Taking its suction di-
rectly from the hydraulic tank, the gear pump (P1)
supplies oil flow to the manifold block and to the cutting
unit motors.
Solenoid valve (R1) is de- energized with the engine
running when either the cutting unit drive switch is in
DISENGAGE or the transport/mow slide is in TRANS-
PORT. Solenoid valve (R1) by- passes flow from the cut-
ting unit motors directly to the hydraulic reservoir.
Solenoid valve (R1) is energized with the engine run-
ning when the cutting unit drive switch is in ENGAGE
and the transport/mow slide is in MOW. When ener-
gized, solenoid valve (R1) allows gear pump (P1) flow
out manifold block port M1 to the cutting unit motors.
When solenoid valve (R1) is energized, brake relief car-
tridge (BV) is shifted (opens) to allow oil return from the
cutting unit motors.
Oil flows through the left, right, and then rear cutting unit
motors as it turns the motors. The oil then returns into
manifold block port (M2), the oil cooler, the oil filter and
to gear pump (P1) inlet.
If cutting unit circuit pressure exceeds relief pressure of
3200 PSI (221 bar), solenoid valve (R1) shifts to allow
circuit pressure relief.
Groundsmaster 3500- D
Cutting Unit Blade Braking
When the solenoid valve (R1) is de- energized as the
PTO switch is DISENGAGED, brake relief cartridge
(BV) shifts to its closed position, blocking return flow
from the deck motors and slowing the cutting blades
The inertia of the rotating cutting blades, however, effec-
tively turns the deck motors into pumps causing an in-
crease in pressure as the flow from the motors comes
up against the closed brake relief cartridge (BV). When
this pressure builds to approximately 1500 PSI (103
bar), brake relief cartridge (BV) opens which allows hy-
draulic flow to return to tank and reduces return pres-
sure. When return pressure drops below 1500 PSI (103
bar), brake relief cartridge (BV) reseats to further slow
the cutting blades. This action repeats several times in
a very short time frame as the blades finally come to a
stop. Once the blades have stopped, brake relief car-
tridge (BV) remains closed to keep the deck motors from
rotating.
Page 4 - 15 Hydraulic System (Rev. G)