Lift Circuit (Down) & Counterbalance - Toro Groundsmaster 3500 30807 Service Manual

Lift Circuit (Down) & Counterbalance
Lower Cutting Units
The gear pump (P2) is directly coupled to the hydrostat
through gear pump (P1) and driven by the engine. It sup-
plies hydraulic pressure for operating the power steer-
ing system, raising and lowering the cutting units,
operating the sidewinder unit, and replenishing the
closed loop traction circuit (charge pressure). The pump
takes its suction directly from the hydraulic tank.
During conditions of not lifting or not lowering cutting
units, flow from the gear pump (P2) is by- passed
through the power steering valve, 2- spool lift/sidewind-
er valve, and hydraulic manifold directly to the hydrostat
and the charge relief valve. Flow then returns to the gear
pump inlet and hydraulic tank.
Circuit operation for lowering the cutting units is similar
to raising them. However, pressure is relieved from the
lift cylinders, and this action allows them to lower.
When the cutting units are to be lowered, the 2- spool
valve is positioned by moving the cutting unit shift lever
Groundsmaster 3500
to LOWER. Pressure from gear pump (P2) is used to
shift the pilot valve in the 2- spool valve. This shifting of
the pilot valve allows hydraulic pressure to relieve from
the cap end of the lift cylinders. Flow from the cap end
of the lift cylinders causes the cutting units to lower. At
the same time, the fluid relieved from the cap end of the
lift cylinders goes into the rod end of the cylinders and
back through the hydraulic manifold to the hydrostat.
When the cutting unit shift lever is released, spring ac-
tion returns and detents the valve into the float position
while by- passing flow back to the hydrostat. The pilot
valve remains shifted to allow the lift cylinders to float un-
til the lift control valve is moved to the raise position.
Counterbalance
The logic cartridge valve (LC1) in the manifold block
maintains 250 PSI (17.2 bar) back pressure on the lift
cylinders. This back pressure (counterbalance) trans-
fers cutting unit weight to the machine to improve trac-
tion and minimize turf marking by the cutting decks.
Page 5 - 25 Hydraulic System