Lift Circuit (Down) - Toro 30821 Service Manual

Lift Circuit (Down)

Lower Cutting Units
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.
During conditions of not lifting or lowering cutting units,
flow from the gear pump is by- passed through the pow-
er steering valve, 2- spool lift/sidewinder valve, and hy-
draulic manifold directly to the hydrostat and the charge
relief valve. Flow then returns to gear pump (P1) inlet.
When the cutting units are to be lowered, the 2- spool
valve is positioned by moving the cutting unit shift lever
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
Groundsmaster 3500- D
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.
The logic cartridge valve (LC1) in the manifold block
maintains 250 PSI (17.2 bar) back pressure on the lift
cylinders. This counterbalance pressure transfers cut-
ting unit weight to the machine to improve traction.
Page 4 - 19 Hydraulic System (Rev. G)