Lift Circuit - Toro Greensmaster 3120 Service Manual

Lift Circuit

Raise Cutting Units
Lower Cutting Units
Greensmaster 3120
17230SL Rev C
A tandem gear pump is directly coupled to the piston (traction) pump. The rear
gear pump section (P3) supplies hydraulic flow for the steering circuit (priority
flow), for raising and lowering the cutting units and for the traction system charge
circuit. The gear pump takes its suction from the hydraulic tank through a suction
strainer. Maximum circuit pressure of 7998 kPa (1160 PSI) is limited by the
relief valve located in the steering valve.
During cutting unit hold (not raising or lowering) conditions, flow from the rear
gear pump section is by-passed through the steering valve and de-energized
solenoid valve (S2) in the mower manifold directly to the traction system charge
circuit. Charge circuit flow in excess of closed-loop system requirements returns
to the hydraulic tank via the traction (piston) pump case drain.
When the Rasie/Lower Mow control is moved forward, the mower manifold
solenoid valves (S2 and S3) are energized; refer to
solenoid valve (S2) blocks the flow of fluid to the traction system charge circuit,
and directs the flow to energized solenoid valve (S3). The flow continues through
de-energized solenoid valve (S4) and onto the lift cylinders. Hydraulic pressure
at the barrel end of the lift cylinder extends the cylinders causing the cutting units
to raise. At the same time, the cylinder pistons push hydraulic fluid out of the
rod end of the cylinder, through energized solenoid valve (S3) and back into the
traction system charge circuit. Raise speed for the front cutting units is controlled
by a pair or 0.055 inch orifices in the mower manifold. A 0.030 inch orifice in the
mower manifold creates a slight delay in raising the center cutting unit.
When solenoid valves (S2) and (S3) de-energize, spring action returns the
valves to their original position and flow is directed back to the traction charge
circuit stopping lift cylinder movement. The lift cylinders position is held in place
by the check valve feature of de-energized solenoid valve (S4), blocking any
return flow from the cylinders.
When the Rasie/Lower Mow control is moved rearward to lower the cutting units,
mower manifold solenoid valves (S2 and S4) are energized; refer to
Energized solenoid valve (S2) blocks the flow of fluid to the traction system
charge circuit, and directs the flow through de-energized solenoid valve (S3)
and onto the lift cylinders. Hydraulic pressure at the rod end of the lift cylinder
retracts the cylinders causing the cutting units to lower. At the same time, the
cylinder pistons push hydraulic fluid out of the barrel end of the cylinder, through
energized solenoid valve (S4), de-energized solenoid valve (S3) and back into
the traction system charge circuit. Lower speed for the front cutting units is
controlled by a pair or 0.055 inch orifices in mower manifold. An adjustable
flow control valve in the mower manifold creates a slight delay in lowering the
center cutting unit.
Relief valve (R2) in the mower manifold is incorporated into the lowering circuit
in case the cutting units are obstructed during lowering. The relief valve is set
to 1,724 kPa (250 psi) at the factory. Once the cutting units are fully lowered,
solenoid valve (S2) and (S4) de-energize, spring action returns the valves to their
original position and flow is directed back to the traction charge circuit stopping
lift cylinder movement.
Page 4–17 Hydraulic System: Hydraulic Flow Diagrams
Figure 20. Energized
Figure 21.