Sand Pro 2040Z Page 4 - 11 Hydraulic System
Traction Circuit
The Sand Pro traction system consists of two (2) inde-
pendent unitized pump and wheel motor transmissions
that are belt driven by the engine. The transmissions
provideclosedlooptractioncircuits:onefortheright
wheel drive and one for the left wheel drive. Each of
these transmission circuits include a variable displace-
ment piston pump which provides hydraulic flow for one
wheel motor that drives a rear wheel through a reduction
gear. The swash plate in each of the transmission piston
pumps is controlled by one of the operator motion con-
trol handles. The motion control handles are connected
tothetransmissiontraction levers with a linkage rod and
include integrated dampeners for enhanced traction
control. The transmissions also include an internal
brake used for the machine parking brake.
The angle of the piston pump swash plate determines
pump flow and ultimately traction speed. When a motion
control handle is moved a small amount, a small swash
plate rotation results in low pump output and lower t rac-
tion speed. When the control handle is moved fully, the
pump swash plate rotates fully to provide maximum
pump output flow and traction speed.
Because hydraulic flow to each rear wheel is deter-
mined by control handle movement and subsequent
swash plate position, steering is accomplished by mov-
ing the two control handles a different amount or direc-
tion.
With the engine running and the motion control handles
in the neutral position, the transmission piston pump
swash plates are held in the vertical position, providing
no flow to drive either rear wheel so the machine re-
mains stationary. The tract ion circuit check valves in-
clude an orifice which allows the traction neutral position
to be easier to adjust.
Forward
When a motion control handle is pushed forward, the
rod connected to the control handle positions the swash
plate in t he transmission piston pump to provide oil flow
through the traction circuit. This oil flows to the trans-
mission motor and turns the motor in the forward direc-
tion. Oil flow from the motor returns to the transmission
pump and is continuously pumped as long as the control
handle is pushed forward.
The transmission pumps and motors use a small
amount of hydraulic fluid for internal lubrication. Fluid is
designed to leak across internal transmission parts into
the transmission case drain. This leakage results in the
loss of hydraulic fluid from the closed loop traction cir-
cuits that must be replenished.
A charge pump in each transmission supplies hydraulic
flow for maintaining 29 to 43 PSI (2 to 3 bar) to the low
pressure side of both of the traction circuits. The charge
pump replenishes the closed loop traction circuits with
fluid from the hydraulic reservoir (transmission case).
The charge relief valve in the transmission maintains
sufficient pressure so that charge pump flow is guided
past check valves to the low p ressure sid e of each trac-
tion circuit. Charge pump flow in excess of system re-
quirements is relieved through the charge relief valve
back to the transmission case. The charge pump in the
right side transmission also supplies flow for the
groomer (rear attachment) lift circuit.
Reverse
The traction circuit operates essentially the same in re-
verse as it does in forward.
When a motion control handle is pulled rearward, the
rod connected to the control handle positions the swash
plate in the transmission piston pump to provide oil flow
through the traction circuit. This oil flows to the trans-
mission motor and turns the motor in the reverse direc-
tion. Oil flow from the motor returns t o the transmission
pump and is continuously pumped as long as the control
handle is pulled rearward.
The charge circuit functions the same in reverse as it
does in the forward direction.
1. Transmission (LH)
2. Traction lever
3. Brake lever
4. Bypass valve
Figure 11
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4
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Hydraulic
System
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