Shibaura SG280E, Workshop Manual

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2. Oil flow when driving forward
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When the HST pedal is pressed forward, the variable pump operates and discharges oil.
The high-pressure check valve is closed by hydraulic oil. The low-pressure side is opened by charge pressure.
Although the check valve is open in the neutral position, as the circuit pressure increases while the mower is
powered, the high-pressure valve port gradually closes. This allows smooth acceleration.
When the pedal is returned to the neutral position, reversal of the load pressure causes the valve to return
quickly to neutral position. This allows the gradual closing of the valve for a smooth stopping feeling.
Although the high-pressure relief valve is normally closed, it is triggered when excessive load occurs on the
output shaft of the motor and the pressure inside the HST circuit reaches 20.58Mpa (210kgf/cm
2
) or more. This
prevents damage to various parts.
Oil passing through the relief valve flows into the low-pressure side of the circuit.
Fig.5-3-7
Check/ Relief valve Check/ Relief valve
Check/ Relief valve