| 摘要 |
PURPOSE:To enable heating up without providing an additional heater by switching a plurality of hydraulic pumps between onload and unload in accordance with a specific program at the time of starting said pumps. CONSTITUTION:Solenoid valves 8, 9 for switching between onload and unload and a pressure control relief valve 10 are coupled to the delivery sides of plural hydraulic pump 1, 2, and at the time of starting said plural pumps 1, 2, the solenoid valves 8, 9 are on-off controlled is accordance with a specific program. Since the working oil can be heated to a proper temperature by the heat produced from the pressure control relief valve 10, heating up can be performed without requiring an additional heater.
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