Hyundai HX145LCR Manual page 177

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2. BOOM DOWN OPERATION

When the right control lever is pushed forward, the boom 1 spool in the main control valve is moved

to the down position by the pilot oil pressure from the remote control valve.

The oil from the A2 pump flows into the main control valve and then goes to the small chamber of

boom cylinders. At the same time, the oil from the large chamber of boom cylinders returns to the

hydraulic tank through the boom 1 spool in the main control valve.

When the down speed of boom is faster, the oil returned from the large chamber of boom cylinder

combines with the oil from the A2 pump, and flows into the small chamber of the cylinder.

This prevents cylinder cavitation by the negative pressure when the A2 pump flow can not match the

boom down speed. And the excessive pressure in the boom cylinder rod side is prevented by the

relief valve.

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