Function The hydraulic main pump is the prime power source for excavators. Powered by the engine, it turns mechanical energy into high-pressure hydraulic power and sends pressurized fluid to boom, stick, bucket, track drive and swing motors to drive all machine functions.
Type Axial variable piston pumps are standard equipment on construction excavators. Mid-size and large units come with one-piece dual main pumps and a pilot gear pump installed on the rear housing. This twin high-pressure pump has two independent sections feeding oil to different ports of the main control valve for combined operations, with operating pressure ranging from 28 to 35MPa. The low-pressure pilot pump at the pump end works at 3~4MPa with minimal flow, delivering control fluid for operator levers and main valve spools.
Internal Parts Housing & cylinder block: Multiple pistons rotate with the main shaft to draw in and pressurize hydraulic oil. Changing the swash plate angle adjusts piston travel and overall pump displacement. The external hydraulic regulator moves the swash plate in response to pressure signals. A steeper angle delivers bigger displacement and flow for faster work; a shallower angle reduces fuel burn and prevents engine shutdown under load. The valve plate isolates the intake port and high-pressure outlet to distribute oil evenly.
Three Control Modes Constant power control automatically scales down pump displacement under heavy loads to prevent engine stall and utilize full rated power. LS load sensing delivers oil flow matching real demand and runs at low displacement while idling to save fuel. HP pressure cut-off drops displacement to the minimum once pressure hits the maximum limit, preventing hoses and cylinders from blowing out.
Common Failures Worn pistons or valve plates create internal leaks, and a seized regulator results in slow, underpowered operation. When the regulator sticks at maximum displacement, the engine will be overloaded, emitting black smoke and stalling under heavy work. Major internal leakage converts lost pressure into heat, causing hydraulic fluid to overheat. Air drawn into lines, low fluid level or faulty bearings and pistons will create abnormal pump noise.
Maintenance Change hydraulic oil and filters on schedule to avoid abrasion on key parts. Seal all suction lines tightly to block air intake and machine shake. Maintain proper fluid level to keep the pump in good condition.
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