Overheating and Outrigger Creep Mid-Pour
During a 90 m3 wall pour, the pump has been running for 2 hours. Hydraulic oil temperature reaches 95 degrees C and the warning light is on; the oil cooler fan is not turning. Output falls from 65 m3/h to 30 m3/h. The main pressure gauge fluctuates between 24 and 31 MPa with the relief valve set at 32 MPa. There is a loud whine from the pump. The operator notices the left rear outrigger has crept down about 10 mm in 5 minutes; the boom is extended 30 m and has drifted slowly. The hopper is full. The crew wants to finish the last 12 m3. Ambient temperature is 34 degrees C. The reservoir sight glass is at MIN, and there is no visible external leak. The remote emergency stop was tested at the start of the pour.
1. Identify likely causes and explain the urgency.
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The overheating is likely from the failed oil cooler fan, made worse by low reservoir level and high ambient temperature. The whine and fluctuating pressure suggest cavitation or aeration from low oil, a restricted intake, or pump wear. The outrigger creep and boom drift are the most urgent findings: a holding valve, pilot check valve, or cylinder seal may be bypassing, and the outrigger is losing support under load. Ten millimeters in five minutes is significant, and boom drift means the boom may not stay where it is placed. Continuing the last 12 m3 risks tip-over, boom movement over workers, and hydraulic system damage. The pour must stop.
2. What immediate actions should the operator take?
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Stop pumping and reduce engine speed. Move the boom to a safe, lowered position using the manufacturer's emergency or manual lowering procedure if normal controls are drifting. Keep personnel out from under the boom and away from the outrigger. Do not retract the outrigger under load without following the manufacturer's procedure; secure the machine and barricade the area. Shut down the pump, allow the hydraulic oil to cool, and check the oil level and cooler fan circuit. Notify the supervisor and the contractor that the pour is stopped. Do not add oil blindly or continue pumping to finish the load; find the cause of the outrigger creep and boom drift before any restart.
3. What inspection and repair steps are required before the pump can return to service?
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Inspect the cooler fan motor, fuse, relay, and wiring; clean the cooler core; check hydraulic oil level and condition and look for aeration or contamination. Pressure-test the main relief and pump performance. For the outrigger, inspect the holding valve, pilot check valve, cylinder seals, and hose connections, and load-test the outrigger after repair. For the boom drift, inspect the boom holding valves and control valve spools. Replace filters and correct the low oil level only after finding any loss. A qualified mechanic should verify pressures and holding functions, and the repair should be documented before the pump returns to service. The remaining concrete should be placed with another pump or rejected per the contractor's plan.