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High pressure sluice water pump problems

Q: I am having some problems with a high pressure sluice water pump in the bottom ash system. It is used to syphon bottom ash from a hopper into a slurry tank. It is an axially split, single-stage, double-suction, 700 hp centrifugal pump. The system is manually operated. During the last part of the ash pull, the amps drop from a normal level of 70 to 50. At that time, the pump experiences high vibration and the outboard bearing (oil lubricated) goes above 200ºF. The operators tell me that at that time, the solids have all been removed from the hopper, and since there is no water level in the tank above, the pump is essentially pulling air. Can this air be causing the pipe to air lock (no flow conditions), essentially deadheading or hammering the pump? If this is the case, the easy solution is to provide the tank with level control to ensure the pump is always pulling either a slurry or straight water. I am not sure if that is the problem.

A: Pumps are designed to pump liquids. When a pump is operated dry, all bets are off, and the pump will self-destruct prematurely through high vibration levels and resultant bearing and seal problems. Before you worry about anything else, I would strongly recommend that you ensure that the pump is always pumping a liquid. After that, you will then be in a position to isolate and identify any other challenges that might be occurring. Sometimes the “easy solution” will indeed work.

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