How long to boil the water?  If your 30 HP pump is, say, 70% efficient, that means about 30% of the input power goes to heating the water -- not a problem as long as the water is once-through.  Closing the discharge valve confines a small volume of water in there, plus runs the efficiency down very low.  Together, you can get boiling.Input power is much lower at dead-head, but so is efficiency.  Even if it's only drawing 5 HP from the motor, you might have half of that (or more) going to water heating, the rest goes to moving the water from inlet to outlet and back again.  Half of 5 HP is 1.9 kW, and if you only have about a gallon of water in the pump housing it will rise almost 13

2011-08-05

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