That gravel sound is bubbles destroying your impeller — check your NPSH margin free in 30 seconds.
NPSH available vs required for a general water pump installation — pressure, static head, friction and vapor pressure in, cavitation verdict out.
NPSH available vs required for a boiler feedwater pump taking suction from a deaerator — pressure, static head, friction and vapor pressure in, cavitation verdict out.
NPSH available vs required for a fire pump drafting from a static tank or reservoir — pressure, static head, friction and vapor pressure in, cavitation verdict out.
NPSH available vs required for an irrigation pump lifting from a well, river or pond — pressure, static head, friction and vapor pressure in, cavitation verdict out.
NPSH available vs required for a condensate return pump on a hotwell or receiver — pressure, static head, friction and vapor pressure in, cavitation verdict out.
NPSH available vs required for pump installations at elevation (hills, mines, mountain sites) — pressure, static head, friction and vapor pressure in, cavitation verdict out.
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