Friction Within The Pump

FRICTION WITHIN THE PUMPĀ F038

No pump is 100% efficient.

If a pump is rated 60% efficient that means that 40% of the power is doing something other than moving liquid, and it turns out a lot of it is being converted to heat.

In a normal temperature stabilized pump, running at its best efficiency point (BEP), the temperature rise within the pump is calculated from the following formulas:

BHP = Brake Horse Power (you get his number from the pump curve supplied by the manufacturer

42.41 = Conversion of HP to btu./min.

lbs./ min. = gpm. x 8.33 x specific ravity

Specific Heat =(1 for water)

BKW = Brake Kilowatts ( From the pump curve)

14.34 = Conversion of Kilowatts to Kilocalories

A temperature rise across the pump of 18 degrees Fahrenheit or 10 degrees Centigrade is considered excessive. This can occur if the pump is run with a shut, or excessively throttled discharge. If you would like to calculate the temperature rise of the liquid in a running pump when the discharge is shut, use the following formulas :

Temperature rise in degrees Fahrenheit per minute equals:

  • BHP. = Brake Horse Power at shut off
  • 42.4 = Conversion from Brake Horse Power (B.H.P.) to BTU/ minute
  • W = Net weight of the liquid, in the pump, in pounds (lbs.)
  • C = Specific Heat of the liquid
  • Temperature rise in degrees Centigrade per minute equals:
  • BKW. = Brake Kilowatt at shut off
  • 7.97 = Conversion from Brake Kilowatts (BKW) to Kilo calories/ minute
  • W = Net weight of the liquid, in the pump, in kilograms (Kg.)
  • C = Specific Heat of the liquid

There are other sources of heat you must also consider:

Heat from the ambient conditions

  • If pipes, pumps, valves and other types of equipment are placed next to hot boilers or exposed to extreme changes in weather, we will have to consider this addition or removal of heat in troubleshooting temperature related problems.

Heat in the product its self

  • All fluids are processed at some temperature range. It is this heat that we will be adding to, or subtracting from. Many fluids are pumped close to the temperature at which they will vaporize, solidify, coke, crystallize etc.
  • It is critical that you determine the desired operating range for the fluid before you make any attempt to alter it.

Heat generated by parts rubbing together

  • Rotating parts rub against stationary parts when the pump shaft experiences deflection or you have excessive pipe strain.

Heat generated by the bearing seals

  • These seals add heat at the worst possible location. Grease or lip seals will also cause shaft wear at the point the seal material touches the rotating shaft.

Heat generated by the packing or mechanical seal

  • See “Seal face heatĀ generation” for a detailed explanation of this heat source.

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Posted

  • On February 15, 2018