Heat Generation In The Pump


Every day salesmen call on customers and make claims that their pump or mechanical seal can take more heat than the other guys. Before we rush out to purchase these wonder products we should take a closer look at the heat problem. The heat comes from several sources:

  • Generated at the seal faces or by packing rubbing against the shaft or sleeve
  • Ambient conditions. The weather or atmosphere surrounding the pump.
  • The product contains a certain amount of heat
  • Two parts rubbing together that are not supposed to be rubbing can generate a lot of local heat.
  • Grease seals. They rub against the shaft very close to the bearings.
  • Running to the left of the best efficiency point (BEP) means that the discharge is restricted.
  • Friction of the pump rotating parts, especially if the discharge is throttled.

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 Gravity

S.H. = 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