Head

HEAD H005

This is the term centrifugal pump people use in place of the word pressure. It turns out that “head” is a very convenient term in the pumping business.

Capacity is measured in gallons per minute and each gallon of liquid has weight so we can easily calculate the pounds per minute being pumped. Head or height is measure in feet so if we multiply these two together we get foot- pounds per minute which converts directly to work at the rate of 33,000 foot pounds per minute equals one horsepower.

In the metric system each liter of liquid has weight so we can easily calculate the kilograms per minute being pumped. Head or height is measure in meters so if we multiply these two together we get kilogram meters per minute which converts directly to work at the rate of 610 kgm/min = 1 kilowatt.

If you are more comfortable with metric horsepower units, you should know that 735.5 watts makes one metric horsepower

Pressure is not as convenient a term because the amount of pressure that the pump will deliver depends upon the weight (specific gravity) of the liquid being pumped and the specific gravity changes with the fluid temperature and concentration.

If you will refer to Fig #l you should get a clear picture of what is meant by static suction or discharge head.

Note that we always measure from the center-line of the pump to the highest liquid level

To calculate head accurately we must calculate the total head on both the suction and discharge sides of the pump. In addition to the static head we will learn that there is a head caused by resistance in the piping, fittings and valves called friction head and a head caused by any pressure that might be acting on the liquid in the tanks including atmospheric pressure called ” surface pressure head”.

Once we know these heads it gets simple. We will subtract the suction head from the discharge head and the amount remaining will be the amount of head that the pump must be able to generate at its rated flow.

Please refer to other sections of this CD to learn how to calculate the different types of head:

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  • On February 15, 2018