Useful Pump Data
  • Effect of Small Change of Pump Speed
    1. The capacity varies directly as the speed.
    2. The head varies as the square of the speed.
    3. The break horsepower varies as cube of the speed.

  • Effect of Small Change of Impeller Diameter
    1. The capacity varies directly as the diameter.
    2. The head varies as the square of the diameter.
    3. The break hoarse power varies as the cube of the diameter.

  • Effect of Specific Gravity
    Break hoarse power varies directly with specific gravity. If the liquid has a specific gravity other than water (1.0) multiply the break HP for water by the specific gravity of liquid to be handled.

    A centrifugal pump will always develop the same head in feet no matter what the specific gravity of the liquid pumped. However, the pressure (In pounds per square inch) will be increased or decreased in direct proportion to the specific gravity.

  • Effect of Viscosity
    Viscous liquid tend to reduce capacity pump capacity, head and efficiency and to increase pump break hourse power and increase pipe line friction. Consult manufacturers for recommendation when pumping viscous liquids.

  • Effect of Altitude
    Suction lift data are based on values at sea level. Therefore, above sea level the total suction lift must be reduced.

  • Effect of Hot Liquids
    Hot liquid vaporize at higher absolute pressures than cold liquids, therefore the suction lift must be reduced when handling hot liquids with a high vapor pressure or a high temperatures the liquid must flow to the pump suction under pressure.

  • Selection of pumping Unit
    In order to select appropriate pump the following data is essential.
    1. Capacity required in term of L.P.H. or G.P.H.
    2. Discharge head, i.e. highest level up to which water is to be supplied + friction loss, if any.
    3. Suction lift, i.e. lowest water level from which water is to be drawn.

    If the source of supply is a well, following information should be available:
    1. Diameter in case of tube well)
    2. Standing water level.
    3. Lowest water level while pumping and in summer. It is also desirable to ascertain the yield of the well to ensure that pump capacity matches with the yield.

  • Some useful data on selection of Pump
    In cites, every individual person consumes app. 150 to 200 lit per-day. In village, it may be assumed to be 40 to 60 lit per persons per day.

Other data of consumption of water.

Animal Consumption
Horse 50 liters per day
Milk Cow 140 liters per day
Sheep 10 liters per day
Poultry (Per 100) 20 liters per day
  • Height of an average story can be assumed to be 10' to 12'.
  • To find the capacity (in gallons) of an overhead tank. Multiply the length by the width by depth in feet. This will give the volume in cubic feet. Multiply this volume by 7.5 to get capacity in U.S. gallons.

Formulas and Conversions Factors

Pipe velocity (ft. per second)  = 40 x G.P.M. = 321 x G.P.M.

(pipe diameter)2 pipe area


Velocity head (feet) = 321 x G.P.M.

pipe area


Water horsepower = G.P.M. x head in ft. x specific gravity



Break horsepower (Pump) = G.P.M. x head in ft. x specific gravity

3960 x pump efficiency


Efficiency (pump)  = G.P.M. x head in ft. x specific gravity = W.H.P.

3960 x B.H.P. B.H.P.