A wide range of pumps are available for most applications. In selecting a pump the following criteria should be considered:

• Flow: Rate at which the pump will deliver, measured in gallons/hour (gph), gallons/min (gpm); litres/hour (l/h) or litres/min (l/m).
• Head: Maximum height to which the pump will deliver (neglecting piping friction losses). This is also a measure of the pump's pressure.
• Suction Lift: Needed where the water source is lower than the pump. Some pumps are not self-priming and need to be below the water source to be fed by gravity.
• Total Head: This is the entire vertical distance from water source to the tank.
• Horizontal Distance: Pumps cannot move water very far by suction, even if the lift involved is below it's limit. So if large distances from source to tank are involved the pump is normally located at the supply and the water pressure used. Adequate wiring must then be used to compensate for voltage drop. Large diameter pipes will minimise losses due to pipe friction. For large distances particularly if large volumes of water are required the simplest route may be to use standard 230 Vac pumps run from an inverter.
• Power Consumption: Not the least important consideration in a remote power system!

Flow, Head, Pressure & Power Consumption are all related: for the same pump, the greater the lift the lower the flow and the more power used.

Useful Formulae

• head in ft. = 2.31 x pressure in psi. {pounds/sq. inch}
• head in metres = 10 x pressure in bar {kg/sq m}
• Typical household water pressure runs at between 10 & 40 psi.
• 10 psi = 0.69 bar (kg/sq cm)
• 1 bar = 14.5 psi
• 1 l/m = 0.22 gpm = 13.25 gph
• 1 gpm = 4.45 l/m
• 1 US gallon = 0.83 UK gallon.

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