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07 Pumps and Pumping

Definitions and descriptions

Absolute pressure

The gauge pressure, plus the pressure of the atmosphere. (When a pressure is referred to without ‘gauge’ or ‘absolute’ being stated, it is normally understood to be the gauge pressure).

Atmospheric pressure

Normal atmospheric pressure at sea level is 1.00 bar = 10.20m head.
Atmospheric pressure varies with the altitude above sea level and with the weather conditions.


All pipework, pipe fittings, radiators, etc. will create a resistance to the flow of water through them. The more or faster you try to circulate water through them, the more resistance they will create to this flow.

Water, like electricity, will always try to take the least line of resistance. To overcome this resistance, a force must be put into the water. That force will overcome resistance and circulate the water. This force is pressure.

Compiled and published by: The Institute of Plumbing
  Last revision: 2002
  Edition: 1
  Number of pages: 8
  Format: PDF