ITT Flygt Rental Guide - Water Solutions

Pumping Definitions
Pumping is the addition of energy to a fluid, which is used mainly for the
purpose of moving the fluid from one point to another.
Centrifugal Pumps
One which transfers energy to the liquid by means of an impeller; i.e. “a
rotating device equipped with suitable vanes”. (The liquid is therefore
delivered in a continuous and uninterrupted flow).
Positive Displacement Pumps
One which transfers energy to a liquid by means of a reciprocating piston,
or similar device, giving an intermittent or “pulsed flow”.
Ejector or Jet Pumps
By mixing a high speed drive medium with a low velocity pumped
medium, an energy exchange is achieved converting velocity energy into
pressure, giving a continuous flow.
Q= Capacity or Volume
H= Total Head
Total Head= Static Head + Friction loss head.
Static Head
The head against which the pump must work when the liquid is stationary.
Friction loss head
The head generated by friction of moving liquid, against the walls of the
discharge pipes.
P= Pump total pressure in metres.
Net Positive Suction Head (npsh)
Energy from an outside source i.e. static head or atmosphere pressure
required to ensure liquid enters the pump volute.
Cavitation
Cavitation occurs when there is insufficient n.p.s.h. i.e., too low a suction
pressure induces cavitation. This causes erosion to the metal surfaces due
to the vapour bubble collapsing, allowing the liquid to rush into the
subsequent spaces at high velocity, thus creating a water hammer effect.
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