Pump Rental Booklet - Catalog - Page 147
Limits On Suction Use
There are a number of factors that effect the suction performance of a
pump attributed to the system dimensions and liquid characteristics.
These are briefly listed as follows and care should be taken to collate the
relative data in order that the technical department have all the pertinent
information.
Pressure On Liquid-Free Surface To Be Drawn Into The Pump
The reservoir from which the liquid is drawn may not always be at
atmospheric pressure – it could be at an elevated pressure or under
vacuum in a closed vessel
Vapour Pressure
Hydro-carbon mixtures or liquids at elevated temperatures and
pressures which create surface evaporation will reduce suction
performance
Liquid Density
Increasing density reduces suction performance
Viscosity And Friction Losses
These also reduce suction performance
Flooded Suction/Suction Lift
Flooded suction will assist the pump’s suction performance,
conversely, suction lift will subtract
The above data is necessary to calculate the Nett Positive Suction Head
available in a system (NPSHa).
The pump itself imposes a restriction on the suction lift by virtue of
its design and the liquid flow characteristics through the pump. This is
referred to as the Nett Positive Suction Head required (NPSHr).
For a pump to sustain a throughput without cavitation, NPSHa must be
greater than or equal to the NPSHr.
