1900 Series Horizontal Splitcase Pumps
Instruction and Repair Manual
10
11/12/18
NET POSITIVE SUCTION HEAD (NPSH):
NPSH can be defined as the head (energy) that causes liquid to flow through the suction pipe and enter the eye of the
impeller.
NPSH is expressed in two values:
1. NPSH required (NPSHR).
2. NPSH available (NPSHA).
It is essential that NPSHA always be greater than NPSHR to prevent cavitation, vibration, wear and
unstable operation.
NPSHR is a function of the pump design and therefore varies with the make, size, capacity and speed of the pump. The
value for your pump can be obtained from your pump performance curve or the factory.
NPSHA is a function of your system and may be calculated as follows:
A. When the source of liquid is above the pump:
1. NPSHA = barometric pressure (feet) + static suction head (feet)* – friction losses in suction piping (feet)
– vapor pressure of liquid (feet).
B. When the source of liquid is below the pump:
1. NPSHA = barometric pressure (feet) static suction lift (feet)* – friction losses in suction piping (feet)
– vapor pressure of liquid (feet).
*The datum elevation plane for horizontal pumps is the pump centerline.
WET WELL DESIGN:
Generally, it is required that an evenly distributed flow of non-aerated water be supplied to the pump suction. Improper
wet well or sump design or insufficient suction pipe submergence can result in intake vortexing which reduces the
pump’s performance and can cause severe damage to the pump.
We recommend that you secure the advice of a qualified Consulting Engineer for the analysis and design of the wet well.
Significant engineering data on wet well design is provided in the Hydraulic Institute Standards.
Upon request, Fairbanks Nijhuis™ will review plans and give general comments on the installation, but will not approve
such plans for a specific installation and will accept no responsibility or liability for the performance of the pump
intake structure.
LOCATION AND HANDLING:
The pump should be installed as near the fluid as possible so a short direct suction pipe can be used to keep suction
losses at a minimum. If possible, locate the pump so the fluid will flow to the suction opening by gravity. The discharge
piping should be direct and with as few elbows and fittings as possible. The total net positive suction head available
(NPSHA), which includes the suction lift and pipe friction losses, must be greater than the net positive suction head
required (NPSHR) by the pump.
The pump and driver should be located in an area that will permit periodic inspection and maintenance. Head and access
room should be provided and all units should be installed in a dry location with adequate drainage.
