Types of pumps
There are many pump classifications. One classification is according to the
method energy is imparted to the liquid: kinetic energy, or positive displacement.
A centrifugal pump is of kinetic energy type - it imparts energy to a liquid by means
of centrifugal force produced by a rotating impeller. A positive displacement pump
imparts energy by mechanical displacement. Piston, diaphragm, plunger, screw,
vane, and gear pumps are some examples.
Centrifugal pumps are widely-used because of its design simplicity, high
efficiency, wide range of capacity and head, smooth flow rate, and ease of
operation and maintenance. (Displacement pumps are of lower flow range and
have pulsating flow rate).
Types of centrifugal pumps?
Centrifugal pumps can be grouped into several types using different criteria such
as its design, construction, application, service, compliance with a national or
industry standard, etc. Thus one specific pump can belong to different groups and
oftentimes this becomes descriptive of the pump itself. Some of these groups are:
Based on compliance with industry standards:
ANSI pump - ASME B73.1 specifications
API pump - API 610 specifications
DIN pump - DIN 24256 specifications
ISO pump - ISO 2858, 5199 specifications
Nuclear pump - ASME specifications
UL/FM fire pump - NFPA 20 specifications
Based on number of impeller/s in the pump:
Single stage - pump has one impeller only; for low head service
Two-stage - pump has two impellers in series; for medium head service
Multi-stage - pump has three or more impellers in series; for high head service
The number of impellers, not the number of volutes, determines the number of
stages. Thus a pump with 4 volutes but only 3 impellers is normally referred to as
a 4-stage pump destaged to 3-stage, or 4/3-stage.
Based on impeller suction:
Single suction - pump with single suction impeller (impeller has suction cavity on
one side only); simple design but impeller is subjected to higher axial thrust
imbalance due to flow coming in on one side of impeller only.
Double suction - pump with double suction impeller (impeller has suction cavities
on both sides); has lower NPSHR than single suction impeller. Pump is
considered hydraulically balanced but is susceptible to uneven flow on both sides
of impeller if suction piping is not done properly.
In a pump with more than one impeller the design of the first stage impeller
determines if the pump is considered single or double suction type.
Based on type of volute:
Single volute - pump volute has single lip which is very easy to cast. Is usually
used in small low capacity pumps where a double volute design is impractical
due to relatively small size of volute passageway which make obtaining good
quality commercial casting difficult. Pumps with single volute design have higher
Double volute - pump volute has dual lips located 180 degrees apart resulting in
balanced radial loads; most centrifugal pumps are of double volute design.
Based on nozzle location:
End suction/top discharge - the suction nozzle is located at the end of, and
concentric to, the shaft while the discharge nozzle is located at the top of the case
perpendicular to the shaft. Pump is always of an overhung type and typically has
lower NPSHR because the liquid feeds directly into the impeller eye.
Top/top nozzles -the suction and discharge nozzles are located at the top of the
case perpendicular to the shaft. Pump can either be overhung type or
between-bearing type but is always a radially-split case pump.
Side/side nozzles - the suction and discharge nozzles are located at the sides of
the case perpendicular to the shaft. Pump can either be an axially or radially split
Based on shaft orientation:
Horizontal - pump with shaft in horizontal plane; popular due to ease of servicing
Vertical - pump with shaft in vertical plane; ideal when space is limited or of a
premium, or when pumping from a pit or underground barrel to increase the
Based on orientation of case-split:
Axial split - pump case is split axially; the upper half is called the upper or top
case, the lower half is called the lower or bottom case. The case cannot be
supported at shaft centerline because of the case split; is usually limited to
temperature up to 450 degrees F to avoid misalignment because of uneven
thermal expansion from shaft centerline. The flat case gasket and irregular bolting
pattern makes containing the bolt stress difficult hence it is limited in its
hydrostatic test and allowable working pressure.
Radial split - pump case is split radially; the split parts are usually referred to as
case and cover; can be supported at shaft centerline for even thermal expansion
and is the preferred construction for high temperature application. The confined
case gasket and circular bolting pattern makes containing the bolt stress more
manageable hence it can be designed for higher hydrostatic test and allowable
Based on bearing support:
Overhung - the impeller overhungs on one end of shaft which is unsupported by a
bearing; usually has lower NPSHR because there is no shaft blockage at the
impeller eye. The trade-off is that pump has higher shaft deflection.
Between-bearing - the shaft has bearing support on both ends, thus impeller is
located in between-bearings. Pump has lower shaft deflection than overhung
pump but usually has higher NPSHR because shaft is blocking the impeller eye
and shaft diameter at the impeller is usually of larger size.
Based on shaft connection to driver:
Close-coupled - the impeller is mounted on the driver shaft which is of special
design. This is also known as integral shaft design. Typically used for light
service. The pump-driver assembly is very compact, lightweight, and inexpensive.
Direct-coupled - the pump and driver have separate shafts connected by a flexible
coupling. Usually a spacer coupling is used to allow the removal of seals without
disturbing the driver.