Type of pump
The pump's designation does not always provide information on the pump type, as very different criteria are used to designate a pump.
Criteria for pump classification
- Operating principle or function
- Design characteristics (impeller type, impeller arrangement, casing type, installation type)
- Purpose or application (with regard to the pumps' operating mode, use in a pump system, fluid handled)
- Pump material
Operating principle or function
- This type of hydraulic turbomachinery is characterised by the transmission of energy by impeller vanes or blades as they deflect the flow of a fluid (see Fluid mechanics). In contrast, positive displacement pumps are characterised by the displacement of fluid volume.
- The head of a centrifugal pump is proportional to the square of the pump speed (see Affinity laws).
Positive displacement pump
- The operating principle of a positive displacement as utilised by positive displacement pumps is characterised by the periodic change in volume.
- In addition, the expansion action of vapours or gases can be used for displacement purposes (pulsometer, Humphrey pump).
Jet pump (eductor-jet pump)
- The pressure differential in a nozzle created when a motive fluid is directed through it is used to convey a second fluid. The motive fluids can be liquids, gases or vapours.
- As these pumps have no moving parts, their design is extremely simple.
- Their powers and efficiency are limited.
Air lift pumps (mammoth pumps)
- Air lift or mammoth pumps' mode of operation is based on the lift action of a mixture of liquid and gas (see Two-phase flow).
Therefore, they can only be used in pumping stations with sufficient geodetic height differences.
- Hydraulic rams use the kinetic energy of a flowing liquid column by converting it into another form of energy (e. g. pressure energy) via a sudden deceleration action.
- Elevators lift liquids to a higher level without changing their pressure by using bucket wheels, bucket elevators, Archimedean screws (see Archimedean screw pump) and similar devices.
- Electromagnetic pumps' mode of operation depends on the direct action of a magnetic field on the ferromagnetic fluid handled; their application is therefore limited to the pumping of liquid metals.
As each operating principle requires its own fundamentally distinct pump design, categorising pumps according to their design features is only relevant when distinguishing between different pumps which share a common operating principle.
The design differences described below refer to centrifugal pumps.
- Depending on a centrifugal pump's specific speed, its impeller may be a radial, mixed flow or axial impeller .
- Radial and mixed flow impellers can be designed with open (without shroud) or with closed channels (with shroud).
- Axial impellers (propellers) can be cast in one piece with their hubs. The blades (see Vane) can be attached to the hub so as to allow blade pitch adjustment or variable pitch control in order to improve the characteristic curve or enable control during operation (see Impeller blade pitch adjustment).
- The arrangement of the propeller blades does not necessarily have to be perpendicular to the pump shaft (see Propeller pump), especially if the propeller is intended for high heads (while maintaining its design advantages with regard to control) and has to cope with radial (i.e. diagonal) flow velocity as a result.
- In addition, specialised impellers are available for special fluids including the single-vane, two-channel, three-channel or free-flow impeller (see Torque flow pump) and peripheral impeller (see Peripheral pump).
- The impeller of a centrifugal pump can be supported by bearings on both sides or on one side only (overhung).
Using an overhung arrangement eliminates the need for a second shaft seal but increases shaft deflection, all else being equal.
- In the case of high flow rates, a between-bearings impeller can be designed as a double-entry impeller (see Double-suction pump) which also helps to balance the axial thrust.
- High heads can be achieved by a multistage impeller arrangement (see Multistage pump). If axial thrust balancing is required in a multistage arrangement, half of the impellers can be mounted in back-to-back arrangement provided that there is an even number of stages.
- Combinations of double-entry and multistage arrangements are also feasible.
- Most of the distinctive pump design features relate to the wide variety of possible casing types (see Pump casing).
- The various modes of installation involve a whole range of different design features.
- First of all, a distinction is made between centrifugal pumps with horizontal (see Horizontal pumps) and vertical (see Vertical pump) shaft.
- Centrifugal pumps can be installed dry (see Dry installation) or wet (see Wet well installation). Wet-installed centrifugal pumps are also referred to as submersible pumps and are submerged in the fluid handled as are most tubular casing pumps.
- In the past, centrifugal pumps with inclined shafts were sometimes used in low-lift pumping stations.
- A further distinguishing feature is the centrifugal pump's attachment to the foundation. The pump may stand on its own feet (in the case of horizontal pumps with "feet at the bottom of the casing" or "with feet arranged at shaft centreline") or may be flanged to the drive (in the case of close-coupled pumps).
- There are further differences in the way the pump casing is connected to the drive housing (e.g. flanged motors or motor stools/drive lanterns).
- Different baseplate arrangements are possible (combined baseplate for the entire pump set or separate baseplates for pump and motor).
- Finally, a distinction must be made between fixed installation pumps and mobile or portable pumps.
Purpose or application
It is very common to name pumps after their purpose (see Pump application). The operating mode, application or the fluid handled are characteristic features found in the names of pumps which in most cases make their designations self-explanatory.
Mode of operation
- Pumps may be termed main (duty) pumps, stand-by pumps or replacement pumps.
- Main pumps are sometimes supported by a booster pump.
- Other concepts which used to denote the operational duty of a pump include: full load or base load pumps; part load (e. g. half load), low load or peak load pumps; auxiliary, start-up or emergency pumps.
There are many designations which describe the relationship between the pump and the system/plant it serves. The most frequently used designations are listed below:
- Pumps employed in the field of water management (e.g. water supply, irrigation and drainage, as well as waste water disposal) include waterworks, water supply and hydrophor pumps (see Domestic water supply system); deep well and borehole pumps; irrigation and spray irrigation pumps; pumps for low-lift pumping stations, drainage pumps, flood control and stormwater pumps.
- Pumps installed in power stations and heating installations, include boiler feed pumps (feedwater pumps); condensate, reactor and storage pumps (often suitable for use in both pump mode and turbine mode (PaT)), district heating pumps and circulator pumps.
- Pumps used in the chemical and petrochemical industries include chemical, pipeline, refinery and process pumps (see Back pull-out design), in-line pumps, loading pumps, blending pumps and return pumps.
- The shipbuilding industry employs marine pumps, cargo oil pumps for loading and unloading tankers, ballast pumps, bilge and drainage pumps, dock pumps for filling and draining dock installations, and transverse thrusters.
- Other applications include trench drainage pumps, dredge pumps, fire-fighting pumps, hydrostatic pressure test pumps, scavenging pumps, filling station petrol pumps and vent pumps (see Siphoning line).
- Pump designations naming the fluid handled are also very common.
- Most pumps are used to handle fluids that contain mostly water. These include clean water pumps, drinking water pumps, hot water pumps, cooling water pumps, seawater and brine pumps, condensate pumps, feedwater pumps, waste water and sewage pumps, liquid manure pumps, sludge pumps, pulp pumps, solids-handling
pumps, slurry pumps, cellulose pumps, wood pulp pumps (see Pulp pumping).
- Pumps designated with reference to fluids other than water include oil pumps (heating oil pumps, lubricating oil pumps), fuel pumps, heat transfer pumps, refrigerant pumps, liquefied gas pumps, grease pumps, acid pumps, lye solution pumps, beverage pumps (milk, beer, wine pumps), fish pumps, sugar beet pumps, cossette (sugar beet strips) pumps, fruit pumps and concrete pumps (for the pumping of liquid concrete on building sites)
The designation of pumps according to their drives provides information on the type of drive used: hand pumps, engine-driven pumps, turbine-driven pumps, geared pumps, electric motor-driven pumps, flanged motor pumps, submersible motor pumps, wet rotor motor pumps, canned motor pumps and magnetic drive pumps.
Centrifugal pump designations based on their material primarily relate to the casing material. The various individual components of a pump are made of the material best suited for their particular purpose, which is not necessarily the same for all components (see Material selection). In addition, only the material groups are named in this classification:
Pump designation based on casing material
- Concrete casing pump
- Bronze pump
- High-grade steel pump (i.e. stainless steel pumps)
- Cast iron pump
- Ceramic pump (stoneware and porcelain pumps)
- Plastic pump
- Nodular cast iron pump
- Cast steel pump
In many cases, the wetted parts of a centrifugal pump are protected with a lining or coating (protective layer), e.g. hard-faced pumps, enamelled pumps, and plastic- or rubber-lined pumps (see Slurry pump). This renders terms like "corrosion-resistant" or "wear-resistant" inadequate as a means of pump classification; the complex interrelationship between pump material, fluid handled, flow velocity and temperature means that these terms cannot convey more than a rough concept unless more detailed information is included.