Intro4u2u

Once considered the theoretical concept of academics, rarely applied in practice, life cycle cost analysis is fast becoming the accepted method for the evaluation of both capital projects and items of replacement plant. Indeed to assist pump users in the evaluation of whole life costs, the Confederation of Pump Manufacturers has in 1999 issued a specification (LLC) for establishing and reducing Life-cycle costs.
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The developed world has become acutely aware of the effect of its waste and the introduction of levies on CO2 emissions, now directly taxes the inefficient users of energy. Globalisation is squeezing maintenance budgets and demanding an increased mean time between major service outages.
Initial capital cost is, in most instances, a fraction of the whole life cost of a typical pumping installation. Energy consumption, unplanned downtime, maintenance and replacement parts can easily equate to in excess of 95% of the total life-cycle cost.
The increasing recognition amongst pump users that post installation costs clearly outweigh capital costs and are therefore the only true economic indicator applicable to capital purchases, prompted SPP Pumps Ltd to set up a combined Marketing & Engineering team to develop a range of low life-cycle cost utilities pumps.

Life-cycle Cost Analysis
What are the real costs associated with procuring, operating and maintaining water utility pumping plant? What are the largest, most variable or most invisible costs? Life-cycle cost can be broken-down for analysis purposes into a number of key components.
§ Initial Capital Cost
§ Operating/Energy Costs
§ Replacement/Wear Part Costs
§ Maintenance & Repair Costs
§ Disposal Costs

Initial Capital Cost
Capital cost is the most visible cost and has historically been the primary selection criterion for most items of capital equipment. Pump users are now becoming increasingly aware of post installation costs and their impact on the total cost of ownership. Lowest capital cost purchases rarely prove economic in the longer term and given that the initial capital cost of a centrifugal pump, inclusive of installation, typically equates to between 5%-20% of whole life cost, placing more emphasis on post installation cost will clearly prove much more economic.

Operating/Energy Costs
Energy costs can easily equate to as much as 90% of the whole life cost of a pumping installation, dependant on installed power and equipment utilisation. Analysis of operating costs, in terms of energy consumption, is relatively straightforward, given that pump utilisation and demand profiles are understood and predictable. The wire to water efficiency of existing or proposed installations can be compared and the results projected over the estimated lifetime of the installation. This should be a fundamental component of any tender assessment process or existing asset review procedure. The attached chart clearly depicts the cost of inefficiency, whilst providing visibility into the post installation savings associated with installing the most efficient equipment for a given duty.
Less visible however, is an installations capacity to operate at or near optimum efficiency throughout its operational life. A degree of degradation in hydraulic performance is inevitable with time. This degradation in performance is primarily a result of wear and erosion of internal clearances. Wear rings limit fluid re-circulation between the high and low-pressure areas within a centrifugal pump. A combination of erosion from high velocity fluid passing between the wear ring surfaces and mechanical wear, resultant from shaft deflection widens the clearances allowing an increase in internal re-circulation. Significantly, highlighting the importance of optimum pump selection, this process will be accelerated if the pump operates at a duty point less than 70% or more than 115% of best efficiency flow. The resultant loss of performances usually leads to the pump running for longer periods to deliver a given quantity of fluid. Erosion of hydraulic profiles and increases in the relative roughness of surfaces in contact with the pumped fluid, will also significantly impact on pump performance.

Replacement/Wear Part Costs
The replacement of major components within a pump, whether as a result of wear, erosion or following a component failure is often a very significant contributor to whole life costs. A replacement rotating assembly will typically equate to 70% of the costs of a replacement pump. It is not uncommon for all components forming the rotating assembly to require replacement within the lifetime of a installation. The selection of a conservatively engineered pump, manufactured from high-grade materials should negate this, substantially reducing maintenance costs and increasing the mean time between failure and major service outages.

Maintenance & Repair Costs
The cost of regular monitoring and preventative maintenance is a necessary component of an installations whole life cost and historical evidence shows that regular maintenance is a lower cost option than unplanned emergency repairs. When calculating the cost of maintenance, installation downtime and resultant loss of productivity should be considered. Savings associated with increased mean time between failure and service outages will offset any higher initial capital costs incurred when installing a well-engineered pump, designed for ease of maintenance.
A well-engineered installation should be so designed as to offer good bearing and seal life and facilitate all but a major overhaul insitu, without recourse to disturb either pipework or prime movers.

Features
Having identified the key constituent parts of whole life cost, what key features would be required of a low life-cycle cost centrifugal pump? The majority of pumps employed on utility type applications fall into the category of either, Horizontal Split Casing, Vertical Suspended Bowl or End Suction Pumps. Only the latter are regularly manufactured to recognised international standards e.g. ISO 5199. The requirement for low life-cycle cost pumps was identified as being mainly for branch sizes 150mm and above and not really applicable to the majority of End Suction Pump applications. The following key areas were identified following discussions between pump users and designers.

Mechanical Design
A significant change has taken place over the last decade in that the switch from soft packed glands to mechanical seals for shaft sealing on utility applications is near universal. The benefits of this change however have not been fully realised, as mechanical seal life is generally proportional to certain key aspects of pump performance, not least shaft deflection, vibration levels and seal chamber design. The vast majority of utility pumps available today have their design roots in the packed gland era. In many instances this is leading to premature bearing and seal failures, as many pump shafts are quite simply too flexible without the support of numerous packing rings and neck bushes.
This is arguably the most significant factor, influencing the mean time between failures of utility pumps. Mechanical seals and bearings are intolerant of shaft deflection and residual unbalance. Therefore I suggest that a pump designed for low life-cycle cost would have a shorter span between bearings and an increased shaft diameter when compared to a similar pump designed in the packed gland era. Specifically shafts should be so designed, as to limit shaft deflection at the limits of the operating range of say, 50% - 115% of best efficiency flow, to a maximum of 0.05mm at the seal faces. Bearings likewise should be designed to provide a minimum L10 life of 50,000 hours at these limits.

Hydraulic Design
With the aid of 3-Dimensional Computational Fluid Dynamics, pump manufacturers are now able to produce hydraulic designs that achieve the theoretical maximum efficiency for a given specific speed or impeller geometry. The challenge is then to consistently replicate these designs in material form. High quality manufacturing techniques and procedures are therefore essential, particularly as pump casings and impellers (the most dimensionally critical components of any centrifugal pump) tend to be produced as castings. Only foundry techniques that ensure a high standard of dimensional accuracy and surface finish should be employed in low life-cycle cost pump production.

Efficiency Degradation
The maximum benefit of installing an energy efficient machine will only be realised if performance levels can be maintained for long periods of time between overhauls. Performance degradation is inevitable, however a combination of good hydraulic and mechanical design can have a positive impact in this area and prolong optimum efficiency for much longer periods of time.
Important hydraulic designs consi-derations are:
§ Maintenance of optimum clearances between the impeller outside diameter and the volute cut-water, which will avoid vane pass cavitation.
§ Optimisation of impeller geometry with satisfactory suction specific speed values, this will limit internal re-circulation and facilitate a wide band of operation (30%-115% of best efficiency flow).
§ Apply internal hydrophobic coating (low electronic affinity) in order to reduce the relative surface roughness value of the pump casing; Thus maintaining the relative surface roughness values at a more constant level, unlike that of a bare metal casing, which will oxidise once put into service immediately impacting on hydraulic performance.
Mechanical design considerations:
§ Minimisation of shaft deflection will ensure no contact between impeller eye ring and sealing/wear rings surfaces, thus maintaining as new clearances for longer periods.
§ Often overlooked but highly important is wear ring design. A labyrinth profile will help to provide a staged pressure drop across the wear ring, rather than simply allowing high velocity fluid to flow across wear ring faces rapidly eroding internal clearances.
§ High-grade materials of construction for the pump impeller with good erosion/corrosion properties will ensure that the relative roughness of hydraulic surfaces remain reasonably smooth throughout.

Packaging the Pumpset
When packaging a low life-cycle cost pump with a suitable prime mover, it is important to ensure that the same fundamental design principles be applied to the prime mover, baseplate/mounting assembly.
The benefits of a superior hydraulic design and first class component quality can easily be forfeited by coupling the highly efficient pump to a lower efficiency driver. Likewise bearing and seal design lives will not be realised if the pump and driver are connected via a flexible and inadequate baseplate or mounting frame.
The mounting arrangement as well as being rigid should facilitate a high degree of insitu maintenance. Mechanical seals and bearings should be accessible without recourse to disturb either driver alignment of connecting pipework. This dictates the use of spacer type couplings, if drive end bearings and seals are to be maintainable insitu.

Conclusion/Design Brief
Following the marketing & design review it was decided to develop a range of low life-cycle pumps, for water utility applications, based on the following brief:
A low life-cycle cost centrifugal pump will have hydraulic efficiency close to the theoretical maximum, thus minimising energy costs, identified as the largest single component cost.
In order to meet the demands of the 21st century utility application the pump should show stable characteristics associated with optimum suction specific speed, thus being able to operate reliably and efficiently across a wide range of flow conditions.
Shaft deflection should be kept to the absolute minimum in order to reduce vibration and maximise bearing and seal life. Specifically shaft deflection at the seal face with mechanically sealed pumps should not exceed seal manufacturers recommendations. This calculation should be carried out across all potential operating conditions. The pumps should firstly be designed for mechanical seals, which should be fitted directly onto the pump shaft, facilitating larger shaft diameters and reduced bearing spans..
Pumps should be so designed and pumpsets so configured that mechanical seals and bearings can be removed and replaced insitu without recourse to disturb either pipework or driver alignment. This will substantially reduce maintenance costs.
High-grade materials of construction should be utilised to maximise component life.
Pumps must not only be energy efficient as new, but must maintain a high efficiency for longer period between major overhauls.

SPP’s Lowest Life-cycle Cost Series
During October 2004 SPP Pumps Ltd successfully launched their Lowest Life-cycle Cost Series pumps. The range incorporates all of the key features identified by our business partners and design engineers.

Hydraulic Design
The above test curve depicts the hydraulic performance of a 200 mm discharge Horizontal Split Casing, radial vane impeller, from the Lowest Life-cycle Cost Series range. Values of NS 1,191 and NSS 7,886, in imperial units. Note that high efficiency is achieved from 50% of best efficiency flow, peaking at 90% actual efficiency.

Mechanical Design
Vertical Direct Mounted Low Life Cost Axial Split casing Pump
The above section drawing depicts a packaged axial split casing pump. Firstly note the maintenance features of the pump; the motor mounting stool is extended to accommodate a spacer type coupling, sized to facilitate removal of the drive end seal and cartridge mounted mechanical seal insitu, also note that a product lubricated bearing is fitted at the none drive end. An antifriction bearing would be susceptible should the installation flood or the lower seal fail. A double row thrust bearing assembly is chosen for the drive end.
The short bearing span and generous shaft diameter are clearly evident. In order to replicate good hydraulic design in material form, world class manufacturing methodology is required. Note the internal surface finish on the above double suction impeller. SPP Low Life-cycle cost pumps achieve predicated performance levels with very little variation or need to hand finish components. Austenitic stainless steel is the optimum impeller material combining excellent corrosion and mechanical properties with good castability.
Standard materials of construction for low life-cycle cost utility pumps are:-
§ Casing- Cast Iron (option coated)
§ Impeller – Austenitic Stainless Steel
§ Shaft – Chrome Steel
§ Wear Rings – Grade SG Iron

Baseplates
Low levels of vibration and accurate alignment of pump and driver cannot be maintained without a substantial baseplate. A low life-cycle cost baseplate should be rigid, easily grouted in and incorporate motor alignment screws and machined mounting pads to assist with site alignment.

Vertical Suspended Bowl Pumps
Major savings in civil engineering costs can be achieved by suspending a vertical shaft driven or submersible pump directly into a wet sump, as opposed to constructing a wet sump with accompanying flood resistant dry well.
This has resulted in a growth in vertical turbine and submersible pump sales. The majority of these pumps supplied for utilities applications however are not maintainable in-situ and are proving very expensive to repair. Submersible pumps are prone to electrical failure, owing to ingress of water and tend to have limited bearing life. Motor efficiencies also tend to be low when compared to TEFC energy efficient machines.
The majority of vertical suspended bowl pumps require removal from site into a workshop environment for minor service/replacement of bearings and mechanical seals. Major overhaul can often result in a need to replace line shafting and connecting coupling which are screwed together.
When applying the same low life-cycle cost philosophy to suspended bowl pumps, major consideration was given to mechanical seal replacement in-situ and as such a bespoke spacer coupling was developed, capable of transmitting the total thrust generated by the bowl assemblies, through to the headpiece thrust bearing. This facilitates mechanical seal replacement in-situ, without recourse to disturb either the drive motor or thrust bearing assembly.
It was decided to connect all intermediate shafting by keyed couplings thus facilitating disassembly without risk of damaging these expensive component parts.
Shaft lengths were limited and diameters set to ensure all pumps operate well below the first critical speed. An important consideration given the growing use of variable speed drives.

Summary
This short paper serves to demonstrate the concept employed by SPP in the development of a genuine range of low life-cycle cost pumps.
A thorough understanding of the intended application, operation and maintenance of pumping plant is a fundamental requirement when considering such a project. This could not have been achieved without the input of pump users and designers alike. <<

The Pneutronics Division of Parker Hannifin
announces the release of its new Low Energy Solenoid Valve, the TenX® Le. This
electro-magnetic poppet valve offers high performance in a lightweight 10mm design.

Providing up to 22lpm of flow through a 0.060in orifice, this 2/3-way
normally closed, normally open or 3-way distributor valve operates at up to 30psi with a fast response time (to 5 msec full cycle) and high reliability (rated for 20 million cycles without any performance degradation). The TenX® Le incorporates efficient pulse width modulation (PWM) circuit technology, which consumes an insignificant amount of power and generates minimal heat, making it an ideal fit for portable medical and analytical devices.

“We designed the TenX® Le to meet the needs of customers who require solenoid control and are sensitive to the size and power constraints on their systems.” says Dan Bantz, Product Manager at Pneutronics. “This integrated valve and electronics solution offers a pulse and hold circuit which drastically reduces energy requirements and fits this into a compact 10mm package - essential requirements for portable equipment”

The miniaturized pulse and hold circuit is virtually invisible since it is
perfectly integrated into the 10mm valve package. The circuit function is also
transparent to the application and does not require extra connectivity. The TenX® Le can be used as a stand alone valve with tube connections or in multi-station manifold mount applications.

More information is available at www.parker.com/pneutronics/tenX.

About Parker

With annual sales exceeding $12 billion, Parker Hannifin is the world’s
leading diversified manufacturer of motion and control technologies and systems,
providing precision-engineered solutions for a wide variety of commercial, mobile,
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countries around the world. Parker has increased its annual dividends paid to shareholders for 52 consecutive years, among the top five longest-running dividend-increase records in the S&P 500 index.

Rotary vane vacuum pumps move fluid through the pump using a rotating assembly in the pumping chamber. Typically there are two or more rotating vanes that move the gas or fluid from inlet to outlet. Rotary vane vacuum pumps are positive displacement pumps. The volume of fluid that is transferred by rotary vane pumps depends upon the size of the housing and the area between each adjacent vane. Larger pumps may have additional impeller vanes. As the rotor turns, the ends of the vane barely touch the housing creating a seal from inlet to outlet. The inlet and outlet are often perpendicular, however for vacuum service applications two inlets may be used, one for air supply and the other for the pumped media. The fluid is pressurized as the volume between the vanes lessens during one half-cycle and is suctioned through an intake port during the other half-cycle.

The movement of the media through the pump can be broken down into three phases in rotary vane pumps: 1) Air or fluid moves through the inlet also known as open to inlet (OTI). 2) The vane rotates clockwise or counterclockwise and seals the media between the vanes and the housing wall also known as closed to inlet and outlet (CTIO). With fluids, this volume should remain constant throughout the cycling process. Gases and/or air may be compressed in this phase causing the pressure to increase before the next phase. 3) The media is moved through to the outlet. This is also referred to as the open to outlet (OTO) volume. The rotor blades are positioned to contain a specific volume of air or fluid. The cyclical movement of the vane creates a smooth flow as the fluid is transferred through the pumping chamber. Generally, materials can be chosen for the vane. For example, carbon vanes can be used with inert gases and a variety of other media types. The vane can be internal or external, rigid or flexible.

The manufacturer for rotary vane vacuum pumps can often give the displacement of the pump. The surface dimensions of the housing and rotary assembly may be considered when calculating flow rate. In some rotary vane pumps, as the flow rate increases, the pressure in the pump chamber increases. Various requirements may be needed including vacuum service or air compression. As with most rotary pumps, the viscosity of the media will affect the speed of the drive chosen. The flow rate is also proportional to the motor speed. Magnetic drive, belt drive or direct drive can be chosen for powering rotary vane pumps.

Rotary vane vacuum pumps can be used in a number of applications providing a pressure or vacuum source for laboratory applications and as well as other automation applications. Smaller sizes may have a maximum flow of 3 LPM with pressures ranging from 80-120mbar.move fluid through the pump using a rotating assembly in the pumping chamber. Typically there are two or more rotating vanes that move the gas or fluid from inlet to outlet. Rotary vane vacuum pumps are positive displacement pumps. The volume of fluid that is transferred by rotary vane pumps depends upon the size of the housing and the area between each adjacent vane. Larger pumps may have additional impeller vanes. As the rotor turns, the ends of the vane barely touch the housing creating a seal from inlet to outlet. The inlet and outlet are often perpendicular, however for vacuum service applications two inlets may be used, one for air supply and the other for the pumped media. The fluid is pressurized as the volume between the vanes lessens during one half-cycle and is suctioned through an intake port during the other half-cycle.

The movement of the media through the pump can be broken down into three phases in rotary vane pumps: 1) Air or fluid moves through the inlet also known as open to inlet (OTI). 2) The vane rotates clockwise or counterclockwise and seals the media between the vanes and the housing wall also known as closed to inlet and outlet (CTIO). With fluids, this volume should remain constant throughout the cycling process. Gases and/or air may be compressed in this phase causing the pressure to increase before the next phase. 3) The media is moved through to the outlet. This is also referred to as the open to outlet (OTO) volume. The rotor blades are positioned to contain a specific volume of air or fluid. The cyclical movement of the vane creates a smooth flow as the fluid is transferred through the pumping chamber. Generally, materials can be chosen for the vane. For example, carbon vanes can be used with inert gases and a variety of other media types. The vane can be internal or external, rigid or flexible.

The manufacturer for rotary vane vacuum pumps can often give the displacement of the pump. The surface dimensions of the housing and rotary assembly may be considered when calculating flow rate. In some rotary vane pumps, as the flow rate increases, the pressure in the pump chamber increases. Various requirements may be needed including vacuum service or air compression. As with most rotary pumps, the viscosity of the media will affect the speed of the drive chosen. The flow rate is also proportional to the motor speed. Magnetic drive, belt drive or direct drive can be chosen for powering rotary vane pumps.

Rotary vane vacuum pumps can be used in a number of applications providing a pressure or vacuum source for laboratory applications and as well as other automation applications. Smaller sizes may have a maximum flow of 3 LPM with pressures ranging from 80-120mbar.

Industrial liquid handling pumps are classified in many different ways. They are distinguished by materials of construction, media pumped, industries or applications served, pressure and flow levels, and physical orientation. For this product area, however, industrial liquid handling pumps are distinguished by the media pumped and the fluid motive mechanism, which can be separated into two broad categories of pumping action: dynamic and displacement.

Dynamic or kinetic industrial liquid handling pumps operate by imparting energy into the fluid, frequently by increasing its velocity to a level greater than that allowed by the fluid outlet port. This energy is thereby converted to higher pressure. Displacement pumps compress fluid mechanically by decreasing the volume of a chamber that contains the fluid. Many configurations of piston-cylinder combinations, diaphragm oscillation, and rotating members are used to achieve this compression. While many ranges of flow and pressure capabilities are available for all industrial liquid handling pumps, dynamic pumps are characterized by the ability to produce high flow rates.

Displacement industrial liquid handling pumps are distinguished by their comparatively high-pressure capabilities. Specific pump types include axial, bladder, cantilever, centrifugal, circumferential piston, diaphragm, double diaphragm, dosing or metering, drum, gear, hand, jet, linear, lobed rotor, manual, peristaltic, piston or plunger, radial piston, rocking piston, rotary vane, regenerative blower, screw, scroll, syringe, and turbine. Other types of displacement industrial liquid handling pumps may also be available.

Industrial liquid handling pumps are designed to work with specific fluids and/or applications. Some pumps may be suitable for multiple applications. Common fluids and applications for industrial liquid handling pumps include general-purpose fluid transfer, chemicals, cryogenic materials, food processing, fuel or oil, high temperature fluids, high viscosity fluids, hydraulic fluid, medical or surgical fluids, refrigerants, sludge or sewage, slurry, solids or gravel, thermoplastics, and water.

Specifications to consider when selecting industrial liquid handling pumps include maximum flow rate, maximum pressure, maximum temperature, and maximum power drive. Flow capacity must be specified separately for air or gas and liquid pumps. Maximum pressure refers to the maximum level of air pressure generated at the pump outlet. Typically, units are referenced to one atmosphere, as in psig or psi gauge. Maximum flow may not occur at maximum pressure. Depending on the pump style, maximum temperature can refer to either maximum fluid temperature being pumped, or the upper limit of ambient conditions. Maximum drive power is the rated power of the motor or engine which drives the industrial liquid handling pumps.

Cryogenic pumps are designed to move coolants and cryogenic liquids. They are built to withstand and operate in extremely cold temperatures. Cryogenic pumps feature hermetically sealed designs to minimize heat leakage from the motor or contamination by process fluids into the cryogenic fluid.

Long shaft cryogenic pumps are designed with the pump motor and mounting flange separated from the pump impeller by a long shaft. The pump impeller is submerged in the cryogen or freezing liquid. This minimizes the leaking of heat from the motor into the frozen or freezing cryogenic fluid. Long shaft cryogenic pumps may be welded or bolted to a variety of cryogenic equipment, including dewars and cryostats. A dewar is a specially insulated container designed to store liquefied gases, such as the liquid nitrogen used as a coolant in cryogenic applications. A cryostat is a device used to maintain the temperature of the coolant. A centrifugal pump is typically used to transfer cryogenic liquids between a storage tank or tanker car because of their ability to produce and maintain a high flow rate.

Cryogenic pumps may also be submersible. A submersible cryogenic pump is frequently used in applications where heat leak is not the most important factor. Submersible cryogenic pumps are used as pumps in vehicles that use liquefied natural gas or in the liquid hydrogen propellant system in a rocket. Cryogenic pumps for use in extremely cold environments are usually constructed with a vacuum housing to provide a barrier between the motor and the cryogenic fluid. Cryogenic pumps are used to circulate coolant in a variety of applications, including cooling high temperature superconducting cables or magnets, for cooling synchrotron beamline crystals, and as pumps in prototype slush hydrogen applications.

Specialty vacuum pumps are specialty or proprietary products and accessories related to vacuum pumps. Specialty vacuum pumps include portable, handheld, and miniature vacuum pumps; low power or 12-volt vacuum pumps, and a variety of other devices. Specialty vacuum pumps also include low power electric pumps for use in vehicles. A 12 volt vacuum pump is commonly used to create the vacuum necessary for operating power brakes. This type of electric vacuum pump is also used in other portable or battery-powered devices.

Specialty vacuum pumps are used for many different industrial and scientific applications, including purification of chambers in chemical or semiconductor manufacturing, degassing fume areas in laboratories, and for holding components in place during machining processes. A specialty vacuum pump used for handheld applications may include devices for bleeding brake lines on cars and trucks. A hand vacuum pump often employs a trigger-style design, allowing an operator to easily disengage the vacuum. Other specialty vacuum pumps include miniature or even microscopic pumps for use in small apparatus or motors. A mini vacuum pump may be battery-powered and used in robotic applications or in applications where space is limited.

Specialty vacuum pumps for other types of applications include rotary vane vacuum pumps and liquid ring vacuum pumps. A rotary vane vacuum pump consists of a hollow body with a rotating cylinder that is mounted off-axis with two opposing vanes. The motion of the turning rotor causes the volume present between the two vanes and the hollow body of the pump to vary at each half turn. Rotary vane vacuum pumps are used in all kinds of vacuum applications, including thin film deposition and other semiconductor processes. A liquid ring vacuum pump consist of a rotating impeller with multiple blades mounted in a pump housing. As the impeller rotates, centrifugal force moves a liquid against the outside wall, forming a seal. Liquid ring vacuum pumps work like a piston, compressing the gas in the chamber as the impeller moves toward the top of the pump housing

Centrifugal pumps consist of a set of rotating vanes, enclosed within a housing or casing, used to impart energy to a fluid through centrifugal force. The pump has two main parts: a rotating element which includes an impeller and a shaft, and a stationary element made up of a casing (volute or solid), stuffing box, and bearings. Centrifugal pumps operate using kinetic energy to move fluid utilizing an impeller and a circular pump casing. The impeller produces liquid velocity and the casing forces the liquid to discharge from the pump converting velocity to pressure. This is accomplished by offsetting the impeller in the casing, and by maintaining a close clearance between the impeller and the casing at the cutwater. The fluid enters the pump near the center of the impeller and is moved to its outside diameter by the rotating motion of the impeller. The vanes on the impeller progressively widen from the center of the impeller that reduces speed and increases pressure. This allows centrifugal pumps to produce continuous flows at high pressure. By forcing the fluid through without cupping it, centrifugal pumps can achieve a very high flow rate.

Centrifugal pumps are used in many industries. Some of their most common applications /media transferred include: general purpose fluids, pure water, sludge and sewage, slurry, high viscosity fluids, power generation, the paper industry, the petroleum industry, chemicals and corrosives, gravel and solid materials, high temperature materials, and marine applications.

Centrifugal pumps generate flow by using one of three actions: radial flow, mixed flow, and axial flow. These classifications do not rate the performance quality of the pump, they are merely groupings based upon the pump’s action.

Radial flow pumps are centrifugal pumps in which the pressure is developed wholly by centrifugal force. In mixed flow pumps, the pressure is developed partly by centrifugal force and partly by the lift of the vanes of the impeller on the liquid. Axial flow centrifugal pumps develop pressure by the propelling or lifting action of the vanes of the impeller on the liquid.

The overwhelming majority of contractor pumps use centrifugal force to move water. Centrifugal force is defined as the action that causes something, in this case water, to move away from its center of rotation.

All centrifugal pumps use an impeller and volute to create the partial vacuum and discharge pressure necessary to move water through the casing. The impeller and volute form the heart of the pump and help determine its flow, pressure and solid handling capability.

An impeller is a rotating disk with a set of vanes coupled to the engine/motor shaft that produces centrifugal force within the pump casing. A volute is the stationary housing (in which the impeller rotates) that collects, discharges and recirculates water entering the pump. A diffuser is used on high pressure pumps and is similar to a volute but more compact in design. Many types of material can be used in their manufactire but cast iron is most commonly used for construction applications.

In order for a centrifugal pump, or self priming, pump to attain its initial prime the casing must first be manually primed or filled with water. Afterwards, unless it is run dry or drained, a sufficient amount of water should remain in the pump to ensure quick priming the next time it is needed.

centrifual pumps - how do they work

As the impeller churns the water (see figure above), it purges air from the casing creating an area of low pressure, or partial vacuum, at the eye (center) of the impeller. The weight of the atmosphere on the external body of water pushes water rapidly through the hose and pump casing toward the eye of the impeller.

Centrifugal force created by the rotating impeller pushes water away from the eye, where pressure is lowest, to the vane tips where the pressure is highest. The velocity of the rotating vanes pressurizes the water forced through the volute and discharges it from the pump.
Water passing through the pump brings with it solids and other abrasive material that will gradually wear down the impeller or volute. This wear can increase the distance between the impeller and the volute resulting in decreased flows, decreased heads and longer priming times. Periodic inspection and maintenance is necessary to keep pumps running like new.

Another key component of the pump is its mechanical seal. This spring loaded component consists of two faces, one stationary and another rotating, and is located on the engine shaft between the impeller and the rear casing (see figure below). It is designed to prevent water from seeping into and damaging the engine. Pumps designed for work in harsh environments require a seal that is more abrasion resistant than pumps designed for regular household use.

centrifugal pumps impeller and a volute assembly

Typically seals are cooled by water as it passes through the pump. If the pump is dry or has insufficient water for priming it could damage the mechanical seal. Oil-lubricated an occasionally grease-lubricated seals are available on some pumps that provide positive lubrication in the event that the pump is run without water. The seal is a common wear part that should be periodically inspected.

Regardless of whether the application calls for a standard, high pressure, or trash every centrifugal pump lifts and discharges water in the same way. The following section will point out design differences between these pumps.

Standard Centrifugal Pumps
Standard centrifugal pumps provide an economical choice for general purpose dewatering. A number of different sizes are available but the most common model offerings are in the 2 to 4 inch range with flows from 142 to 500 gallons per minute (GPM) and heads in the range of 90 to 115 feet.

these pumps should only be used in clear water applications (agricultural, industrial, residential) as they have a limited solid handling capability of only 10% by volume. The impellers typically use a three-vane design (see figure below) and the volute is compact, preventing the passage of large solids. The rule of thumb is the pump will only pass spherical solids 1/4 the diameter of the suction inlet.

centrifugal pumps - impeller and volute what do they look like

One advantage these pumps have over comparably sized trash models is their low initial cost. There are several reasons for this difference. Lower horsepower engines are utilized that are smaller in size and more fuel efficient. The mechanical seals, since they are not subjected to harsh working conditions, can be made of less costly material. Additionally, the casings are smaller and have fewer machined parts that when combined with the smaller engines make the pumps much lighter in weight.

High Pressure Centrifugal Pumps
High pressure centrifugal pumps are designed for use in applications requireing high discharge pressures and flows. Contractors may use them to wash down equipment on the job site as well as install them on water trailers. Other uses include irrigation and as emergency standby pumps in areas where there is a high risk of fire.

Typically these pumps will discharge around 100 GPM and produce heads in excess of 240 feet. The pump may have a 2 inch suction port and up to three discharge ports of varying size for added versatility. The impellers used on these pumps are a closed design (see figure below) and not open like those used on other types of centrifugal pumps. Similarly the diffuser is more compact than a regular volute in order to generate the high discharge pressures.

high pressure centrifugal pumps - impeller and volute what do they look like

These pumps by design are not capable of handling any types of solids or even sandy water, Silt, sand or debris would almost immediately clog the pump if allowed to enter into the casing. Additionally, the impeller and diffuser may be made of aluminum rather than weather resistant cast iron since they are not subject to abrasive materials. It is recommended that a mesh net always be placed over the suction strainer if the pump is being used in dirty water.

Trash Centrifugal Pumps
Trash centrifugal pumps get their name from their ability to handle large amounts of debris and are the preferred choice of contractors and the rental industry. The most common sizes are in the 2 to 6 inch range producing flows from 200 to 1,600 GPM and heads up to 150 feet.

The rule of thumb is that a trash pump will generally handle spherical solids up to 1/2 the diameter of the suction inlet. Solids (sticks, stones and debris) flow through without cloggin making themideal for the water conditions typically found on job sites. Trash pumps handle up to 25% suspended solids by volume.

Trash pumps offer another benefit in that they can be quickly and easily disassembled for service or inspection. While standard pumps require special tools that are not always available the inside of a trash pump gousing can usually be accessed with common tools.

Customers occasionally ask why a trash pump costs more than standard centrifugal pumps. One big reason is that higher horsepower engines are neeed for trash pumps. The impeller is typically a cast iron two-vane design (see figure below) and a large volute is required to handle the higher volume of water and debris. The mechanical seal - like the impeller and volute - is selected for its abrasion resistance and more parts are machined for the casing. While there is a higher initial cost it must be noted that is is recovered through the reduced maintenance over the life of an often used pump.

Centrifugal pumps
Centrifugal pumps are used in the transfer of cryogenic liquid between storage tanks or road tankers. These pumps have the ability to produce a high flow rate and present a low maintenance requirement. Fully truck mounted systems are also available.

As a standard Cryostar equipes the whole range with its famous composite mechanical seal providing an extended lifetime that is 3 to 4 times longer than the carbon rings commonly used.

Our range:
Gearbox driven
CBS : Stationary or truck mounted pump for liquid transfer, with a flow capacity of 200 GPM for a design pressure of 725 PSI
GBS : Stationary or truck mounted pump for liquid transfer, with a flow capacity of 160 GPM for a design pressure of 580 PSI
Direct coupled
GBSD : Stationary or truck mounted pump for liquid transfer with Frequency Converter, for a design pressure of 725 PSI
VS : Submerged pump designed for low temperature applications like LCO2 or LNG transfer, with a flow capacity of 210 GPM for a design pressure of 360 PSI
CO : Stationary or truck mounted pump for liquid transfer with Frequency Converter, with a flow capacity of 35 GPM for a design pressure of 525 PSI
Hydraulic driven
CSH : hydraulic driven pump capable of high performance unloading with flows up to 240 GPM for a design pressure of 435 PSI.
Complete systems for Semi Trailers
Mixtran : Self contained centrifugal pump system for road tankers powered through a generator coupled with truck engine
Hytran : Self contained centrifugal pump system for road tankers coupled with hydraulic motor powered through a complete oil system.

Centrifugal Pump
Grainger Centrifugal Pump

Grainger, an industrial supply leader offers a wide range of industrial supplies including many centrifugal pump offerings. Whether you are looking for a multi-stage booster centrifugal pump or a portable self-priming centrifugal pump, Grainger has the centrifugal pump that will fit your specific needs. If you would like to learn more about the many different centrifugal pumps Grainger offers, please take the time to visit out homepage.
Centrifugal Pump Information

A centrifugal pump is classified into one of three basic categories The three centrifugal pump categories are radial flow, mixed flow, and axial flow. A radial flow centrifugal pump is a centrifugal pump in which the pressure is developed entirely by centrifugal force. A mixed flow centrifugal pump is a centrifugal pump in which the pressure is developed partly by centrifugal force and partly by the lift of the impeller on the liquid. The third type of centrifugal pump is the axial flow centrifugal pump. The axial flow pump is a centrifugal pump in which the pressure is developed by the propelling or lifting action of the vanes of the impeller on the liquid. The two main components of a centrifugal pump are the impeller and the volute. The impeller produces liquid velocity and the volute forces the liquid to discharge from the pump converting velocity to pressure.
Centrifugal Pump Offerings

At Grainger we are sure to have a centrifugal pump that will meet your needs. From a magnetic drive centrifugal pump to a multi-stage booster centrifugal pump and everything in-between, Grainger is equipped to meet all of your centrifugal pump needs. If you are interested in learning more about the centrifugal pump offerings from Grainger, please take the time to visit our homepage and browse through our entire online catalog.
More Information: Centrifugal Pump

Grainger is the place to find the centrifugal pump you are looking for. In addition to our centrifugal pump offerings, we also have a large selection of other industrial supplies. From hand tools and safety equipment to respirators and two way radios