vfd hydraulic pump pricelist

A hydraulic power unit (HPU) is a common product that IFP supplies to its customers for all types of hydraulic applications.  Most customers order their HPUs with standard electric motors and across-the-line motor starters.  These electric motors spin at a constant RPM.  Because the electric motor spins at a constant RPM, the hydraulic pump coupled to the motor is constantly flowing oil and is likely wasting energy in between system operations.

By allowing the VFD controlled HPU to match the system pressure and flow requirements by varying the pump speed, there are several other advantages to using these VFD controlled HPU systems.  By reducing energy put into the system, less heat is generated that has to be dissipated by the system.  There are typically noise reductions with VFD controlled HPUs.  With reduced heat and reduced system shock, this typically leads to longer component life depending on the load cycle.  Hi-lo systems can now be completed with just one fixed displacement hydraulic pump.  By over-speeding the pump for extra volumes of fluid, the VFD controlled system does not need a low pressure/high flow pump along with the high pressure/low flow pump.  Charging an accumulator can become more efficient as well.  Once the accumulator is charged, the VFD controlled HPU can slow down the flow output of the hydraulic pump and maintain the system.  Unloading the pump for accumulator charging is typically done with extra valves and consuming unnecessary energy.  Overall costs of hydraulic systems can be reduced because smaller hydraulic pumps can be used, less valves are required, less or no cooling for heat dissipation, and smaller reservoirs can be used.

The applications are endless for VFD controlled HPU systems.  These systems can be used on anything from a simple filter and lubrication system to extremely complex test stands and presses.  With increased efficiency and control, VFD controlled HPU systems will become more common in industry.

For more information on how you can utilize Drives and VFD controlled HPUs, please contact us here to receive a personalized contact by an IFP Application Engineer:

VFD, short for Variable Frequency Drive, is an energy saving device for controlling AC motor speed by converting mains power supply AC - DC - AC with variable frequency & voltage output. The VFD adjusts voltage and frequency of the output power supply by the internal IGBT, and supplies the power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. In addition, VFD has many protection functions, such as overcurrent and overvoltage, overload protection and so on.

ATO sells VFD"s power range from 1/2hp to 300hp, include single phase input and output VFDs from 1/2hp to 7.5hp, 110v/120v input VFDs from 1hp to 7.5hp, single phase input to three phase output VFDs from 1/2hp to 10hp, three phase input/output VFDs from 1hp to 300hp. All VFDs are manufacturer direct sale and quality guaranteed. Widely used in fans, pumps, lathes, cable machinery, printing and dyeing equipment, chemical machinery, plastic machinery, etc. The following are ATO variable frequency drive price lists for your reference. If you want more information, please go to ATO VFD products page.

Compared with traditional variable speed drives, the Bear 100 VFD series water pump dedicated variable frequency drive is more efficient and easier to install and operate. In addition,

The Bear 100 VFD variable frequency drive with a 137Amp can be used with any standard AC motor, IP65 protection rating Bear 100 VFD could install on the motor directly, no need for extra PLC, relay, contactors, and control box. The built-in application software makes it the most convenient driver for debugging, programming and operation.

The professional control and protection function for the pump and motor, the soft start and stop, incredibly improve the service life of the pump, motor, and pipe. All these features make this compact and easy-to-use drive reliable and energy-saving up to 70%, suitable for almost any application.

The Bear retrofitting of existing pumping stations means substantial energy savings, mainly when operating under partial loads, can be achieved. It can be efficiently transformed into any standard asynchronous pump motor suitable for variable speed drive operation.

The modular design of Bear makes it fundamentally different from ordinary variable speed pump drives. You can efficiently configure almost any pump arrangement according to your needs. It can up to six pumps be combined.

The cost saving is not only reflected in the energy-saving, which saves the customer’s use cost! The pump operation and monitoring protection logic is built into the Bear’s inverter so that it does not require additional relays or contactors; PLC can realize the function of controlling and protecting the water pump and motor; the operation is simple; no professional electrical engineer is required.

Centrifugal pumps are generally sized to operate at or near the best efficiency point at maximum flow. The maximum flow requirements, however, frequently occur for a very short period during the operating cycle with the result that some method of flow control is required. The traditional method to flow control has used valves, which increase system pressure, inherently waste energy, and generally cause the centrifugal pump to operate at reduced efficiencies.

VFDs (Variable Frequency Drives) can achieve reduced flow by providing variable speed pump operation. This results in reduced system pressure and operation near the pump"s Best Efficiency Point. In addition, maintenance costs might be reduced. This article will discuss the energy savings potential of variable frequency drives followed by a brief description of the operation and relative benefits of VFDs.

Centrifugal pumps are used on many industrial and commercial applications. Many of these pumps are operated at fixed speeds, but could provide energy savings through variable speed operation. Reviewing the affinity laws for centrifugal pumps and a typical operating cycle for a centrifugal application will show this.

Figure 1 shows the physical laws of centrifugal pumping applications. The flow is directly proportional to speed; pressure is proportional to the square of the speed; and power is proportional to the cube of the speed. These relationships can also be expressed numerically as shown in Table 1. Theoretically, it would be possible to operate at 50% flow with only 13% of the power required at 100% flow. Since the power requirements decrease much faster than the reduction in flow, the potential exists for significant energy reduction at reduced flows.

These characteristics are important when one considers a typical duty cycle for a centrifugal pump application. A typical operating cycle might be represented by the bar chart shown in figure 2. Centrifugal pumps are generally sized to handle the peak flow requirements, which typically occur for very short periods of time. Consequently, the equipment would be operated at reduced flows most of the time. For this example, the system would be operated below 70% flow over 94% of the time. Thus, this sort of duty cycle could provide energy savings by variable speed operation of the centrifugal pump.

An understanding of the basic operating characteristics of centrifugal pumps is necessary to apply variable frequency drives to this particular application.

Figure 3 shows a centrifugal pump curve describing the head (or pressure) versus flow characteristics of a typical centrifugal pump. This curve shows that the centrifugal pump will produce limited flow if applied to a piping system in which a large pressure differential is required across the pump to lift the liquid and overcome resistance to flow (as at point A). Higher flow rates can be achieved as the required pressure differential is reduced (as at point B).

To determine where along this curve the centrifugal pump will operate in a given application requires the additional information provided by the system curve. This curve, shown in figure 4, represents the characteristics of the piping system to which the centrifugal pump is applied. The head required at zero flow is called the static head or lift.

This shows how many feet of elevation that the centrifugal pump must lift the fluid regardless of the flow rate. Another way to describe static head is to think of it as the amount of work needed to overcome the effects of gravity.

The intersection of the centrifugal pump and system curves shows the natural operating point for the system without flow control, as shown in figure 5. This intersection would generally be chosen to ensure that the centrifugal pump is operated at or near its best efficiency point.

Figure 6 shows a typical centrifugal pump and efficiency curve for operation at a fixed speed. It can be seen that for fixed speed operation, the efficiency varies as flow is adjusted. For variable speed operation however, the affinity laws predict that the centrifugal pump curve will shift downwards for reduced speed and the efficiency curve will shift to the left in such a way that efficiency will remain constant relative to points on the pump curve for reduced flows.

Historically, fixed speed AC motors have driven centrifugal pumps and reduced flow has been achieved by using control valves as shown in figure 7. Closing the valve reduces the flow by increasing the friction in the system. The modified system curve and the new operating point can be represented as shown in figure 8. Note that the desired reduction in flow has been achieved, but at the expense of increased system pressure relative to 100% flow.

Reducing the centrifugal pump speed causes the pump curve to shift downwards as shown in figure 9. Since the operating point is still determined by the intersection of the reduced speed pump curve and the system curve, it is possible to achieve the same reduced flow as achieved with a valve, but at significantly less pressure.

In addition to energy savings by VFD, which are discussed in detail later, operation at reduced pressures can result in longer pump seal life, reduced impeller wear, and less system vibration and noise. These benefits could provide additional savings over potential energy savings by variable frequency drive.

Therefore, for any given liquid, the power that the centrifugal pump must transmit is proportional to the head times the flow and can be represented by rectangles for each operating point as shown in figure 10.

The valve control rectangle includes both the dark and light shaded areas. Speed control uses only the lighter shaded portion of horsepower. Therefore, the potential energy saving available at this particular flow point is represented by the darker rectangle. This situation results in a substantial reduction in output power required through the use of variable frequency drive control rather than valve control (see differences between VFD and valve control). Relating this reduction in required output power to input power, which is the basis for the user"s power bill, requires consideration of the efficiency of the centrifugal pump and flow control elements.

(2) Slip control refers to fluid and magnetic couplings, often referred to as hydraulic or eddy current couplings. Wound rotor motors are also slip devices.

Thus, the first step toward realizing energy savings on centrifugal pumping applications is the decision to use VFD for pumps. The second step is to use the most efficient VFD that meets the application requirements.

VFD energy losses can vary substantially between VFD types, Solid-state drives have much lower losses than slip devices and closely approximate ideal, 100% efficient operating characteristics as shown in figure 11.

Centrifugal pump efficiencies at various operating points are readily available from the pump manufacturer in the form of an efficiency map superimposed over the centrifugal pump curves for various impeller sizes as shown in figure 12.

The state-of-the-art has progressed dramatically in electronics in recent years. Advances in logic have produced large scale integrated and microprocessor devices that will continue to increase the capability of VFDs. Improvements in thyristors have resulted in decreased size while the development of IGBTs have expanded capabilities and size ranges. VFDs are expected to continue decreasing in cost and increasing in performance in the years to come. Besides longer-term energy savings, the initial cost differential between installing a VFD / motor package as compared to an AC starter/motor package is continually diminishing.

Dramatic increases in energy costs in recent years have made variable speed flow control through the use of VFDs economical in many instances. Large users of centrifugal pumping equipment would be wise to begin gaining experience with these VFDs now.

The most important choice to be made in choosing the VFDs is the decision to select a non-slip, solid-state VFD. Any such VFD can offer dramatic energy savings by efficiently matching the energy consumed to the hydraulic load requirements at any given moment.

In general, if the electrical engineer does not fully understand the operation variables of the pumping operation, he will not be able to design a proper operation and protection gear.I highly ...

Mechanical VFDs include the following subtypes:Variable pitch drive – a belt and pulley drive where the pitch diameter of one or both pulleys is adjustable, giving a multi ratio and hence a ...

There are two ways in tension control, one way is to control the output torque of the motor, the other way is to control the motor speed. Variable frequency drive (VFD) open-loop control mode is ...

In most U.S. states, running a 100-horsepower pump motor continuously for a year can rack up more than $40,000 in energy expenses. Improving efficiency in industrial pumping systems is one way to reduce these costs.

While variable frequency drive (VFD) technology can significantly increase system efficiency by controlling pump speed, not every application requires a VFD. To determine when to apply this technology, end users must conduct detailed calculations to verify the cost-effectiveness of using a VFD.

A VFD varies the speed of a three-phase, alternating current (AC) induction motor by adjusting the voltage and frequency of the motor"s input power (see Image 1). Varying the speed of the motor improves efficiency by changing the pump"s output to match actual pressure/flow requirements.

Any new or existing pump system with dynamic demand is a candidate for a VFD installation. If the pump often operates at a low flow rate, controlling motor speed with a VFD will result in much lower energy costs compared with running the motor at full speed and throttling its flow output with a control valve.

Because required pump motor power increases at a much faster rate than flow, pumping fluid faster than necessary can alter energy use significantly. In addition to reducing power consumption, a VFD can also help reduce mechanical wear, maintenance and related costs.

A VFD"s ability to dramatically increase energy efficiency when used to control a centrifugal pump (see Image 2) is explained by the pump affinity laws.

The pump affinity laws are based on constant impeller diameter and varying speed. The premise of these laws is that, for a given pump with a fixed-diameter impeller, capacity is directly proportional to the speed (Equation 1), head is directly proportional to the square of the speed (Equation 2), and required power is directly proportional to the cube of the speed (Equation 3).

Put simply, if pump speed decreases by 50 percent, then flow decreases to 50 percent, pressure decreases to 25 percent, and power consumption decreases to 12.5 percent. So the potential for energy savings increases as the demand for flow and corresponding pump speed decreases.

To determine if a VFD is an efficient and cost-effective option for either a new or retrofit design, end users must first consider operating conditions and then calculate cost and energy savings by following 11 steps.

To evaluate potential cost savings, determine the operating speed range. Pumping system characteristics are defined by the system curve, which describes flow rate at a specific pressure. To determine the system curve, static and friction head must be known.

In an existing system, the system curve is calculated using data from pressure and flow measurements, control valve position and pump motor electric current measurements. If valves are used to add or remove equipment from the system flow path, then system curves must be created for each configuration. Once that is complete, compare the manufacturer"s pump curve with the operating points on the system curve to determine the correct pump speed for each configuration.

To estimate potential savings from reduced power consumption, determine the amount of time the pump runs at the different operating points on the system curve. Hours spent operating at lower flow rates and head pressures along the system curve offer the greatest opportunities for cost savings. Variations in on-peak versus off-peak cost of electricity should also be considered.

Calculations should include pump efficiency and motor efficiency, as well as VFD losses of about 3 percent. When estimating potential cost savings, compare the operating costs of a fixed-speed pump against those of a variable speed pump for one year.

The installation of a VFD may require additional components. Electromagnetic interference (EMI) filters, line/load reactors and radio frequency (RF) filters may be needed as part of the installation. Because a VFD is typically larger than the motor starter it will replace, a larger electrical enclosure may be needed. When retrofitting a VFD, the cost of new power cables to the inverter and VFD-rated cable to the motor must also be taken into account. Typical installed costs of VFD systems range from $200 to $500 per horsepower (HP).

Suppliers can assist users in selecting a VFD that is properly sized and that includes any necessary filters and reactors. If the application involves an existing three-phase motor, the motor may be used if the winding insulation rating is sufficient. The motor should have an insulation class rating of F or higher.

Compare the savings resulting from reduced power consumption with the cost of the installed VFD to determine if the return on investment is sufficient to justify the expense. Operating the pump and motor at lower speeds may lead to increased service life and reduced maintenance intervals, and these savings should be included in the calculations.

Assume a centrifugal pump operating with a 15-HP, three-phase AC motor has across-the-line starting at 460 volts AC, 60 Hertz. The pump typically turns at a constant speed of 1,750 rpm, consumes 10 HP and discharges 200 gallons per minute (GPM) with a head of 120 feet. A throttling valve is used to vary pump output from 200 to 100 GPM.

A review of the system indicates that the pump normally operates with the throttling valve positioned to limit pump discharge to 100 GPM. The reduced flow rate represents 50 percent of the pump capacity, occurring 90 percent of the time.

Based on the affinity law, pump capacity is directly proportional to pump speed, so a reduction in speed to 50 percent will achieve an identical reduction in capacity/flow rate (see Equation 4).

Table 1 shows that, according to the pump affinity laws, reducing the flow by 50 percent cuts the pump head pressure to 25 percent of rating. A readily available VFD energy savings calculator can help determine the potential cost savings achieved by using a VFD.

In this example, based on 4,160 hours of annual run time and a cost of $0.12 per kWh, annual energy consumption drops from 21 to 8 megawatt-hours when the pump is controlled with a VFD as opposed to the original control method using a throttling valve.

This represents an annual savings of $1,589 or 62.4 percent. With an estimated installed cost of $4,000 \uc0\u8232 for a 15-HP VFD, the payback period is 2.5 years.

As the cost of electricity continues to rise, the need to reduce energy consumption becomes even more important. As demonstrated by the pump affinity laws, operating a pump at lower speeds can significantly reduce energy consumption.

Compared with operating a pump at full speed with a throttling valve, using a VFD to run a pump at the desired lower speed usually is a more efficient option. The VFD reduces energy consumption, eliminates the need for a throttling valve, simplifies piping design and installation, and cuts maintenance costs.

VFD technology was developed in response to the limitations of AC power. AC motors, such as the ones powering industrial pumps, rotate at a rate set by the incoming power and the number of poles inside the motor. Since AC power in the US is supplied at a standard 60 Hz frequency, this means that standard single phase two-pole motors spin 60 times per second.

Adding more sets of poles reduces the speed without any need to alter the incoming electrical frequency. However, you can’t just swap out an electric motor with more or fewer poles every time you need to change the operating speed of a pump. Transistor systems that allow you to turn specific motor poles on and off have been available for decades, but these systems are complex and often lack the fine control needed for industrial pumping. Instead, VFD’s change the frequency of the power supply, allowing for exact and immediate adjustments to the pump operation.

The VFD works by taking in AC power at the 60 Hz frequency, converts it into direct current (DC) power through a rectifier circuit, and sends it through a DC bus to filter the voltage further. Then, power reaches the inverter which creates pulses of DC energy that function like AC current. The pulsing nature of the output mimics AC power enough to create the correct induction processes needed to spin the rotor of the motor. Since DC is easier to control in voltage and frequency, using it instead of true AC power allows the VFD to adjust the electrical supply on the fly. A series of transistors, especially the Insulated Gate, Bipolar Transistor (IGBT), give manual or automatic control over the power output and the resulting EDDY pump performance. Power is easily increased to a sludge pump under heavy load and then dropped again after a blockage passes or the texture of the slurry or sludge being pumped changes.

At NPE2018, both Jomar Corp., Egg Harbor Township, N.J., and Bosch Rexroth Corp., Bethlehem, Pa., introduced new products that provide an educational illustration of the differences between two types of energy-saving variable-speed drives for hydraulic pumps.

The term “servo-hydraulic” has gained currency to describe new generations of plastics machinery that utilize hydraulic pumps but with energy savings and noise reduction closely approaching those obtained with all-electric servo motors and drives. At the same time, popularity has also been growing for aftermarket retrofits of conventional hydraulics with variable-frequency drives (VFDs), another way of saving energy by varying pump speed—even to zero—according to the instantaneous load demand of the system.

Bosch Rexroth introduced at the show its Sytronix DRn 5020 VFD, aimed specifically for converting variable-displacement hydraulic pumps driven by conventional fixed-speed (1800 rpm) motors to quieter, more energy-efficient variable-speed operation. It reportedly saves up to 75% in electrical energy for systems that have long dwell times; and the average noise reduction is 8 to 10 dBa vs. fixed-speed hydraulic drives. This “intelligent” drive senses the motor torque and pump pressure to calculate the pump displacement, or position of the swash plate, to keep it in the most efficient position for the real-time load requirement. This drive is Industry 4.0 compatible, as it adds operating data collection and digital communications to conventional electric motors and hydraulic pumps that normally do not have these capabilities.

Bosch Rexroth notes that VFDs are considerably less expensive than servo drives, but the firm also points out in a white paper that they provide less tight control over motor speed than servos and have lower dynamic performance—ability to respond and control pressure/velocity changes. VFD drives are thus more suited to steady or slowly changing loads. They also have low-speed limitations and are usable only to 400-500 rpm.

Bosch Rexroth points to an instructive use of both its MSK servo motor and the new Sytronix DRn 5020 on Jomar’s new IntelliDrive injection-blow molding machines. Jomar often refers to these machines as “servo-hydraulic,” but the servo drives only the hydraulic pump for the injection unit. The injection and blowing clamps use a pump with the new VFD. The Jomar IntelliDrive 85S at the show boasted 42% lower energy consumption than a standard model 85S and required a 40% smaller oil tank.

Siemens’ Sinamics servopump is built on standard components such as the Sinamics S120 drive platform and distributed I/O, and offers users increased machine output and reduced energy costs by up to 50%.

With any fluid power system, efficiency is always top of the mind, so components and advanced technology that can improve energy consumption are increasingly necessary. To that end, the NFPA last year commissioned a survey to examine the current and potential use of variable speed drives (VSDs) with hydraulic pumps.

Not surprisingly, the overall results showed that respondents believe that the use of VSDs in hydraulic applications will increase over the next three years. They cited VSDs’ high-energy efficiency, improved reliability and low operating cost as key determining factors in the increase of their use. On the opposite end of the spectrum, when asked what discourages the use of VSDs, respondents pointed toward high acquisition or upfront costs, lack of maintenance and after-sales support for VSD technology, and lack of design expertise in their use.

The four main manufacturers of variable speed drives in the U.S. include Eaton, Parker Hannifin, Siemens and Bosch Rexroth. Here, we spoke with representatives from three of those companies—Lyle Meyer, global product manager, Industrial Drives, Eaton Hydraulics; Lou Lambruschi, marketing services and e-business manager, Parker’s Electromechanical and Drives Div.; and Craig Nelson, marketing manager, Drives, Siemens Industry U.S.—to learn how VSDs can change the way hydraulics function in an industrial setting.

Meyer: There are three advantages variable speed drives offer the market— low noise, longer life and higher efficiency. Depending on what a particular customer’s needs are, low-impact noise could be a primary reason to incorporate a VSD into a machine. Eaton’s pumps are capable of running down to zero rotations per minute, so reduced noise in the overall system—and better overall sound quality—are significant features.

Efficiency is a key driver that brought about Eaton’s variable speed drives solution, and there are several market influencers that have led to innovative hydraulic pump and system level technologies—government regulations and energy costs. Energy costs continue to increase over time, and government regulations are continuing to require fewer emissions, both of which have led machine builders to consider more efficient electric motor solutions. If hydraulic pumps cannot operate in the speed ranges needed to complement the wider speed ranges of VSD motors, they can be replaced by electro-mechanical options.

There’s another part about it, too, which is environmental … as well as being “green” on the cost is the environmental impact of being less likely to have hydraulic leaks around your plant. That’s something that everybody really has to keep a big check on because of its environmental impact.

Lambruschi: The biggest advantage tends to be energy savings. Other types of pumps will see increased controllability, quieter operation and potentially longer life. Drives equipped with fieldbus communications allow for local or remote monitoring of the pumping process, allowing access to parameters like pump loading, running time and energy consumption.

There is such an installed base of hydraulics out there. I think most of the new machine users are not even giving it a second thought of going with the new technology. What’s been slower is driving people to retrofit out their existing working system for something that’s better, more efficient, takes up less room, less oil, less noise, and all the other advantages that it provides.

Meyer: Generally, there are three things that are holding people back from adopting VSD technology—perception, cost and system design. Perception is now the main issue preventing customers from adopting VSD technology, whereas the number one issue in the past was overall cost. Machine builders initially thought a VSD solution for a hydraulic system was extremely expensive. Today, it is equally cost-effective to make a system hydraulic variable speed as it is to make it electric. Hydraulic components don’t change, and electrical components have experienced much lower costs in the past five years. Fixed-speed starters used to be the lower cost, but now variable speed drives are generally the same or lower cost as fixed speed.

Lambruschi: In many retrofit applications with known operating cycles, an estimated payback period can be calculated. In actual applications, this has been shown to be less than 12 months. Cost concerns can also be offset by the fact that many power utilities offer rebates or incentives for the purchase of variable speed drives for pumping applications. Also notable is the fact that cost savings are not just achieved by efficiency, but by less obvious factors such as reduced maintenance costs and enhanced pump life.

Meyer: Duty cycle is key to balancing cost with efficiency. Pumps are capable of multiple speeds, including zero speeds that allow operators to incorporate VFDs—the building block for smart machine architecture. Before you can start designing machine control, you need components that can handle that level of control. If there are cost increases with a VSD, then they must be paid back on the duty cycle.

Lambruschi: Within pumping applications, we see particularly good growth in the use of drives on hydraulic power units, replacing proportional valves and similar technologies with a more efficient approach. Growth is seen in multiple regions globally, with concentrations in areas where new production facilities are being built or older ones modernized.

Nelson: For us, it’s all about ease of use. We offer this solution with our standard sizes and software. We use the same components that we use for most of our typical servo systems, not just our servopumps, like our Sinamics S120 drives, 1FK7 motors and 1PH8 motors.

Lambruschi: Pre-programmed pump application macros and pump-specific parameters, as well as environmental features like conformal coated PC boards, make Parker drives more user-friendly and suited to the tough environments that pumping applications are often a part of. Larger drives used on higher power pumps are constructed with field replaceable power modules, allowing for quick and easy maintenance and minimal downtime in the event of failure. Parker is also uniquely positioned to be a complete system provider, being a manufacturer of pumps, hydraulics, and fluid handling components in addition to variable speed drives.

Meyer: Eaton’s biggest differentiator is low speed—our pump products have been tested down to zero speed. Eaton’s pump products are capable of operating at speeds that are as low as or lower than competitive offerings.

In the past, Eaton pumps or competitive offerings could simply be turned off; however, that function added some complexity to the circuitry. A pump capable of running at zero rpm takes a lot of complexity out of the circuit, in terms of holding pressure. Eaton’s zero-speed capability decreases system complexity and further enables the machine designer to flexibly design the system.

There are some applications where a pump must discharge into a closed system to meet continuously varying demands where a variable speed pump could pay for itself in a short time. But what about water and wastewater systems?

(First, a digression. There is no such thing as a variable speed pump. A pump is a pump. What constitutes variable-speed pumping is a variable-speed motor attached to a pump. A variable frequency drive (VFD) is the best technology these days to produce variable speed. So, I’ll call the pump, VFD and motor together as a variable speed pump.)

The selection of the pumping technology should be based on life cycle costs (plus some other considerations) and depends heavily on the nature of the pumped system. There are essentially two types of systems – those that have floating storage and those that don’t. This makes a big difference in the type of analysis required.

Systems with storage have a significant advantage in pumping in that it is possible to turn the pumps(s) OFF. This storage can refer to an elevated water storage tank or a sewage wet well. If you correctly select the right constant speed pump, you can run it at an efficient operating point to fill the storage tank or drain the wet well and turn it off. I’ve done a lot of calculations along these lines, and constant speed pumping almost always wins.

But as with everything else in life, there are exceptions to the rules. The first exception depends on the shape of the system head curve. Most water, and to a lesser extent, sewage pumping involves a fairly flat system head curve. Water is lifted from one pressure zone to the next higher one or lifted over a drainage divide. It is very difficult to turn down the speed without seriously hurting the efficiency. However, if you are pumping across flat ground, most of the energy is used to overcome friction, and the flow can be adjusted without having as much detrimental effect on efficiency. The friction-dominated case may favor a variable speed pump.

In systems without storage, it’s not possible to turn pumps off, so the pump station must meet the instantaneous demand. This means that during low demands, a constant speed pump would need to run far to the left on its curve and the pump would be pumping at a high head and low efficiency. A variable speed pump would be the clear winner—but not always.

The pump station must meet peak demand with the largest unit out of service. The typical configuration for a small to medium pump station is usually two pumps, with each sized to meet peak demands. But, in most situations, the peak demand rarely occurs, and the one running pump is running at low efficiency, especially during low flow periods.

Is there a better configuration than these two pump solutions? Enrico Creaco and I (Walski and Creaco, 2016) tested a wide range of configurations (see below) over a wide range of flow in a paper we wrote using WaterGEMS to calculate life-cycle energy costs.

As expected, the configuration with two constant speed pumps had the worst life-cycle cost. But surprisingly, the second-worst was the two variable pump setup that pretty much everyone uses. Configurations with three pumps (or for very small systems, two pumps, and a hydropneumatics tank) proved to be better than two variable speed pumps. All the three pump configurations were fairly close to one another in cost. The reason they were so good was that their best efficiency point could be matched fairly well with the most common demands with only one pump running. For those cases, where demands were high, simply turn on the second pump until the demand drops.

A lot depends on the actual flow distribution that the pump station will encounter. If the peak flow is 800 gpm and the average flow is 750 gpm, then any configuration will work well. However, if the peak flow is 800 gpm and the average flow is 200 gpm, then it will be virtually impossible to make the two-pump designers work efficiently.

In an earlier blog (Abusing Affinity, 4 March 2021), I mentioned how the calculations of head and efficiency for variable speed pumps are governed by the pump affinity laws, and sometimes those folks selling VFDs misrepresent the affinity laws to make their product look more beneficial than it really is.

Another issue is the fact that the VFDs themselves introduce a certain amount of inefficiency. They work by breaking up the smooth sine wave of alternating current into pieces and reassembling those pieces in a sine wave with a lower frequency, thus varying the pump speed. The problem is that this reformulated output wave is less than 100% efficient. This loss of efficiency is sometimes called the “parasitic energy demand of the VFD”. VFD salespeople don’t like to talk about this, and if you ask them for data about VFD efficiency, they will only provide data at 100% of full speed, which is not the case you’re looking for, or respond along the lines of.” Hey, do you think the Chiefs will win the Super Bowl next year?”

How do you decide on the best configuration for your pump station? I’ve been trying for years to come up with some rules-of-thumb to decide on the best configuration, and the best I could come up with are the paragraphs above.

What you need to do as a conscientious engineer is try many designs to arrive at the best pump selection. The most tedious step in a good evaluation is calculating the life-cycle energy cost because the pumps must work over a range of conditions. In my early days, I did these calculations manually, and you needed to make a lot of simplifications to make the effort feasible. Later, I graduated to spreadsheet calculations, but that still didn’t capture all the hydraulic and cost variability. Now, if you start with a well-calibrated model, WaterGEMS and WaterCAD can give you the results you need with a few mouse clicks.

Walski, T. and Creaco, E., 2016, “Selection of Pumping Configuration for Closed Water Distribution Systems”,Journal of Water Resources Planning and Management,142(6), DOI: 10.1061/(ASCE)WR.1943-5452.0000635.

From commercial HVAC systems to wastewater and water treatment facilities, many industrial and commercial pump applications require powerful and durable pumps to efficiently move fluids. Imagine if every one of those pumps was powered by a motor designed to increase efficiency and improve system reliability, delivered in a form factor that is significantly smaller and lighter than a traditional motor. Sound impossible? It’s not. Infinitum has you covered. Our motors also offer additional flexibility for pump applications through the integrated variable frequency drive (VFD) and our optional Internet-of-Things (IoT) capabilities, making it straightforward for facility managers to program and monitor pump performance while optimizing for wire-to-water efficiency.

Our motor-mounted variable frequency drives INVEOR MPPandINVEOR MPoffer you the best of both worlds thanks to the fast PID process controller: Short cycle times for changing pressure at speed as well as the ability to maintain constant pressure conditions for a long period and with precision. The additional overload of up to 200 percent also makes the highest starting torques possible, meaning that there are always sufficient reserves even for strong back pressures. This makes our INVEOR variable frequency drives the all-round solution for controlling the pressure of all hydraulic pumps.