By Tom Stone
When you think about it, getting people and businesses to acknowledge the benefits of increasing energy efficiency is an easy sell. Really, are there any people or companies out there hoping that their utility bills—be they for heating, water or electricity—continue to go up? No. But as with any change that needs to be made after years of living with the status quo, the hard part is finding the best way to make these sought-after energy-efficient improvements.
When considering the manufacturing sector, energy costs continue to rise around the world while the demand also increases for companies to improve profitability through greater cost controls. Reducing energy consumption has become a key component in controlling costs at manufacturing facilities around the globe as higher energy costs impact every company’s—and country’s—bottom line.
Now that the goal has been identified, the time has come to find, develop and implement the best ways to make the manufacturing sector—specifically its pumping systems—as energy-efficient as it can be.
The Challenge
As spelled out in “Improving Pumping System Performance: A Sourcebook for Industry,” a joint effort between The Hydraulic Institute and the U.S. Department of Energy’s Energy Efficiency and Renewable Energy (EERE) Program, poor design and improper system operation are at the root of inefficient pumping systems. As rotating equipment, pumps are subject to wear, erosion, cavitation and leakage. These problems can be exacerbated through improper pump selection and operation. If they are not selected or operated properly, pumps can waste enormous amounts of energy, as well as require considerable maintenance.
Selecting the proper pump for each of the myriad operations in a manufacturing facility can be a daunting task. This selection process is further complicated by the fact that many different types of pumps can be applicable for a single operation. And when making the final choice in type of pump, several crucial factors may need to be taken into account: required flow rate, suction and differential pressure, temperature, viscosity, corrosiveness of the liquid being handled, etc. In addition, facility managers too often choose oversized pumps when outfitting their systems under the incorrect belief that such equipment will address future capacity needs. These decisions ignore the added energy costs inherent in operating oversized pumps.
At the most basic level, the choice when outfitting a pumping system most often comes down to selecting between a positive-displacement (PD) or centrifugal-style pump. While the majority of the world’s pumping tasks may currently be performed with centrifugal-style pumps, more and more facility managers and operators are becoming aware of the benefits—among them energy savings—that are found in pumps that take advantage of sliding vane technology.
In fact, by virtue of their inherent energy- and mechanically-efficient designs, positive-displacement sliding vane pumps are uniquely suited to offer managers immediate high-value advantages and solutions in fulfilling their energy-saving initiatives. Although the operating principles of PD and centrifugal pumps differ widely, in many cases both designs can be used for the same services. In these “overlap” applications where either PD or centrifugal pumps may be used, choosing positive-displacement technology can result in improved processes, uptime and energy savings. In looking at a list of the most common system characteristics that need to be considered in a pumping application, PD pumps outperform their centrifugal rivals in almost all of them.
Depending on the technology chosen, PD pumps may offer:
• Constant flow, relatively, independent of changes in system pressure
• Constant flow, relatively, independent of changes in pumpage viscosity
• Ability to pump high viscosity products
• Ability to handle entrained gases
• Ability to self-prime
• Ability to line strip
• Ability to run dry for short periods
• Higher efficiency across varying system pressures
Since PD pumps maintain higher efficiencies through a wider range, when considering the overlap where both types of pumps can operate, a PD pump’s higher mechanical efficiency may result in greater energy efficiency than a centrifugal pump’s.
So, while positive-displacement pumps clearly offer a long list of operational advantages when compared to centrifugal-style pumps, within the PD family of pumps itself sliding vane technology also reigns supreme. This white paper will focus on the benefits of Sliding Vane vs. Gear positive-displacement pumping technologies.
Possible Solutions
Positive-displacement pumps pressurize fluid with a collapsing-volume action, essentially moving an amount of fluid equal to the displacement volume of the pump with each shaft rotation. As such, PD pumps have what is called a “fixed displacement volume,” meaning that the flow rates they generate are directly proportional to their speed and the pressures generated are determined by the system’s resistance to this flow.
These characteristics make PD pumps very appropriate for applications that feature working fluids that are viscous; systems that require high-pressure; low-flow/high pressure requirements; flows that must be precisely controlled; or when high pumping efficiency is desirable.
Within the family of positive displacement pumps there are numerous different types or technologies available. Sliding vane and gear pumps are two of the most widely used rotary types: here’s a closer look at both:
Gear Pumps
Simply put, a gear pump uses the meshing of gears to pump fluid by displacement. As the gears rotate, they separate on the intake side of the pump, creating a void, which is filled by the fluid that is being handled. This fluid is transported by the gears to the discharge side of the pump where the meshing of the gears forces the fluid to exit the pump through the discharge port.
Gear pumps can be further divided into external gear pumps and internal gear pumps. While the pumping action for both is comparable, external gear pumps utilize two similar rotating gears to mesh whereas the internal gear pump utilizes a drive, or rotor, gear operating against a smaller internal, or idler, gear.
Because of their style of operation, from day one gear pumps wear constantly as the pump’s gears mesh together in order to move fluid. This constant wear increases the internal pumping clearances in the process reducing flow capacity and volumetric consistency by increasing the “slip” within the pump (the movement of the fluid being handled opposite of the direction it’s being pumped). To compensate for these larger clearances—and the operational problems that they cause—the pump speed or size must be increased, which not only increases energy consumption, but also further accelerates the pump’s wear. The other alternative is to live with reduced pumping capacity until the pump’s performance drops to an unacceptable level.
These wear conditions can often go undetected, sapping the pump of efficiency—both energy- and performance-related—for a long period of time before the necessary maintenance is performed. As reported in The Hydraulic Institute’s “Testing for Pumping System Efficiency Tip Sheet,” “A (gear) pump’s efficiency can degrade as much as 10% to 25% before it is replaced, according to a study of industrial facilities commissioned by the U.S. Department of Energy, and efficiencies of 50% to 60% are quite common. However, because these inefficiencies are not readily apparent, opportunities to save energy by repairing or replacing components and optimizing systems are often overlooked.”
The degradation of internal clearances is also a trait found in centrifugal pumps, leading to a reduction in operational and energy efficiencies.
Sliding Vane Pumps
As opposed to gears meshing together, sliding vane pumps operate through the use of a number of vanes that slide into or out of slots in the pump rotor when the pump is rotating. The vanes move outward from the rotor and ride against the inner bore of the pump casing, in the process forming pumping chambers. As the rotor revolves, fluid enters the pumping chambers from the suction port. The fluid is transported around the pump casing until it reaches the discharge port where it is forced out into the discharge piping. This type of design virtually eliminates slippage, meaning that the pump’s high volumetric efficiency is maintained.
Because the self-adjusting sliding vanes continuously adjust for wear, sliding vane pumps are able to maintain near-original efficiency and capacity throughout the life of the pump. The pump speed also does not need to be increased over time, making sliding vane pumps inherent energy-savers.
If the sliding vanes do wear out, or are damaged, replacing them is easy and quick. Replacement of vanes can be quickly accomplished by removing the outboard head assembly, removing the old vanes, inserting new ones and reinstalling the head, all without the need for special tools. In a matter of minutes, the pump is back in operation. Sliding vane technology—which Robert Blackmer invented in 1899—continues to be improved upon to this day by Grand Rapids, MI-based Blackmer. Sliding vane pumps manufactured by Blackmer are used in a wide variety of process and transfer applications within numerous markets, such as: chemical process, crude oil, refined fuels, biofuels, pharmaceuticals, cosmetics, food processing, health care manufacturing, pulp & paper, wastewater, military, commercial marine, soap & detergents and paint & coatings.
Blackmer manufactures multiple lines of sliding vane pumps, each with areas of primary applicability. Combined, they range in size from 3/4-inch ports to 10-inch ports with flow rates ranging from 1 gmp (3.8 lpm) to 2,200 gpm (8,328 lpm) with a maximum viscosity of >500,000 SSU (108,000 cP).
Conclusion
Sliding vane technology is being used worldwide to reduce energy cost and consumption, and create more efficient pumping systems. In the chart, a comparison between the performance of sliding vane and gear-pump technology shows some of the many ways that sliding vane pumps can improve your operation.
This leading-edge technology solves everything from suction, product shear and volumetric-efficiency problems to offering unique benefits such as line-stripping capabilities and metering —all while saving energy. These characteristics make sliding vane pumps a key component of Blackmer’s Smart Energy Program, which emphasizes the ability of its positive-displacement pumps to increase the energy efficiency of plants where pumping systems are in operation. Simply put, sliding vane technology offers numerous advantages in the quest to reduce energy consumption and cost without sacrificing performance, making them the perfect positive-displacement pump choice in these increasingly energy-conscious times.
Questions can be addressed to Blackmer at (616) 241-1611. For more information regarding Blackmer products, go to blackmer.com.