Variable Speed Hydraulic Pumps Enable Efficient Machine Operation
What you’ll learn:
- The benefits of using variable speed hydraulic pumps.
- How advancements in motor technology are improving variable speed hydraulic pump designs.
- Factors driving uptake of variable speed hydraulics in industrial machinery.
Use of variable speed hydraulic pump technology in industrial machinery has gained momentum over the past decade due to the energy savings it can provide. Electricity and other energy costs continue to rise around the world, prompting many machine owners to place a greater emphasis on use of efficient systems and machines to lower these costs.
According to Neal Gigliotti, Senior Application Engineer at Bosch Rexroth, variable speed hydraulic pumps were first adopted in plastics processing machinery. Plastics processing is a very cost-sensitive market, he said in an interview with Power & Motion, so any savings are appreciated.
As the energy savings and other benefits of the technology became apparent, additional industries began to adopt variable speed hydraulic pumps into their machines as well, and use of the technology continues to grow in various markets due its many advantages and ongoing technological developments.
The Advantages of Variable Speed Hydraulic Pumps
Gigliotti said variable speed hydraulic pump technology is exactly what it sounds like — it is a pump with varying speed capabilities.
Traditionally, hydraulic pumps used in industrial machinery run at a fixed speed. He explained this is different from mobile hydraulics applications which typically run at the speed of the diesel engine which has variable speed.
“Industrial machinery has typically run fixed speed electric motor power, which is fine, but not super efficient,” he said. “If you’re not doing any work for a period of time, but you're spinning a hydraulic pump at maximum speed as if you need it, you're consuming energy to do that, making it not very efficient, unless you happen to be needing maximum power all the time.
“By changing the system to vary the speed of the electric motor based on the demand of the hydraulic system or the demand of the machine that's being driven by the hydraulic system, you can greatly increase efficiency of the system,” said Gigliotti.
If, for example, you only need half of the flow of the pump, you can slow the motor down to half of the speed. “Therefore, the pump is operating at its best efficiency, even though it's only supplying half the flow, because it's running at half the speed,” he said.
Gigliotti notes that this helps to cut down on heat generation in the system because you are no longer unnecessarily spinning the moving parts of the pump at maximum speed all the time. “Spinning of the parts creates friction and heat inside the pump, which can degrade the life of the equipment faster,” he explained. “If you slow the speed down when you don't need the flow, you don't have all that extra wasted energy and heat in the pump, so pump life tends to improve with variable speed [technology].”
Electrical energy use is lowered as well, reducing machine operating costs. In addition, variable speed technology is quieter.
In the U.S., traditional hydraulic pumps on industrial machinery are typically run at 1,200 or 1,800 rpm. He explained that a hydraulic pump running at 1,800 rpm is fairly loud which can make for an uncomfortable working environment for those near industrial machinery.
“If you reduce the speed of that pump during idle to 500 rpm or lower, you can't even hear it run,” he said. “So, if you have idle time for a significant part of a machine cycle, your average sound of the machine is greatly reduced.”
Gigliotti said the main improvements variable speed hydraulics provide are in the areas of energy savings, heat savings and noise savings. “There’s also ancillary savings,” he said. “If you're not generating as much heat, you don't need as much cooling capacity on the system either to remove that heat.” This can help reduce installation and operating costs as well as overall machine size.
Servo Motor Driven Hydraulic Pumps Will Bring Further Gains in Efficiency and Control
For many years, standard induction AC motors have been used to drive both traditional and variable speed hydraulic pumps. But advancements in permanent magnet servo motors are making them a more viable option, and their use is increasing in some applications and industries.
The key advantage of servo motors is their ability to react quickly and be controlled actively to vary the speed and limit the pressure of a hydraulic pump, said Gigliotti. “[This means] you don't need a very expensive hydraulic pump with intelligence on it that controls the oil flow to the system,” he explained. “All that intelligence can be [done with] the servo motor and drive so you can use a basic type of pump that costs less [and is] simpler because all of the high-level control will be done by varying the speed of it.”
This allows for the creation of an energy-on demand type of circuit. In this scenario, if you have a hydraulic cylinder run by a servo motor driven pump, there is no energy being consumed when the cylinder is not moving. But as soon as the cylinder starts to move, the motor spins to drive the pump at the speed required to get the necessary velocity of the cylinder.
“The speed of the motor is exactly matched to the speed of the hydraulic device that it's connected to,” said Gigliotti. “It goes literally from zero to maximum speed as they need it, [and] it's perfectly matched to the amount of energy required to do the work.”
He said a conventional motor cannot react like that. A standard AC motor spins whether you need it to or not; even though at a reduced speed if idling, the motor is still spinning. “It doesn't have the capability to go to 0 rpm and then react fast enough to come back up to speed.”
Permanent magnet servo motors, on the other hand, are more efficient and able to provide higher levels of control with simpler hydraulic pumps. Advancements in servo motor technology over the years have made them larger and more capable, and thus more relevant for use with hydraulic systems said Gigliotti.
Bosch Rexroth has begun using servo motors with its variable speed systems due to the advantages the company sees this motor technology providing. He said the company has developed pumps that are directly coupled to a servo motor, eliminating the need for any additional connection devices such as couplings. This helps to create a more compact system that is easier to install.
In addition, he said because servo motors are smaller than conventional AC motors, the company has also been able to develop pumps that can bolt directly to hydraulic manifolds without the need for high-pressure piping or hoses in between. “It's allowed us to develop new styles of pumps that let us do more because they're designed to work with servo motors specifically.”
Not only can these more integrated designs create a smaller overall hydraulic system package size but they can also reduce the amount of oil required to operate a machine. “You don’t need a large reservoir,” said Gigliotti. “If we do closed loop control over the hydraulic circuit, you can use a very small hydraulic reservoir, [reducing] how much oil you need to have in your machine. So, it saves cost, it saves complexity, and it saves having a lot of oil in the machine.”
In addition, he said this type of design reduces the costs associated with manufacturing a machine because the need for expensive welded high-pressure piping and hoses has been eliminated by directly mounting the pump onto the hydraulic manifold.
“It opens up possibilities that didn’t exist before. That’s basically thanks to the revolutions that are coming along by applying variable speed technologies,” he said.
Market Factors Driving Uptake of Variable Speed Hydraulics
While variable speed hydraulic pumps offer many advantages, the technology remains a more expensive solution than traditional hydraulics. However, Gigliotti noted the cost of variable speed technology began to come down about 15 years ago to a point where it made sense for some industrial customers to utilize.
For machine owners in cost-sensitive applications such as plastics processing, the long-term energy savings potential outweighed the initial costs of variable speed solutions which helped drive its uptake in this market. Another factor that prompted the plastics processing market to adopt variable speed hydraulics was the fact that two competing technologies were being used in machinery — hydraulics and electric drive.
Gigliotti explained that hydraulics provided a robust and dependable option for this market but was not as efficient because it was fixed speed. Electric drive offered a more efficient option that also did not produce as much heat and noise, but had a much higher initial installation cost. “You had these two competing technologies already installed in the plastics industry. So, when the variable speed technology was applied to hydraulic pumps in a commercially viable way, they immediately adopted it in that industry, and it almost transformed that industry overnight,” he said.
Within 1-2 years, almost all new plastic injection molding machines had transitioned to variable speed hydraulics he said. Conventional hydraulics were almost gone and the number of electric drive machines declined because variable speed hydraulics “gave you the best of both worlds.”
Visit EndeavorB2B partner site Plastics Machinery & Manufacturing to learn more about injection molding and other machinery utilized by the plastics industry.
Variable speed hydraulics pairs the advantages of hydraulics with the advantages of electric drive and does not cost as much to build as an all-electric machine, said Gigliotti.
Despite these advantages, he noted other industries were not as quick to adopt variable speed hydraulic pumps. Over time though, machine builders increased their use of the technology due in part to regional customer preferences.
In Europe, for instance, the cost of electricity is high and therefore use of variable speed technology can greatly reduce operational costs. It has thus become the technology of choice for many machine builders in the region because of the cost savings it can offer customers. And as their machines were exported to other parts of the world, customers in various regions such as the U.S. began to see the advantages as well.
This has in turn led machine builders around the world to begin adopting variable speed hydraulic pumps to serve domestic customers and those in export regions to remain competitive with those already using the technology.
In general, Gigliotti said variable speed hydraulic pumps are a good fit for any type of industrial machinery application except for those running at maximum power all the time. He noted a hydraulic-powered fracking truck as an example. When in operation, it’s running maximum power all the time and has no idling or dwell time during which energy could be saved. “It would actually be less efficient to try to put a variable speed drive on it than just running it with a fixed speed electric motor,” he said.
“Those applications are the minority of applications in industrial machinery,” he continued. “The majority of them have defined cycles or idle periods in the cycles, places where you're going to save energy.”
Gigliotti anticipates use of variable speed hydraulic pumps will continue to grow and that eventually the vast majority of industrial machinery will use the technology instead of fixed speed drives. “[There is] too much of an energy savings potential,” that will benefit customers in a range of applications, he concluded.
About the Author
Sara Jensen
Executive Editor, Power & Motion
Sara Jensen is executive editor of Power & Motion, directing expanded coverage into the modern fluid power space, as well as mechatronic and smart technologies. She has over 15 years of publishing experience. Prior to Power & Motion she spent 11 years with a trade publication for engineers of heavy-duty equipment, the last 3 of which were as the editor and brand lead. Over the course of her time in the B2B industry, Sara has gained an extensive knowledge of various heavy-duty equipment industries — including construction, agriculture, mining and on-road trucks —along with the systems and market trends which impact them such as fluid power and electronic motion control technologies.
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