Fluid Power Journal

Power Factor…An Opportunity

I know, I know, you’re tired of having to think about energy, and you can’t find your calculator. We’ve covered a lot of bad news about our fluid power systems, and you’re feeling discouraged. Well, I have some good news! What we just learned about power factor can provide an excellent and relatively untapped opportunity to apply fluid power.

You see, we are not the only ones who specify oversized electric motors in our applications. As a matter of fact, nearly all manufacturers do the same thing. If 10 kW will do the job, they will put on a 20 kW motor, just to be on the safe side. The result is that almost every industrial facility is loaded with electric motors that are oversized for the job they are performing. There are exhaust fans, water pumps, conveyors, and blowers, all with oversized motors. Each motor requires an electrical cabinet to hold the starter, circuit breakers, maybe a start/stop button, and an “E Stop.” Often the cost of the starter and controls will approach or exceed the cost of the motor itself. The power factor that is accumulated by this array of motors pushes up the cost of electricity to these industries. We can help!

Now, some of you are going to get a little nervous about what I am going to say next, but before you get too upset, listen carefully and then do the math. Remember, this is just a suggestion, a potential opportunity that we ought to have at least explored.

The basic premise is this: one properly sized electric motor supplying power to a number of smaller systems has a lower installed cost and lower operating cost than the combination of all the small motors that would be required to drive those same systems. It follows then that using a properly designed central hydraulic power unit supplying a variety of hydraulic motors can replace a bunch of smaller electric motors and with a reduced installed and operating cost.

Now, in order to make this work, we, the Fluid Power Professionals, will have to really do our homework. Reject the “rules of thumb.” Forget the “fudge factor.” Shun the shortcut. This is not going to fall into our laps. We are going to have to work for it, but in the end, it will be in the best interest of those who have put their trust in our abilities. It will help reduce costs, make better use of energy, and help establish the image of Fluid Power Professionals as “Energy Professionals.”

So, where do we begin? First of all, think about the things you already know about fluid power. We can take a single power source and transfer the energy to perform linear and/or rotary motion. We can build in soft starts and torque limiting, not to mention reversibility. We can operate in hostile environments and can be used under water. We are equally happy with high-speed and low-speed applications without the use of gear reductions.

Second, find the right application. It can be really difficult to make changes to an existing system. Management is usually reluctant to try something new on a system that is already working. Try to find a new application or an old system that is ready for an upgrade.

I worked at a plastic blow-molding facility for a while. There were 16 molding machines, and each had its own grinder that was used to reclaim the material that was trimmed during the process. Two additional grinders where used to shred other discarded plastic material. There was a blower system on each machine that conveyed the trimmings to a specific grinder so as not to mix the materials. The grinders were belt driven to reduce the knife speed to 600 rpm, and each was powered by a 7.5-kW electric motor. This gave them enough muscle to chew up large quantities of plastic if necessary, but most of the time, only a few small pieces of trim were conveyed to the grinder. The grinders spent about 1% of the time under heavy-load, 20% under no-load, and 79% under low-load conditions.

I also had an opportunity to do a study at a water treatment plant. It had six 7.5-kW motors connected to gear reducers driving centrifugal water pumps. There were also two 38-kW motors connected to gearboxes driving circulating pumps. The system operated 24/7.

Both of these facilities provide an excellent opportunity to demonstrate the advantage that Fluid Power Professionals can bring to the table. It was shown that both companies could save about $30,000 a year in energy costs if they switched to central hydraulic power systems.

So, how would you, as a Fluid Power Professional, approach these challenges?

Well, I’m not going to do the math for you, even if you whine about it. I will, however, discuss some steps you could take, depending on your relationship with the facilities.

Let’s say you are a Fluid Power Professional who is the facilities manager of one of these companies. You’ve been reading these articles and are convinced that it would be in the best interest of the company to make the fluid power choice. Where would you begin?

The hardest step is overcoming the inertia of “We’ve never done it that way before.” At both facilities, it would be best if you can get in at the planning stage for a new installation. 

At the molding plant, you can tell the grinding machine manufacturer that you want a quote on the equipment with hydraulic motors driving the knives directly and with no belt drives for speed reduction. You want a central hydraulic power unit that can handle the average load of the combined motors. You want directional valves that will allow you to reverse the motors (something the original grinders cannot do) because sometimes material gets stuck in the knives, and without the reversing capability, you will have to disassemble the grinder to clean it out.

At the water treatment plant, you would let the contractor know that you want an alternative approach using a central hydraulic system driving the water pumps without gear reduction. You will probably have to get the contractor to give you the model number of the water pump, so you can call the manufacturer and find out what the actual input torque requirement is. The literature on the water pump will probably only tell you the suggested input horse power. What you need to know is the actual running torque without going through a reducer. This may take a little pushing because the manufacturer is not used to being asked that kind of question. You may wind up talking to some lonely engineer in a back room somewhere who keeps that sort of information either in her head or in a box under the desk. (Oops! Did I say that out loud?) As I said, this is not going to fall into your lap. You will have to work for it, but it is worth the effort.

If you happen to be a Fluid Power Professional involved in application engineering, then you can approach the OEMs and let them know that you can help them in marketing their equipment by introducing central fluid power as an alternative.

If you are attempting to make changes in an existing system, there are some basic things you will need to do whether you are the facilities manager or the sales person. Find the actual torque and rpm rating for the driven components. From this, calculate the theoretical kW to operate the machine. Then contact the local power company, and have them place meters on the machines to give you the data on the actual power usage and get a report on the power factor. With this information, you will be able to calculate the current cost, the potential savings, and environmental benefits of the new system.

In all cases, you will need to be able to accurately and convincingly defend the benefits of fluid power including efficiency, reliability, and flexibility.

Some utility companies are offering incentives to make systems more efficient. Contact your local utility and find out what is available. This information, along with your Fluid Power Professionalism, will help you see the power factor as an opportunity.

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