One of my favourite guidelines for design: “Keep it simple. Simple and clever”. Bosch Rexroth demonstrates this with their Frequency Controlled Pump (FcP 5020). We get significant energy savings while keeping it simple. It really is a clever innovation!

  • Bosch Rexroth FCP 5020 – Pump & Motor Combo with Pre-Programmed VFD

I’m talking about the combination of a variable frequency drive (VFD) with a standard (asynchronous) motor and a gear pump. In this package from Bosch Rexroth, you also get a pressure sensor and some excellent software in the VFD. As a result, you can set the hydraulic pressure you want in the software and this will function like a pressure compensated pump. 

When I first heard about this, I thought:  “Why on earth would I want to do that with a gear pump? Surely a piston pump with a pressure compensator will do a better job of this than a gear pump! That is, it would respond faster and be more accurate at maintaining the pressure setting.”

Check With the Expert

So I decided to ask Rodney Trail of Bosch Rexroth Canada. Rodney has been specializing in the application of these Sytronix (variable speed pump drive) technologies since 2007.

As it turns out, I was partially correct. The pressure compensator on the piston pump can respond quicker than the gear pump /motor combo. That’s because the gear pump and motor have to increase, or decrease speed in order to maintain pressure, while the piston pump just changes position of the swashplate. However, if the piston pump also needs to change speed in order to maintain pressure, then the difference in response time is barely noticeable. This is because the piston pump has a higher inertia than the gear pump, which makes it more difficult to accelerate.

The advantage of the gear pump is, that it simplifies the controls. “Keep it simple”. That is, there is no pressure compensator to adjust. The pressure setting is simply a parameter setting in the VFD. That also makes it easy to change the setting for anyone with a laptop and the required cable.

Improved Reliability (uptime)

For these systems, Bosch Rexroth uses the internal gear pump series PGF & PGH. In addition to being very quiet & efficient, there are fewer parts in these pumps than in a piston pump. There are no pistons, slipper pads, swashplate, cradle bearing or control valve.  Fewer parts in motion means fewer parts to fail => more reliable.

Ease of Troubleshooting

Troubleshooting also becomes much simpler.  There is no variability in the pump to consider.  If the pump is turning and it’s not pumping oil, then either there’s no oil getting to the suction port of the pump, or the pumps is faulty. Simple. No control valve setting to adjust, or check.

Improved Efficiency

Since there is no controller, there is no leakage through a controller. This can be significant during those times, when you’re just holding pressure. Thus the heat generation is also reduced, reducing the need for cooling.

Reduced Cost

Obviously, a gear pump costs less than a piston pump. Therefore, the cost of the system is reduced, making this a very cost effective way to create a very efficient, quiet power unit.

Other Benefits

Just like the DRn system I talked about in blog number 4, the benefits are:

  • Significant energy savings with each pump motor group
  • Lower cooling capacity required
  • Better working environment due to lower noise levels
    • this could even reduce your insurance costs
  • Improved Control
    • Feedback devices such as oil level, oil temperature, etc. can be wired into the VFD. From there they can be monitored anywhere in your network via the multi-ethernet capability.
    • Maintenance personnel can receive early warning of a problem without walking to the power unit
  • Longer pump and motor life due to lower average operating speed
  • possibly allow you to increase your production machinery without increasing your power feed lines

All of this while keeping it simple! With the intelligent software provided within the VFD, the setup is quick and simple. That means you can be up and running in no time.

Want Even Better Performance?

For improved performance with a gear pump, replace the asynchronous motor with a servo-motor (synchronous motor) and keep the VFD. The servo-motor has much faster acceleration times, while using the VFD keeps the costs down. Bosch Rexroth calls  this the FcP 7020.  If we replace the VFD with a servo controller, then it becomes a high performance unit, called the Servo Controlled Pump, or SVP 7020. We’ll cover that in a future article.

What are your thoughts? Does this sound like something you, or your customers can benefit from? Any questions? Please let me know in the comments below, or send me an email (burk@burkschmidt.com).

Other Options

The above pump drive combination is the one of seven options for a modern hydraulic power unit. If you want to see six others that I’ll be writing about, you can download the preview summary via this link.