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Articles about hydraulic, pneumatic, lube, etc. systems design.
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Charge pump displacement

November 12, 2019 0 Articles , , , 817 Views

Close loop circuit

There is a generic rule for close loop systems, to select the charge pump size: pump displacement should be at least 10% of the combined displacement of the pump and motor. To understand where this value comes from let’s figure-out all factors in the system what influence on a charge flow:

1. The charge pump has to supply enough flow to compensate for leaks due to the volumetric efficiency of the pump and motor. This is why sometimes the charge pump called a “replenishing pump”.

In general, volumetric efficiency of pump and motor in the hydrostatic transmission is around 96..97%, so system overall volumetric efficiency is around 93%. It means 7% of the theoretical pump flow is the leaks which need to be somehow compensated.

2. Addition flow needs for flushing of both main pump case and motor case to remove the hottest oil from the system.

Adding a hot oil shuttle valve at the motor removes the hottest oil in the loop through the motor case drain. Normal practice is to run the motor case back to the bottom drain port of the main pump then from the top pump’s drain port to the cooler (see the picture above).

There no ways to calculate exactly the required flushing flow through the motor. You need some experience with different applications and motor sizes, you have to do tests and check recommendations from the motor manufacturer. The generic rule to find the best flushing flow rate: motor should not be overheated in the worst-case mode.

3. Charge pump itself has huge internal leaks.

Mostly charge pump is a vane or gear type, and the volumetric efficiency of these type of pumps is very low, around 80%.

4. A small qty of flow is required to power the pump’s control system.

This qty of flow is pretty small.

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Of course, different systems require different approaches to the calculation of charge pump displacement. And sometimes we have to make some compromises. If you have doubts – just ask a question!

SUN Hydraulics – delivery time issue

October 28, 2019 2 Articles , 750 Views

SUN delivery issueWorking on the design of new projects I like to involve SUN Hydraulics valves and use them a lot. They are not expensive, pretty reliable and have uncredible understandable paper and online catalogs.

All these major benefits coming to naught as soon delivery time even of very wonderfull products makes impossible to use them in projects. This is exactly what going on these days.

Today I got a quotation from a local vendor for the valve FDEA-LAN with delivery time 31 weeks!!! It is longer than my project needs to be completed!

Helios Technologies (formerly known as Sun Hydraulics) has three facilities in the Americas, two in Europe and already three in Asia-Pacific (one more plant in China has been opened this year). But this fact doesn’t help to provide SUN valves faster.

Because the company, where I’m working now, has fillies in Europe we know the issue with the SUN product delivery time is currently common for the whole world. There no any comments from SUN and its parent Helios at their websites and I see the delivery time is increasing every month.

Therefore, I’m seriously starting to think about solutions on how to proceed. Problem is a lot of manifolds that have already been designed in our projects use SUN cavities. And to re-design of these manifolds is a pain, you know why. I’m seriously thinking to use SUN clones to cover these positions. Currently, I dug the next manufacturers:

  • Winner Hydraulic. This is a manufacturer from Taiwan, but they do not have distributors in North America.
  • PressureBoss Hydraulics Inc. From their website is not clear what country their plant is physically situated. They have distributors in the US but not in Canada.

For new projects, I’m starting to look at Parker and Eaton cartridges. They have a pretty good assortment and actually last months I already used some of their valves as quick replacement options.

How you are dealing with SUN Hydraulic delivery issue?

The issue with Danfoss H1P pumps for fan drive

August 30, 2019 0 Articles , 728 Views

Danfoss H1P issue

I like H1P close-loop pumps for mobile applications: they are very compact, have a small weight, pretty reliable and very easy in an adjustment of any its settings.

But I met one undocumented issue during the experience with these pumps: the max work pressure at fan drive applications. These small displacement pumps (45cc, 53cc and 60cc) can not produce full flow and work stable at the high-pressure range. I made a request about this to Danfoss and got the next responses:

We’ve had experience running these smaller frame H1 pumps on fan drives at full working pressure in the past. What we’ve found is, the pump swashplate sometime is unable to overcome the forces necessary to keep itself at full stroke. Even though the pump control is commanding full stroke, it may not go all the way (the 53cc frame size is the worst size for this).

The reason the pumps can’t reach their rated pressure in these applications is due to the nature of the H1 fan drive control. It is a non-feedback control, meaning there is no link between the position of the swashplate and the pump control. Thus, the swashplate position is susceptible to changing based on the system pressure.

The challenging part is, this isn’t consistent across all pumps. Depending on how the tolerances stack up on an individual pump, one batch of pumps may work perfectly fine at the high working pressure and another may not. Based on our previous experience, we wouldn’t support a fan drive application at full rated working pressure.

Therefore I asked about max work pressure these pumps can provide full flow and got these data:

  • 60cc pump can work stable up to 350 bar
  • 45cc/53cc pumps can work stable up to 280 bar

Again, this issue is only for fan drive control system (FDC) where swashplate goes to full displacement upon loss of the control signal. The simple EDC control system does not have this operating pressure issue.

Therefore, like options, we can either select bigger displacement pump or different brand. Good to know for system design, right? But you can not find this info in Danfoss pumps catalogue.

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