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The issue with Danfoss H1P pumps for fan drive

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.