FluidPower.Pro

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.

Manifold for motors in close loop.

Just a note about one direction motors (not reverse!) in close loop applications.

There are a lot of different ways how to proceed with a hyd. motor in close loop applications to make motor work safe and reliable. From my experience, almost each one direction motor application is required to have the next items:

  1. Anti-cavitation check valve
  2. Pressure relief valve
  3. Case flushing valve
  4. Test ports

Each motor manufacturer has own solutions for their motors, but here are problems you can meet:

  1. OEM solution usually is not flexible: you can use only what they have. If you need for example flushing of the motor case – you have to design something external anyways.
  2. Price for these options is unreasonably high;
  3. Delivery time increased on 2..6 weeks;

Here is how I like to proceed for one direction motors – with an external manifold, mounted by hoses flange botls directly to both motor ports:

Motor Flushing

  1. The manifold is designed with through “A” and “B” SAE Code 62 ports with grooves for O-Rings from both sides. Using gender changer plates (for example, solution from Inserta) the manifold can be mounted in any direction/position and ports can be easy swapped if it required.
  2. Anti-cavitation valve is integrated to pressure relief valve is a very compact cartridge, which saves space in the manifold. Like an example, here are solutions from Hydac (DBRV16P) and Rexroth (MHDBN).
  3. Flushing flow control valves examples: HYDAC (SR06-01 or SR08-01) or SUN Hydraulics FDCB-LAN. The benefit of Hydac SR valves is SAE ORB cavity: if you do not need flushing valve you can still use this universal manifold but jut plug cavity with the regular ORB port plug.
  4. And of course test ports. I like to involve as many test ports as it is possible to make easy maintenance.

The benefit of using flushing flow control valve (vs fixed orifice) is you can adjust required flow for any motor size specificly for application conditions, you do not need to pick the size and replace the orifice with each new motor.

The only thing you have to be careful about is a motor case drain pressure. Therefore, before adjusting a flow put a pressure gauge between the manifold and port “D1” and increase flow slowly to reach the required flow rate but not exceed max case pressure.

Flushing line from the manifold needs to be connected to the bottom case drain port of motor. From the top case drain port, the line needs to be plumbed directly to a tank.

Hydraulic cooler: suction or blowing air flow?

Just got an interesting response from Emmegi technical specialist about a choice between suction and blowing air flow of hydraulic coolers. The response is short but very deployed, so I would share it “as is”:

Here is our take on suction vs. blowing air flow:

  1. Blowing air flow: If you have seen a cooler that has been in the field for a while you will notice a clean doughnut shaped area where the air is blowing thru the cooler. In all four corners and in the center you will notice gunk/debris.

This indicates that the full surface area is not being utilized.

  1. Suction air flow: The fan creates a vacuum between the fan and cooling element. The air is very evenly distributed across the face of the cooler utilizing the full surface area.

On the downside, the fan blade is operating in less dense hot air, reducing the performance of the fan.

SUMMARY: For most hydraulic cooling applications the two effects cancel each other out and end up having nearly identical performance. The exception to this rule is for high temperature applications (oil temps above 175F).

  • For high temp applications the reduction of air density makes the blowing design more efficient.
  • The reason we supply standard coolers with suction air flow is that since the performance is typically the same, the suction air flow traps debris on the outside of the cooler where it is not only visible, but can be cleaned much easier.

if be honest, before this time I thought the suckers are more efficient coolers. Even to order cooler you need to specify symbol to make a blower (because the sucker is a standard).