Closed center flow divider

[Harry in Ky]

I'm currently in the process of setting up a hydraulic power unit, consisting of an engine driven closed center pressure compensated piston pump. When I got the unit it was my understanding it would be rated at 17 - 18 GPM. I am planning to use it to run a hydraulic motor rated for +- 19 GPM. Now I finally have the thing actually running, and am in the process of checking things out, it seems to be closer to 25 GPM at moderate RPM. More than I planned for, and don't want to simply slow the engine down to reduce the flow. For a number of reasons.

I also have another hydraulic motor I need to power that needs about 7 GPM to operate at the speed we want. I'd planned to run it with a separate pump, keeping the two systems separated, but with the flow I have here, I'm thinking I can run both motors with the one pump and disregard the other idea. I believe it will have enough flow, just not sure how to separate it. I think if I can split off the 7 GPM, what's left will run the big motor at about the RPM we want.

I was told that this type flow control could be used with closed center systems, and can divide the flow with both ports pressurized without a problem. I've seen and used a number of them over the years but not on closed center. Only open center.

Has anyone seen this type used that way?

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[oldnslo]

Harry
Most priority flow controls stop or block all flow if the priority leg flow is blocked or stopped. I did not see a schematic for that flow control.

Do you need one portion of the circuit to have priority over the others?

How precise and consistent do you need the flow to be to each circuit? If not super accurate over varying loads you can use simple needle valve to feed each circuit. If greater precision is required then pressure compensated flow control could be used.

 

[Harry in Ky]

I'm not dedicated to that particular item. Simply wondering about that style of unit. I don't need (or want) one with a relief, and have seen any number of them listed from many sources. Assuming the basics of operation are pretty much the same with all of them. I've never seen one used with closed center before, but I don't see why it wouldn't work. I've always used them open center and sent the exhaust flow back to sump. The literature says it can be used to power another circuit, so I'm wondering if anyone has ever seen or done that?

Precise and consistent are relative terms here. I'm powering two separate motors, both will operate at the same time, starting and stopping together. Not sure what the pressure differences might be between them under load just yet. It seems to me that this would be a simple and inexpensive solution based on what I see. I think I'm going to try it unless I get some seriously negative feedback.

Also, I see it mentioned that exhaust flow is pressure compensated. I'm not sure just what that means.

 

[LouNY]

Flow dividers will work on a closed center system.
Myself I prefer the rotary flow dividers but they are not adjustable.
I see in your first post that you are getting more flow then anticipated from your pump.
Is that with no back pressure on the flow loop.

 

[Harry in Ky]

No. That's running the pump output through a Hedland 30 GPM flow meter and jacked up to 2000 PSI.

 

[oldnslo]

Rotary or gear type flow dividers work well but they must have provisions to never block flow in one circuit while the other is still flowing since the they will also act as pressure intensifiers. The reason for this is the open flow path now acts like a motor while the blocked side turns into a pump.

The reason you usually do not see priority flow controls in closed loop system is that the pump is variable volume and only provides flow required. The priority flow control will allow excess pump flow back to tank creating heat and wasting energy.