Flow divider question 1

[Cnmmfg]

Iam trying to synchronize 3 cylinders for a press brake I was asked to design. Problem is they ordered a 4 port flow divider. Next problem is that I am having a real difficulty locating a 3 port divider(by the way this is a rotary gear divider). Is there a way to use the 4 port divider for just 3 cylinders by either plugging one port or running one port back to tank. Third idea is that this divider I have looks to be modular can I just unbolt the all thread that runs through it take out one section then bolt it back together for a 3 port modular. Any help would be appreciated as I am at a loss here.

Thanks
Chris

 

[MikeHalloran]

It probably is modular enough to remove one section.

If not, or if you don't want to affect the warranty, just connect the input and output of one section to each other and fill them with oil (using a bleed valve or similar).



Mike Halloran
Pembroke Pines, FL, USA

 

[IceStationZebra]

You could tie the fourth output back into the input. The only thing about that is will it create a pressure intensification? I'm too tired right now to reason it out.

ISZ

 

[Oldhydroman]

Nah... there won't be any pressure intensification because the redundant section will have the same pressure on its inlet and its outlet. So it won't be working as a motor and won't be "pumping up" the other three outlets. There will, however, be some parasitic losses through friction and churning.

DOL

 

[Jboggs]

Why do I always have to recommend this?

Call the manufacturer! Information from any other source is suspect.

 

[Oldhydroman]

Cheers Jboggs - it's nice to know that information from any source other than the manufacturer is suspect. I wonder if there is any point in this forum at all.

But, maybe there is a value in having a forum where a professional engineer can tap the brains of other professional engineers, particularly when looking for a source of information other than the manufacturer? Haven't you ever bought something and been completely unable to get any worthwhile advice from the manufacturer? You phone up but can't get past the know-nothing clerk who doesn't understand the question and is representing about a zillion different products. They can only promise to get back to you (at some unspecified date in the future) with price and delivery ... provided always that you can give the EXACT part number (including all spaces, dashes, slashes etc.). I could (but won't) name several hydraulic equipment suppliers whose products I will NOT use because their technical support is utterly appalling.

And, maybe there is a value in getting a second opinion from a bunch of professionals who have many decades of experience in their particular specialist fields. Hydraulic components can be installed in many different configurations and made to perform many different functions - some of which aren't in the manufacturer's [sometimes non-existant] application notes. Disabling one outlet of a rotary flow divider isn't particularly difficult as long as you know how to do it.

DOL

 

[Cnmmfg]

Thanks for the replies so far and yes the mfg is 0 help, I can't even get a return email from them so yes I am glad I stumbled across this forum were some real world knowledge is available as opposed to a one page tech sheet from the mfg. Getting back to the responses, it seems that one ports output could just be tee'ed back to the main input. The way this divider is plumbed is one imput is dived into four outputs, seems it would work just fine however will it be a problem when the flow is revered? I understand that these dividers work in both directions of flow ( synchronizing both directions of the cylinder stroke) I am just not sure if that plumbing will affect the reverse direction, seems that it won't but that's why I am here hydraulics aren't my strong suit.

Thanks
Chris

 

[MikeHalloran]

Tying one output back to a siamesed input should work okay.
Try to minimize the restrictions in that flow path.



Mike Halloran
Pembroke Pines, FL, USA

 

[Oldhydroman]

Hi Chris

Connecting one of your rotary flow divider outlets back to its common inlet will freewheel that section of the unit. The section doesn't "swallow" any net flow when running as a divider because its outlet is led back to the inlet. See if this helps:

Suppose you had 12 gpm coming from your DCV to the inlet of the flow divider - without any re-piping you would get four individual flows of 3 gpm each. But one of these flows is then led back to the inlet - so the divider inlet flow is now greater than the DCV flow, so each of the outlet flows is greater than one quarter of the DCV flow.

So let's call the flow from the DCV "q" gpm and the flow into the divider "Q" gpm. We know that each outlet will be Q/4 so the flow into the divider (Q) actually equals q+Q/4. From this equation [q+Q/4=Q] we can deduce that q=3Q/4 or, Q=4q/3. If the flow from the DCV (q) were 12 gpm then the actual flow into the flow divider inlet (Q) will be 16 gpm. The flow from each outlet will then be 4 gpm and this makes sense because one of these 4 gpm outlets will add to the 12 gpm from the DCV to give you the 16 gpm for the flow divider inlet.

Now when you run the thing in reverse (as a flow combiner) you will push 4 gpm into each of the three working "inlets" and they will turn the gears in such a way that the "unused" inlet will suck in 4 gpm. The combined outlet flow will be 16 gpm - of which 4 gpm will be sucked back into the redundant section - leaving 12 gpm to go back to the DCV. You do indeed have a three way flow divider.

BUT be very careful with your flow combining function, if one of your cylinders "hangs up" when the flow divider is running as a "combiner" then the flow from the remaining cylinders will just push the gears round anyway and the line from the stuck cylinder will cavitate (do you have any anti-cavitation valves in circuit?). If this happens you will loose synchronisation.

DOL

 

[kcj]

You could always remove the internal gears from that section, the idler gear on the smaller shaft, and leave the housing in place.
That would reduce the pumping losses very slightly, and reduce external plumbing.

 

[Jboggs]

Oldhydroman,
Points well taken. Please accept my apologies for any slights. They were not intended. I think you got my point, even if it was a little overstated.

The thing that just amazes me over and over again though is how many people never even think about contacting a manufacturer directly. And to my point - note that in his response to me Cnmmfg stated that the manufacturer didn't return his email. Believe me I understand the importance of customer support, and there is no excuse for not responding to customer requests, but if I have to have some information on an item, I'm not going to let an unanswered email stop me. I'm going to talk to a real person someway somehow, and if possible go up the chain as far as it takes to get the information I need.

Then I will remember the frustration of that exercise the next time I need a similar product, and seek a different source.

 

[Oldhydroman]

That's OK J, we're still good

You and me are in the same place - suppliers that want to reward their customers with the blank face of apathy (you know who you are) can look forward to a lack of future orders from those engineers that have been substantially hacked off. The converse is that those suppliers who provide professional, willing and helpful support; those are the people that get my loyalty.

Maybe we should start a "name them and shame them" thread - or would that be too controversial? On the other hand, I'd be more than happy to let slip a few names of companies whose technical representatives I hold in the highest regard.

Sorry Cnmmfg, I've gone of at a tangent. But I'm sure you'll remember how helpful this flow divider supplier was next time you need to buy one.

DOL

 

[kcj]

I think most engineers agree with above. Unfortunately, as is true in american consumer spending, the supplier that has support, information, startup assistance, loans out samples for review, etc has a a slightly higher cost. The engineers work up a decision, the parts released, and purchasing cuts the PO to another supplier, the blank face of apathy one, because the price is 3% cheaper and they get rewarded for const control........

not a new problem and I have no solutions other than deal with the best vendors I can and push to show their value added to us

 

[Oldhydroman]

"The bitterness of poor quality remains long after the sweetness of a low price is forgotten" - Benjamin Franklin.

This also applies to aftersales support. Having to spend time trying to get hold of someone to give the engineering support can completely cancel out the initial 3% cost saving. I don't know how to get round that problem either.

DOL

 

[som1973]

I agree that Synchronizing 3 cylinders is very difficult, but you need to use electronic feedback mechanism such as Electro-hydraulic proportional valve with linear feedback device (LVTD)mounted on the cylinder which accurately read the position of cylinder piston and give the feedback to the controller (PLC),which in turn gives feedback to the proportional valve to move by specific distance.

I know this is very expensive method.

 

[Cnmmfg]

Thanks for all the help, I think we will try to internally disable or if modular just remove one section. If we get it apart and that's not possible then we will try the plumbing method, rerouting the unused port back into the intake.

Thanks
Chris