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Multiple Hydraulic cylinder synchronization

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blacktj00

Mechanical
Feb 28, 2007
2
Hello, We have an application for a material transfer device that uses 17 arms to transfer a 6000lb, 200ft long pole into a piece of equipment. The pole can also have some water in it that gives a few hundred more lbs that can be distributed most anywhere along the 200 ft. The arms would need to stay within 1/4" of each other on the down stroke (with gravity). The cylinders would be full stroked each time. (right now I am looking at 2in bore x 36in stroke)

If we used a hydraulic system would it be possible to achieve this synchronization with gear flow dividers, or would we have to go the route of electrohydraulics, with indivudual feed back loops on each actuator. If gear flow dividers would work, can I feed them into each other, e.g. a 1 to 4 that feed 4 x 1 to 4's to get 16? (I know one short, not sure how to handle that odd one)

Also I read some posts on running cylinders in series but not sure if you could do that with 17!?!?

Thanks
 
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Lots of Luck with any type Flow Divider to consistently maintain 1/4' in 36". Possibly +/- 1/2" with resynchronizaion at both ends.

The Electro-Mechanical way will work for sure. Not cheap though.

Another expensive way is to use Tandem Cylinders with the Doule Rod End Cylinders cross ported so they have to move together and can transfer energy with your uneven load.

Also could be Single Rod Cylinders as Force and Double Rod Slave Cylinders as synchronization to keep overall cylinder length less.

As for the odd cylinder with Flow Dividers, put it in the middle and pipe it directly to the Directional Control Valves "A" and "B" ports. With this arrangement it would be giving force but could not force the other cylinders out of synch.

Cylinders in series works also but need to be Double Rod or odd-ball Singe Rod Specials where the rod end flow of one cylinder matched the cap end flow of the next cylinder and so on through the 17 cylinders. The Odd-ball single rod circuits are usually in a two cylinder arrangement, Pacific Press press brakes for one.

In any case a series circuit requires all cylinders in the series to be capable of moving the total load individully. This is because you are splitting the load and input pressure over the 17 cylinders.

I have a circuits book that includes 10 ways to synchronize actuators. You can see a spot about it on my web site The book also has many other Hydraulic and Pneumatic circuits with explanations of how they work and the possible problems that can be encountered in the different ways of applying Fluid Power components.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING, INC.
 
Thanks for the info, I thought that was going to be the answer to flow dividers.

So if we went with the cylinders in series, (double rod configuration) how do you fill the system/maintain? Do I need a normally closed valve between ports on each cylinder that could be opened to fill?

Also I was on the Dynex website ( They have a split flow pump where each piston is directed to an outlet. They claim a much more precise flow than a divider. Any expierence with these?

Thanks again
 
As you have determined it is not an easy thing to fill the cylinders in the series, keep them full plus have a way to resynchronize them when seals start bypassing. I cover the resynchronizing in the synchronizing section on the Fluid Power Circuits Explained book. The original filling and refilling is another problem with this design. The two circuits I was involved with were filled with the cylinders prefied manually, disconnected from the work and cycled in the air until they were free of trapped air.

I have only seen one circuit using the Dynex pump design, was an Enerpac I think, raising a large reservoir, 5,000 Gallons, 15' to clear an area to work in. However it took about 3 hours to get it up.

This type circuits main disadvantage in my opinion is the fact that the cylinders will raise in increments and never be in phase.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING, INC.
 
Look at a control logix PLC and get 9 M02AS or HYD02 cards. Synchronizing 17 axes will be easy.

 
When I worked on agricultural equipment we would use a small orifice that bled oil across the piston seal when the cylinder was fully extended (could also be retracted). It allows your cylinders to rephase and allows for the initial fill. Just hold the circuit in extend mode - the oil will slowly go thru the orifice into the next cylinder (we had 3 in series). The bad thing was that the cylinders would not hold at full stroke unless enough oil was supplied to make up for the loss through the rephasing orifices. We didn't, so the machine would raise to full height and when the valve was returned to neutral the machine would sag an inch or two.

See picture 3 in this article.

ISZ
 
Dear Friends

Has anybody thought of pressure intensification, in case we use double rod cylinders in series to achieve our synchronization purpose. We can achieve our purpose but at the cost of pressure instensification. This pressure intensification will be the highest in the first cylinder & less to respective cylinders depending their order. More cylinders, more pressure intensification. Don't you think, it will increase cost of components like thick wall cylinders, thick wall pipes, high pressure pumps, hoses & other comparatively higher pressure rated components. Pl let me know your comments.

Best Regards
Rajan Bedi
 
The highest possible pressure in the series of cylinders will be at the inlet to the first one in the series. From that point on, pressure decreases until the last cyliders return to tank at no pressure.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
 
I can't believe the extremes people will go to avoid using electronic controls to synchronize hydraulic cylinders. Budt, you have seen this done and yet you still resist. You get 17 valves, all the same. You get 17 cylinders, all the same. You get 17 MDT rods, all the same. You get the PLC and 9 M02AS controllers, all the same. Spares are easy then because one can use standard parts. Try to get a quantity discount. :) There will be no pressure intensification or drooping of the last few cylinders in the chain. It could have, should have been done by now.




 
Peter wrote:

"Budt, you have seen this done and yet you still resist."

I did'nt want to appear to be resisting just realstic. It is more expensive to use Proportional valve, Feedback Transducers and all the electronics but is necessary on some applications.

On the system you are referring to, if you remember, I came to you first or you would not have known it existed.

I,m getting smarter in my waning years.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
 
How about one cylinder driving a system of crank arms? Or is there a need for independent elevation control at each pick point?
 
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