Balance 16 Small Hyd Cylinders

What you want to do is commonly done, but if you require a great deal of accuracy, it is complicated and expensive.

Please answer the following to help us give you the correct guidance:

1. What is your tolerance? thousandths of an inch? a couple cm? etc.
2. Do all of your cylinders need to move in unison at the same rate/speed?
3. Are all of the cylinders under the same load? Or will one cylinder see more load than another?
4. What is your system pressure?
5. What is your load?
6. Do you have an existing hydraulic power unit you plan to use, or will a new HPU need to be designed/built?
7. Do you need feedback position on the cylinders?
8. What is the bore/stroke?
9. Do you already have the cylinders, or will they need to be purchased?

16 cylinders can be controlled in a variety of ways, some easier and cheaper than others, depending on the variables I have requested information about. If you need precision (tolerance of .001" for example) then you will need some $$$. Please answer the questions and I can give you appropriate advice on the matter.
Cheers,
-R

The air cylinder differences in length are approximatly 0.000/0.060. But I need to apply aproximatly 240 psi to each air cylinder to make the connection. The hyd cylinders do not need to move at the same rate as long as each air cylinder see approximatly 240 psi when they are engaged in the filling manifold. In other words I want to use the hyd cylinders to account for the difference of cylinder height while applying 240 psi to each cylinder.

I have not purchased any equipment at this time. Just brainstorming to understand the feasability and to develop the simplest way to do it.

Thanks for the reply!

Units, units, units! 0.000/0.060 what? Furlongs? Fathoms? Angstroms?

I would assume inches, since you use pressure units of psi, but to be sure...

If you need higher precision and accuracy than .060" you will need something other than hydraulics.

So what exactly are you moving and why?

Cant adjustable shims or something similar be placed on all the cylinders so that they all have the same maximum extended lengths?

This is for an automated production system. These are small air cyinders, similar to miniature scuba tanks. I want to fill 16 of them at a time. The differences in height is minimal but needs to be taken into consideration.

What if I cascaded the 16 hyd cylinders, the hyd cylinders would push the air cylinders into the manifold untill the hyd system sees 240 psi. Then hold the pressure while filling. Is there a way to do this?

Since you were discussing motion control, I (and a few others it appears) assumed "air cylinder" meant pneumatic actuator, not pressure vessel.

"What if I cascaded the 16 hyd cylinders, the hyd cylinders would push the air cylinders into the manifold untill the hyd system sees 240 psi. Then hold the pressure while filling. Is there a way to do this?"

Short answer, yes. There are standard sensors and valves that should meet your requirements. You will need to determine how quickly each step needs to function, and the repetition rate.

A few questions:

1. Is "240 psi" the pressure in the hydraulic circuit, or the force of the actuator against each air tank?
2. Will the air in the tanks be used for humans (e.g., air for breathing, or contact with food/water)?
3. What should happen if/when one of the hydraulic lines fails?
4. What should happen if/when an air tank (or any part of the pneumatic system) fails?
5. What should happen if/when there are fewer than 16 tanks to be filled?

My apologies... I'm dense at times...

But, I'm still having a hard time figuring out exactly what you are trying to do. These 16 Pneumatic cylinders are not Pneumatic actuators, but rather something more like an accumulator, or air tank? You are filling the tanks but need the inlet at the tank to be adjusted to align properly with the filling nozzle??

What work is being done by the hydraulic actuators?

It is possible to get .001 precision using hydraulics, but it's expensive, as I stated before.

Regulating pressure in the hydraulic system is easy. If the hydraulic actuators don't need to move at the same rate, or end up at the same location that also makes it easy. However, without a true understanding of what it is you are REALLY trying to accomplish I'm just shooting in the dark wasting time.

Do you have a schematic/drawing/sketch you can share?

Where are you in the world?

These are not pneumatic cylinders. We are filling air cylinders like a small (12 inches high) scuba tanks. I need to hold 16 of these up against a filling manifold. I want to locate them by hyd pressure. In other words, push the gang of 16 miniature scuba cylinders up into the manifold and hold them there with 240 psi from the hyd cylinders. If one scuba bottle is longer than the others the hyd cyinder will not travel as far as the other hyd cylinders and be limited by the hyd pressure in the system. The final location of the hyd cylinder is determined by the length of the small scuba tank and the limit of 240 psi hydrualic pressure. Once the entire hyd system sees 240 psi the hyd motor is stopped/regulated and the pressure held in the system at 240.

Yeah, Ok, now we are on the same page.

That's fairly easy to do.

Just out of curiosity, where do you get your 240psi figure from? Different bore/rod cylinders will exert different forces on the rod end at the same system pressure.

IE: a 2" bore cylinder will apply X amount of force at 240psi, while a 4" bore cylinder will apply (for example purposes) twice that much force. I believe it's the force needed to hold the bottles in place which you need to identify, and that (depending on cylinders chosen) will call out your needed system pressure. Always work from the load back to the pump/motor, accounting for pressure drops and system losses along the way.

You need a Hydraulic Power Unit to provide the pressure/flow. I would use a compensated piston pump (saves energy while system is not in use, VS a fixed displacement pump) to provide the proper flow/pressure to the system, and plumb all the cylinders in parallel. Set the compensator higher than the system relief valve by a decent measure (see the literature). Set the Relief Valve to your "240Psi", make sure you have calculated the flow needed to run this system at the speeds you wish.

It's fairly straightforward application, and should not end up costing you all that much in comparison to some things. At that low of pressures the equipment can be purchased for quite a bit less than say a system running at 4300psi.

So the bottom line is, yes, you have chosen a great technology (hydraulics) to do what you want.

Do you have shop air accessible?

-just a thought-

If you run the system using Pneumatics you can get by for even cheaper with less environmental hazards and costs. but there are always trade-offs, but from the sounds of it, you just need this to "jam" the bottles into the manifold and hold it there for "X" period of time... correct?

What is the force needed to do the job?

If you are in the western US send me a PM and I can help you design the system, and quote you out on the job. I work for a Hydraulics/Pneumatics distributor out of Oregon, and would be happy to help.

For what I've seen in the past using pneumatics in test jigs. If all your individual hydraulic cylinders share a common manifold to supply them. The slight height difference of the air tanks should not be a problem as long as the air filling manifold does not move.

The slight difference in air tanks mean the hydraulic cylinder would extend a little more or less. The stroke range of the cylinder would need to allow for variations but not to "top out" before air tanks are in place. Once the hydraulic cylinder makes contact with the air tank and pushes it into place and movement stops is when the pressure builds.

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If you have access to compressed air already, have you thought about using pneumatic cylinders instead. There would be the savings of not having to use hydraulic parts. Its cleaner if there a problem, less of fire potential around compress air systems_{(if that your filling use)}, for the coupling pressure, pneumatics are capable, speed is adjustable. Filling positions could be isolated with valves if filling less that 16 cylinders._{(same for hydraulic)}.

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Regardless of the system you design or use think of safety to keep someone from getting "pinched" by the system closing. By using two hands switches or guards that block hand/body access when closing.

Thank you everyone for your thoughtful replies! Jess

Spring bottom sockets or rubber hockey puck type buffer account nicely for slight height variations. Do not mar the surface either. Tornado's solution is the simplest.

Yes, this would work just fine, albeit with a lot of cylinders and connections. Such an arrangement guarantees that the force applied to each tank is the same, provided, of course, that the hydraulic cylinders are not allowed to fully extend. It also could allow for future modifications in tank length (and mixes of old and new tanks).

A beam operated by a single cylinder could work well, and would be hydraulically simpler. However, if the beam is rigidly mounted to the cylinder rod, then different tank lengths put a (possibly slight) bending load on the cylinder rod. The beam could be supported on linear bearings suitably spaced (so that it remains always perpendicular to the direction of travel), but such an arrangement gets bulky and expensive. The force applied to each tank would be in a range determined by the beam flex and the individual compressions of the compensating springs or pads. It is quite possible that the simple beam fixed to the cylinder rod would work just fine, given some springs or elastomeric pads at each tank location. Perhaps mounting the beam semi-rigidly would help, so it could tilt a degree or so either side of center.

You would want to evaluate the possibility that one tank would jam before being seated. With a beam, none of the cylinders would seat, in this case. But a single prox switch in a single cylinder and beam arrangement would detect this, whereas it could take 16 prox switches to detect any single tank not being seated with individual cylinders.