pneumatic cylinder question

Hello All,
I have a pneumatics question for the group; I need the behavior of a single-acting cylinder with spring return, but I need more force than the spring return can provide.

I'm thinking of creating a "spring" by plumbing the rod-end port of a double-acting cylinder to a sealed and pressurized (with air) reservoir to act as the return spring. I would fine-tune the return pressure by adjusting the air in the reservoir. I realize I will need to periodically check the pressure and provide a means of introducing makeup air - probably a Schrader valve - to account for losses around the cylinder's seal, but that's totally do-able.

The cylinders involved are small - 3/4" bore and 6" stroke, so the reservoir can probably be little larger than a pop can. It's a long story, but suffice to say I can only run one air line to each location. Control will be handled by 2-way, 3-port solenoids, mounted remotely.

Thoughts?


Thanks,

-rpoet

Seems like a lot of extra work. Just put a small regulator on each side of the cylinder. Set one low pressure for return stroke and one high pressure for the extend stroke.
Your gonna need a 5 port 3 way valve the 2 way 3 port won't work as you won't have a vent for your cylinder. If you let it in you gotta let it out.

I've attached a PDF, as I don't think I explained what I'm thinking of doing very well. I hope the picture helps clarify.

-rpoet

Your plan will certainly work, at least for short periods of time. Keeping the "spring" side sealed will be a challenge.

Have you considered adding a gas spring to aid in the retract?

Keith

Looks good on paper. Should work pretty well. You'll probably need some kind of constant make for the ballast side though. Even a high quallity cylinder will weep from the rod seals and depending on the cyclical rate of the cylinder I think a mist lube might be in order.

If you don't need all the force on the extend, you can use a cylinder without a spring and plumb the retract side to the air supply all the time. When extending you will have a reduced force (basically the area of the rod times the pressure) but when retracting, you will have full force of the annular area times the pressure. Of course if you can't live with the lower force on the extend then this will not work.

We use this solution very often.

Your plan will work if the piston seal is perfect and never leaks a single molecule, and if you can afford the increasing extra load during the extend stroke. When you find a cylinder that perfect, please let me know. I have never seen one.

Norman (ndzied1) has a good idea, but that requires a rod end air line.

Why can you not run two 1/4 air lines and keep it simple? (4 or 5 way valve, single solenoid)

I'm sure there's a good reason, which leads to Keiths suggestion. external mechanical retraction via gas charged cylinder...

From the original post:

Originally posted by rpoet:

It's a long story, but suffice to say I can only run one air line to each location.

Click to expand...

No matter where you locate the pilot operated valve you would still need to get two lines out to the cylinder.

Have you thought of using a vacuum generator?

Keith

kamenges said:

Have you thought of using a vacuum generator?

Click to expand...

Hey that's a good solution...just make sure your valves have external pilot and can handle a vacuum. Then you blow the piston out, and suck it back with one air line.

rpoet said:

but suffice to say I can only run one air line to each location.

-rpoet

Click to expand...

Presuming that only one airline is possible for each location. Mount the pressure reducing regulator and the check valve at the cylinder. This will keep the accumulator charged when ever the piston is cycled. A bubble tight check valve will be needed.

OkiePC said:

Your plan will work if the piston seal is perfect and never leaks a single molecule, and if you can afford the increasing extra load during the extend stroke. When you find a cylinder that perfect, please let me know. I have never seen one.

Norman (ndzied1) has a good idea, but that requires a rod end air line.

Why can you not run two 1/4 air lines and keep it simple? (4 or 5 way valve, single solenoid)

I'm sure there's a good reason, which leads to Keiths suggestion. external mechanical retraction via gas charged cylinder...

Click to expand...

Like I said: We use this solution very often and works fine.
We use normal Festo and SMC cylinders.

nonuke said:

Like I said: We use this solution very often and works fine.
We use normal Festo and SMC cylinders.

Click to expand...

I was referring to the OP idea of using an accumulator on the rod end, your method with the shuttle valve looks fine.

If there is room (or budget or whatever) for an accumulator and assoicated plumbing then surely there is room for another air line. Just use a double acting cylinder - its simple, trouble free, easy to maintain, easy to understand, and headache free.

Well, rpoet, it may be time to cough up why you can't run two air lines to your cylinder or you thread will be replete with double acting cylinder/4-5 way valve solutions. It does seem to be a reasonable question why you can't run what would likly amount to a 1/16" nylon tube out to the cylinder.

Keith