pneumatic press?

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I just picked up a few air cylinders from a guy for a very good price.  I needed one for a project I have been working on and ended up buying 4 of them since he was getting rid of them for fairly cheap.  They are nice made in the USA Parker air cylinders.  One is 6" bore by 6" stroke and another is 5" bore by 11" stroke.  I got to thinking that the 6" one might make a good press.  I don't have a press right now and have been wanting to make one for a while now.  Does anyone have a pneumatic air press?  The 6" cylinder would have 4200 pounds of force at 150 PSI, not as much as a 10 ton press but would think that would be good for most things around the shop.   I know a bottle jack would be more powerful but thought this might be powerful enough to have around the shop.  And thought I might get more control with the right valving.  The cylinder says it can go up to 250 PSI but my compressor only goes to 175.Has anyone used a pneumatic press and how are they compared to one with a bottle jack?  I googled them and they are crazy expensive for just a 1000 pounds force one from grainger is almost 3000 dollars.  I didn't really need these cylinders but paid very little for them so was trying to think of some projects to use them for.  So open for other ideas if the press idea turns out to be a bad one.
Reply:Ponch,As gasses (such as air) are compressible, you'd have a hard time with a air powered press as you get two positions with an air cyinder: extended and retracted.Example: You are pressing a bearing out of a housing of some kind, and the bearing is quite stubborn and requires a fair amount of force.  You keep jacking the air pressure up until you have sufficent force to break the bearing free and KA-POW! The bearing breaks free, allowing the cylinder to fully extend very quickly, launching the bearing at a high rate of speed into your foot positioned directly below the press.In this same example with a hydraulic press, hydraulic fluid is, for all intensive purposes, incompressible.  You have to keep adding fluid to make the cylider move, so you get a nice, slow, movement of the bearing out of the housing, even after its broken free.  It still drops onto your foot, but it doesn't get launched.As for ideas for your air cylinders, I think a catapult would be excellent.  Practical? not so much... but you could experement with that whole expanding gasses theory.If it doesn't fit, you aren't hitting it hard enough!Miller AerowaveMiller Radiator 1A4.5" DeWalt (with the paddle switch!)Jackson NexGen Helmet
Reply:Originally Posted by GT StevePonch,As gasses (such as air) are compressible, you'd have a hard time with a air powered press as you get two positions with an air cyinder: extended and retracted.Example: You are pressing a bearing out of a housing of some kind, and the bearing is quite stubborn and requires a fair amount of force.  You keep jacking the air pressure up until you have sufficent force to break the bearing free and KA-POW! The bearing breaks free, allowing the cylinder to fully extend very quickly, launching the bearing at a high rate of speed into your foot positioned directly below the press.In this same example with a hydraulic press, hydraulic fluid is, for all intensive purposes, incompressible.  You have to keep adding fluid to make the cylider move, so you get a nice, slow, movement of the bearing out of the housing, even after its broken free.  It still drops onto your foot, but it doesn't get launched.As for ideas for your air cylinders, I think a catapult would be excellent.  Practical? not so much... but you could experement with that whole expanding gasses theory.
Reply:Pop can crusher.  The one with a 6" stroke would be perfect for a single can.My name's not Jim....
Reply:I may be way off on this one but I will toss out my idea for your consideration.Are these are cylinders single action or double action?  Meaning can air be applied to extend the cylinder as well as contract the cylinder?  GT Steve has a very good point as far as once there is not resistance on the cylinder it will slam to its fully extended position.  However they make a valve, called a flow control valve which should be able to counteract this.How a flow control valve works is that in one direction air/fluid is unrestricted, and in the other direction in can be adjusted to be very slow.  What you would want to do is have your compressor hooked up to the port on the cylinder which extends it.  You then attach this valve to the exhaust port on the cylinder.So now lets take the example Steve gave of pushing a bearing out of a housing.  You crank up your PSI on the inlet of the cylinder to start to push out the bearing.  Once its free the cylinder will want to push all of the way to full extension, once it start to travel quickly it will create a lot of air coming out of the exhaust port.  However, because of the back pressure created by the valve on the exhaust only allowing say .01cfm to flow through it.... Once the bearing is free the resistance that the valve creates on the exhaust side of the cylinder it should slow down the travel speed on the cylinder so that it does not slam the bearing into your foot.I have used one of these valves on a dual action cylinder and it worked quite well.  These are also used a lot on props which take advantage of air cylinders/pneumatics to move things in a haunted house etc. However I have never used one of these on something that has a ton of pressure on it... we were only running 15-50psi.  But the valve is supposed to be able to take up to 2000 psi and still meter the flow.Here is a link to what I am talking about.  Hope this helps.  If you want to try it, I say buy one for Grainger and test it out to see if it works, if it doesnt slow the cylinder enough return it and get your money back and use the cylinders for something else.http://www.grainger.com/Grainger/COL...853?Pid=search
Reply:GT Steve-How about an air-over-oil system with flow controls on the oil lines to the cylinder?He could use the same cylinder and just make  air/oil chambers to pressurize the oil.Last edited by jpump5; 08-17-2010 at 06:39 AM.Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:They are double acting cylinders.  I have used the adjustable valves before and they do work nice but not sure if they would be right in this situation.  Might have to try some out and see.Can you use a pneumatic air cylinder as a hydraulic fluid cylinder?  If I buy a hydraulic pump and plumb some hoses to the pneumatic cylinder will it work?  I thought about this also but didn't know if the seals on the air cylinders could handle the hydraulic fluid.  Also the cylinders says 250 PSI envolope(not exactly sure what "envolope" means but would think that would be the max pressure), and I believe the hydraulic pumps put out several thousand PSI to get their massive power so that probably wouldn't work?  If I could use these cylinders for hydraulic rams I will start looking for a hydraulic pump of some kind and start building a press.  If not then I guess I will have to wait and look for true hydraulic setup or just buy a HF bottle jack.  The 6" would make a nice can crusher but think with over 2 tons of power it would be a little over kill!  This thing is huge and weighs a lot.
Reply:Have you seen the air powered bumper jacks?Used to be one in every sevice station across the country,then hyd.floor jacks took over.Air cylinders work great when moving something that is free to move but they are an explosion waiting to happen when trying to move something that is stuck.Look up a "cryderman shaft mucker".Its a swinging and telescoping clamshell mucker,as tall as fifty feet.Its air powered with ten foot rams and takes REAL skill to operate,the youngsters get a lot of watching and a small amount of hands on time until they can operate without smashing everything in the bottom of the shaft.Try putting an oscillating valve on it and make a pogo stick soil tamper.How about a basket full of corn tied on the end for a squirrel launcher?Screen door closer for the mother in law?tractor,loader.dozer,backhoe,and all the tools to keep em movin