Hydraulic to pneumatic comparisson

[monkeymark]

After looking at the thread about pipe benders I noticed it needed a ram with decent travel.
At some point I'm going to make one and it got me thinking.

I'd prefer pneumatic but there's not many rams available with a long enough stroke.

A little research has informed me a hydro cylinder can be used with air.

But, how does this affect output force? I believe force it worked out by bore and pressure.
Hydro fluid by nature doesn't compress where as air obviously does. Would the cylinder work the same once the air in the cylinder has compressed?

 

[wyn]

Using a hydraulic ram with air is a waste of time as you will still only have around 100-150psi with air compared to 2-3000psi with oil

Would the cylinder work the same once the air in the cylinder has compressed?

It might do but you would have to compress the air to the same pressure as the oil....2-3000 psi.


You could use something like this....i use one with a 10 ton cylinder for various things and it's quite handy.

 

[rtbcomp]

A ram ultimately delivers force, so to get the same force from air at 100 psi as you would from liquid at 3000 psi the piston area in the pneumatic cylinder will have to be 3000/100 = 30 times that of the hydraulic cylinder.

 

[outofthefire]

I've got a hare pneumatic press that I use like power hammer and even though its fairly slow I wouldn't say its controllable like a hydraulic ram would be.

 

[monkeymark]

Ah I see. I was hoping to avoid the mess that can be associated with it.

It may well still provide enough power perhaps.

 

[monkeymark]

I cant seem to find a decent size pneumatic cylinder without going to silly prices.
May try and get a cheapo hydraulic and see what happens.

 

[Maker]

A hydraulic cylinder will work fine with air but like rtbcomp said, it will have about 1/30th of the power. The problem with using something compressible it it will always try to fully extend the cylinder so if your bending something small enough for air to be powerful enough it will almost certainly over bend it. You could probably get around this problem by having a stop secured to stop it going too far. A hydraulic system will be much better because you get power and control. If you can't afford/don't want an electric pump unit you could get a hand one like this.

 

[monkeymark]

One project I'm currently thinking of is a pnuematic briquete maker.
Pneumatic simply because it means my kids can do it with me without struggling.

The rams I currently have are too small. Largest is a 40mm bore. At 100psi that should give about 80kg. Not as much as I'd like.
I could utilise leverage but then a longer stroke would be needed.

 

[Maker]

One project I'm currently thinking of is a pnuematic briquete maker.
Pneumatic simply because it means my kids can do it with me without struggling.

The rams I currently have are too small. Largest is a 40mm bore. At 100psi that should give about 80kg. Not as much as I'd like.
I could utilise leverage but then a longer stroke would be needed.

Instead of a larger cylinder bore you could use a smaller pellet forming tube to apply more pressure to the actual pellets.

 

[the snooper]

Instead of a larger cylinder bore you could use a smaller pellet forming tube to apply more pressure to the actual pellets.

he's making briquettes not pellets

 

[Maker]

he's making briquettes not pellets

Ok, make smaller briquettes.

 

[the snooper]

Ok, make smaller briquettes.

or pellets

 

[Rig Pig]

Screw and air motor?

 

[dannyp]

your not going to squeeze much with a pnumatic cylinder unless it's massive.

how much force are you looking for and how fast ?

 

[Maker]

Oh yeah, I forgot about that, the bigger the bore, the slower it will move.

 

[monkeymark]

Not too bothered about speed.The best manual one ive seen presses with roughly 3/4 ton pressure.

 

[Wendelspanswick]

What about an air over hydraulic cylinder?
Scrub that, just checked prices!

 

[monkeymark]

Looks like hydraulic then.
I want it to be fairly portable so thinking a pump from something like a forklift or convertible power hood?

 

[Rig Pig]

There's a big difference between a convertible roof pump and a forklift pump! A car power steering pump and a lawnmower engine may make a useful & cheap power pack.

 

[monkeymark]

There's a big difference between a convertible roof pump and a forklift pump! A car power steering pump and a lawnmower engine may make a useful & cheap power pack.

I know little about hydraulics. I thought a convertible pump would be too small. A forklift pump just as i saw one on fleabay.
Did consider an electric power steering pump too as at least in negates the need for a separate motor. Again, not sure on suitability though.