Pneumatics vs. Hydraulics

[Ljohnsaw]

My mill build is designed around an electric motor to drive the band.  I've read a lot of neat add-ons with hydraulics (log turners, clamps, leveling, etc.).  I was wondering if there is any merit in using pneumatic rams.  It would be a whole lot easier to plumb (flexible, lightweight tubing).  I think, with the right linkage, a clamp would be equivalent to hydraulic since I don't see the need for "tons" of clamping pressure - how about a log turner - need too much power??

I could see that a pneumatic ram would want to overshoot when rolling a log where hydraulic would stop the minute you move the control lever to neutral.  Anyone tried air?

[Don_Papenburg]

air works  It tends to move faster than oil .  You need larger dia cylinders to get the holding power because of the pressure diff. pneumatic cylinders tend to be higher priced .  Might be that they are used in factories more than in the public .

[ladylake]

I'd sure go with hydraulics, I think air would be hard to control thing like the log stops, toe boards, chain turner plus you would need huge cylinders.   Steve

[hackberry jake]

Air would be more dangerous. If pressure built up and then something broke loose, it would throw whatever it was pushing on. Air is too springy.

[Bill Gaiche]

Air can be good in lots of areas, but where you need to control things and for the shear power hydraulics is by far the best. Air compresses and can make for jerky cylinders without some type of regulator on both sides. bg

[wetdog]

Air works great. I once worked at a plywood facility and we used hundreds of cylinders throughout the plant. The biggest issue is the amount of air used. It will take a very large compressor or one very large volume tank.

[stavebuyer]

Air works great for low pressure applications, where hundreds of pounds of pressure can get the job done versus thousands of pounds for the slower hydraulics. Kickers, stops etc. work great with air cylinders. Another consideration is climate. Air can be a nightmare to keep operating in sub-freezing temperatures. Even with driers and anti-freeze, air lines can be a real chore to keep from freezing.

[Ljohnsaw]

Wow, thanks all for your comments. 

Yes, air is springy.  I'm thinking for raising and lowering the log stops it would work good,maybe even great.  For raising a toe board, maybe not so good but I could raise a log and slip some shims in way easier than cranking up a jack and then drop it back down.  Might even work as a log turner.  I like to experiment - you should see my aquaponics set up now, Mr. Goldberg would be proud! :D

[coastlogger]

Good old Rube,an inspiration to us all.

[justallan1]

I think the biggest issue with using air is you have pre-set distances where everything is all or none. You can't just go half of that distance and stop unless you also install either electric or air powered stops, which is a whole new can of worms.

Allan

[bandmiller2]

Air would be fine for such things as kickers, air motors est. but it lacks power and control, movement is sudden and uncontrollable. Frank C.

[slider]

I watched a video of a big production mill running a while back a[Jackson],I think but it would flip a cant so fast it had to be air moving those cylinders.

[Ron Wenrich]

I ran 2 Jackson mills.  They were hydraulic cylinders, and you can flip cants quickly when you have a good technique.

I also ran a couple of air mills, and their downturns were poor.  They lacked the power needed to flip the log.  I don't recall of any log turners that were air powered. 

[backwoods sawyer]

We ran three 200hp air compresors in the production mill. It was used thru out the plant for stops, board kickers, drop tables and pans, hold down rolls, positioning arms, the sorter was a big air user as air is fast. The only turner-drop out that used air to flip a cant was on the down slope following an unscrambler so the cant would already be at a 45* and a 4x30x10' cant would allmost stall it out and then it would throw the cant on down the chain as it built enough presure to flipped it. As far as handling and turning logs and heavy cants it was all hydraulic.

[Dave Shepard]

That's a lot of air. I used to run the air compressors for snow making years ago. When everything was up and running we used 14,600 cfm@90 psi.

[whitepine2]

   You cannot compress liquid it it positive air can be compressed and heat can
change settings not so much with liquid. There could be a use for air but hydraulic will stay if running right air if you would like to lift something and if some movement would not effect the operation but why bother use liquidb and be done with it.   

[hackberry jake]

You have to be careful saying liquid doesn't compress. My brother is a mechanical engineer and we had this discussion once. Liquid does compress, just takes a lot more force than a gas.

[Gary_C]

For all practical purposes, liquids are considered incompressible.

But yes, in theory liquids are compressible, but it takes very high pressures and even then, not so much.

[hackberry jake]

For all practical purposes, liquids are considered incompressible.

But yes, in theory liquids are compressible, but it takes very high pressures and even then, not so much.

agreed

[backwoods sawyer]

I tested the theiry today while putting the truck motor back together. Liquids in the cylindar does not compress, must pull plugs to remove liquids  :

[jamesamd]

I do not have a sawmill but I know pneumatics has no practical use for heavy clamping or precisely controled  positioning.
However it works great for blowing sawdust of of everything  :

Jim

[longtime lurker]

Air works, particularly in a fixed mill. Our resaws and docking saws are all pneumatic and it's great - one of the overlooked points so far is that burst and/or leaking pipes and fittings are mess free.
But we use hydraulics on the log infeed and handling side: hydraulics have more power for a given installation size. It's not that air wouldn't work, it's that a compressor big enough to provide the necessary volumes is impractical. We run a 45 cfm with outsize receivers to have a large volume held on demand, no way is that enough to run turners as well, and no way would it be classed as portable.