I have a Pneumatic cylinder I bought a few weeks ago and I am planning to use it as a log splitter. It has a 6" bore with a 16" stroke @ Max PSI of 250.
My question is how can I get more PSI to the cylinder if my home air compressor has a setting of 120 psi? Is there some sort of way that I can increase the PSI through a pressure valve or can I use a 2nd tank that holds a higher PSI?
I have already purchased all the line and connectors. I went with a 3/8" ID hard plastic line. max 300 psi control valve and a pneumatic hand lever.
I’ll start off with the caveat that my experience with pneumatics is limited, so take my advice with a grain of salt.
An air amplifier (essentially a pneumatically powered air compressor) may be one option to look in to. I can’t comment on how practical it will be for your application since I’ve only dealt with them from a maintenance perspective. My guess is that it may end up not making sense financially, depending on how it compares in cost to buying the right compressor.
I also have to ask for my own knowledge, are you at all concerned about sudden energy releases/shock loading when a stubborn log finally splits due to the compressibility of of the air in the cylinder?
I’d go farther than what Stick said, viz., what you are proposing [1] is extremely dangerous, [2] will be exceeding wasteful of energy, , and [3] will be very slow.
I’d recommend seeing if you can return your pneumatic components unused and credit their value toward purchasing hydraulic components instead; far safer due to the virtual incompressibility of liquids, less energy wasted in needless air compression, and faster splitting operations.
Others are free to disagree…but I don’t think I’m wrong.
I have been watching some youtube videos on some pneumatic splitters. From what I have seen thus far once log finally does split the energy goes into the wood flying away from the splitter violently or the cylinder stops. Now the energy inside the cylinder when it stops I am not sure if that going to be a big deal or not. with the lever controlling air in an out of the cylinder.
I know Hydraulic is much easier and has a higher tonnage and makes the process easier, but this more affordable than hydraulic and and its just a fun project. I try to build stuff within a small budget out of all kinds of misc items. Just like my grills out of 55 gallon barrels or wind chimes out of transmission parts, washers, and fishing line braid.
Crshears, you’re definitely right, I maybe should have been more blunt, but not being familiar with log splitters I held back a bit. I’d also add a fourth concern that this thing will likely beat itself to pieces from parts slamming into each other every time a lot of energy is released (whether it’s the internal stops in the cylinder or an external stop somewhere depends on the design).
And sbaugh, just because it’s a fun project doesn’t make you immune to a piece of “wood flying away from the splitter violently” and hitting you (probably somewhere along the femoral artery based on the height of typical log splitters).
@crshears is 100% correct. Look around at all the commercial log splitters. Hydraulic! Not a single pneumatic one I could find. The main reason is safety. Your safety.
My advice, let’s be safe out there, go hydraulic.
One problem I see is the huge volume of gas that must be displaced to do the work or take the pressure off. Huge volumes require long movements. With a hydraulic oil, it’s like 1 cc or a big droplet. Small movements, so “harm’s way” is easy to avoid.
There are two issues.
One is the action of a pneumatic cylinder versus a hydraulic cylinder when the opposition to movement is removed.
The hydraulic cylinder continues to move slowly.
The air cylinder goes full stroke rapidly.
Two. Your force is off by an order of magnitude.
Your 6" air cylinderwith 120 PSIG will exert a force of about 3400 lbs.
A 4 inch or 6 inch hydraulic log splitter at 1500 PSIG to 2000 PSIG to exert a pressure of about 41,000 lbs to 55,000 lbs.
Why do commercial splitters use 4" or 6" hydraulic cylinders?
Is there something they know about splitting logs that we don’t know?
There is a third issue.
You will certainly increase the air pressure to get more force.
Somewhere around 300 psi, given the (inevitable) presence of a drop or two of lubricating oil,
the cylinder will someday become confused about whether it’s
part of an air compressor, or part of a Diesel engine.
If it decides the latter, and suffers a Diesel combustion event,
the cylinder will disintegrate, explosively.
You will likely not survive that event.
That is why hydraulic accumulators are charged with nitrogen, not air.
I think dieseling is a minor issue, but pneumatics are absolutely inappropriate for a log splitter. When the log starts to spltp there is no longer any control on the speed of the cylinder. It will move very fast in the sense of an explosion. Wood will fly, and there will be no opportunity to “get out of the way” of anything. Pneumatic cylinders can be speed controlled, but this does not work when they build-up to full load and then the resistance suddenly goes away. They behave just like a coil spring under such conditions. Very dangerous.
One work around is an “air-over oil system” where compressed air is used to apply pressure to oil in a tank, and then the oil moves the cylinder. The oil flow rate can then still be controlled. That is often used to lift and lower things. But for a splitter it is cheaper to just go straight hydraulic.
I’ve done a LOT of pneumatic work and it is always a last resort. Several reasons not explicitly listed above:
Any pneumatic operation will require 6-9 times more energy input than a similar hydraulic process would require to do the same work.
The amount of mass you have to add to the system to raise pressure will all participate in the explosion when (not if) some component fails.
When you use plastic pipe for a pneumatic power application you never know exactly when the outgassing of the plastic has lowered its ductility into the brittle-failure range. You only need to see a plastic pipe come apart with 100 psi on it once to never want to see it again
People who know me from eng-tips.com will attest that I am a huge proponent of pneumatic testing (or piping systems) over hydrostatic testing. In fact I’ve just completed a peer-reviewed paper titled “Comparative Risks of Hydrostatic and Pneumatic Pipeline Testing” for the ASME Journal of Pressure Vessel Technology (PVT-19-1222) that will be in the next issue. I have no problem dealing with very high pressure air and other gases, but having spent 50 years working around pneumatic processes tells me that there is a high likelihood that this project will end up with an entry on some newspaper’s obituary page.
I am not using plastic anymore I have upped it to 3/4" ID or sch 40 pipe. There are numerous other people doing this and I have not seen any obituaries. I promise to wear my motorcycle helmet on my first test run.