Make air cylinder pneumatic can crusher

by Doug McCrary
(San Diego, CA USA)

Overall view pneumatic can crusher

Overall view pneumatic can crusher

Overall view pneumatic can crusher
Close-up pneumatic can crusher

Two or three, actually:

This is used mostly for 12oz cans, but can handle 24oz cans.

Small cans crush nicely at about 85 psi, while large cans need closer to 110 to fully crush.


I made up the thing shown in the first pic so I can turn on either regulated 85 or unregulated 100-125 air. (there are two filters in the line to the blue hose, and I plan to add another one right before the FR in the picture).
The second picture shows a 120z can just prior to crushing.

1. does it matter to the cylinder whether it is pressurised when not in use?

2. would putting between the cylinder and the ram to keep it from fully retracting while crushing small cans hurt anything?

3. other comments? The blue hose will eventually drop straight down, but I have not seen any moisture issues.
Doug, good on you. One of these has been on my to-do list for a long time, and I have never got around to it.

Question 1) No, the air cylinder will suffer no ill effects if left pressurized. If, however, you have a cylinder piston seal leak, then air will blow by, and your air compressor will cycle for nothing if the leak is not repaired.

2) If this ... "would putting between the cylinder and the ram " means you want to put a stop of some sort, no, the cylinder doesn't care where the rod stops. If the stop is stronger than the force generated by the cylinder, the piston inside the cylinder just halts travel.

Suggestion... though the can cover is closed when the action cycles, what if it isn't? You have created a potential pinch point. Get around that by adding an anti-tie down circuit that requires two buttons, arms-length separated, to be pushed and held to cycle the air cylinder. That way both hands have to be away from the crusher when it is moving.

Also, why not run it at the higher pressure all the time? A single cycle of the crusher will use very little extra air, and it will always be at the pressure needed to handle the big cans. If the crusher air cylinder moves too fast, simply add a flow control that slows the cylinder, but does not take away any of the force.

Thanks for this. Good one!


Comments for Make air cylinder pneumatic can crusher

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Aug 18, 2013
by: Doug in

1. OK, that's what I thought.

2. Yes. Sorry I left out the noun. I'm thinking a piece of angle iron with a finger hook or something to make it easy to add/remove.

3.Regarding the cover, perhaps you were lead astray by the second picture? The air was off for that, just to show scale. The cover normally activates the 5/2 switch when closed and pushed down, so unless I use the little "pusher" hanging off the wire wrap, it's not going anywhere...

Regarding air consumption, you might be surprised!
Given a fully charged tank, with the full stroke:
at 85 psi, I get fully 11 cycles before cut-in.
at 100-125 psi unregulated, only 8 cycles.

That's a 2in bore, 8in stroke, so I expect to from 11 to probably 14 small cans with the lower pressure and about a 5-1/2in stroke with the stop in place. I'll be putting that in with the air supply off.

All that 'cause you pointed out that air is expensive!

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Can crusher leaking problem

by Doug McCrary
(San Diego, CA USA)

40 minutes after valve closed

40 minutes after valve closed

So, you can see from the pic I got the primary air filter added to the main air.

Also see that the valves are both "off", and there is very little air reserve between the (red handle) valves and the crusher switch/cylinder.

If I were doing an air brake check on a vehicle, 3psi loss in one minute would be acceptable. This system bleeds about 1psi per minute.

I don't yet know if it's the cylinder or the switch or both doing the leaking. Gotta get some caps/plugs to do that.

The question: is there a rule of thumb or whatever for acceptable leakage?
As far as I know it's user determined, Doug. A major plant might blow off 10% of their air production to dozens of leaks and find that acceptable and a single fixture that leaks at all may throw off a clamp mechanism leading to product failures, and in that case, no leak at all is their norm.

If you don't want to waste air through a small leak, and couldn't be bothered finding it, install a ball valve before the system to shut off the air there.

You don't need caps to check your cylinder. Pressurize the system, then fold the line that is pressurized to the cylinder. Feel at the exhaust port of the valve. If air is leaking out of the exhaust port of the valve and it stops when you clamp the pressurized air line going to the cylinder, then the leak is in the cylinder. If the air continues to leak out of the exhaust of the valve with the pressure line to the cylinder clamp, then you have a seal leak in the valve.

Soap and water will find any fitting leaks.



Comments for Can crusher leaking problem

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Aug 25, 2013
by: Doug in


The two red handle valves close off the leak, so it's not leaking when not in use.

If I don't use caps or plugs, I'll have to replace the brass compression fittings at about $3.50 per pair: the tubing weakens or cracks when bent.

I guess I should look into different tube. This is stuff I had on hand at the time.

Other leak (the worst one) is found and fixed.

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Can crusher air gauge leak!

by Doug McCrary
(San Diego, CA USA)

A remark, actually...

In addition to what you already have on the gauge page, there is at least one more failure mode: leak(s).

I had an air tank that had been working ok for some time...

Then, overnight, it went from 120psi to 60psi.

Went looking for leaks, couldn't find any.

Finally realised that while it went from 120 to 60 overnight, it then didn't leak down further.

Knowing how most gauges work, I concluded the gauge must be cracked internally.

It was: new gauge, leak gone.


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