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Pneumatic Golf Ball Launcher - Piston Problems

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: al-xg » Fri Oct 02, 2009 3:06 pm

:shock: Whatch out or the epoxy man will get you for the cheek of displaying such a picture ;)
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Unread postAuthor: MrCrowley » Fri Oct 02, 2009 4:48 pm

Mabe australian fittings are different in AUS or just that the standard pn 18 ones found in Bunnings are chunkier, but i tried this method once and found that the threads intruded ~ 1mm into the pipe not allowing my piston through. Was the piston o-ringed so it was able to squeeze through?

I assume you're talking about the 2" female threaded adapter...

I found two types, one that lets the piston through and one that doesn't. Bunnings in NZ had the type that let the piston through. I'm not sure if that's because it had a different pressure rating or because it was a different brand. Either way, they do exist.

Go to Reece's or some other plumbing merchant and look there.
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Unread postAuthor: rikukiakuchiki777 » Fri Oct 02, 2009 11:35 pm

tghhs wrote:So did you manage to make the piston servicable? Also i did you manage to get a good bumper for that piston?


Nope, unfortunately the piston is not serviceable however it works which is the main thing (thanks again to everyone for helping :D:D ). The bumper is about 1cm of sponge with a hole cut in the middle. It restricts the pistons movement a little however it works really well. The piston still opens about ~1.8cm though so airflow is not restricted substantially.

I've still got a few things to work on; I've got a leak to fix thats quite difficult to get access to but after that I'm focusing on aesthetics and damage vids :D :roll:
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Unread postAuthor: MrCrowley » Fri Oct 02, 2009 11:57 pm

1cm of sponge

If you are talking about a normal sponge used to clean things, that will definitely not be enough. Last I recall, they're pretty damn easy to crush.
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Unread postAuthor: tghhs » Sat Oct 03, 2009 12:13 am

MrCrowley wrote:
Mabe australian fittings are different in AUS or just that the standard pn 18 ones found in Bunnings are chunkier, but i tried this method once and found that the threads intruded ~ 1mm into the pipe not allowing my piston through. Was the piston o-ringed so it was able to squeeze through?

I assume you're talking about the 2" female threaded adapter...

I found two types, one that lets the piston through and one that doesn't. Bunnings in NZ had the type that let the piston through. I'm not sure if that's because it had a different pressure rating or because it was a different brand. Either way, they do exist.

Go to Reece's or some other plumbing merchant and look there.


Yeh i was, should have said. Good suggestion as i have a Reece close to me i'll check out
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Unread postAuthor: rikukiakuchiki777 » Sat Oct 03, 2009 7:27 am

MrCrowley wrote:If you are talking about a normal sponge used to clean things, that will definitely not be enough. Last I recall, they're pretty damn easy to crush.


Well it is only my first pneumatic launcher, I don't really don't mind if it fails dramatically. I KNOW it works at 40psi so if thats all i can take it too, so be it :roll:. Everyone has to start somewhere :D
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Unread postAuthor: rikukiakuchiki777 » Sat Oct 10, 2009 3:16 am

Well I fixed the leaks, there is only a minor, extremely small leak remaining. However the cannon doesn't work anymore - I connect the air compressor, the pistons seals against the barrel, it fills the chamber for couple of seconds and then the air just starts leaking down the barrel. The cannon doesn't fire, it just vents a lot of air. I suspect the rubber seal on the piston is inadequate and when the pressure equalizes it pushes the seal back a bit and vents. Anyone got any other ideas?
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Unread postAuthor: tghhs » Sat Oct 10, 2009 3:56 am

if possible cover barrel when filling and when it starts to get to much open it. This will push your piston up against the barrel harder than it would when normally filling which may give you the better seal that you require.

This worked for me with one of my first cannons when it wouldn't seal properly. If this doesn't work there's not much we can do and we wont know what the problem was until it's taken apart, which will destroy it :(

Just something to learn from with your next one.
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 10, 2009 3:58 am

al-xg wrote::shock: Watch out or the epoxy man will get you for the cheek of displaying such a picture ;)


It does look like the foot was put there on purpose :roll: :D
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Unread postAuthor: rikukiakuchiki777 » Sat Oct 10, 2009 7:47 am

tghhs wrote:if possible cover barrel when filling and when it starts to get to much open it.


Alright will-do. I've already got plans to start a new one, with a better piston etc. This was just an expensive ($150 AU :shock: :roll: ) learning curve.

jackssmirkingrevenge wrote:It does look like the foot was put there on purpose


:D Well see; I had two photos of the cannon - one with and one without my hobbit foot. I had heard rumors of this 'epoxy man' and his foot fetish and seeing as this was my first cannon post I thought I would post it and see what happened lol.
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Unread postAuthor: rikukiakuchiki777 » Wed Oct 14, 2009 2:04 am

Well I've gone out and bought some new things for another gun. This one will be serviceable, but they didn't have 2.5" fittings so I had to cram it in a 2" tee. I did however find some pressure rated pipe with an inside diameter that perfectly fits golf balls - I think it may be SDR21 1.5" pipe, but the guy didn't know. The only dilemma I have is this:

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The barrel (the central pipe) inside a piece of 2" pipe. As can be seen, there is little space between them (about 1mm from the outside, when the pipe is in the direct center). Will this be an inadequate amount of space? or does there need to be more surface area for the piston to fire (oh I've yet to build it, but it will most likely be plywood).

The only other option I have is using a slightly less pressure rated 2" pipe with a larger inside diameter (53mm). This leaves plenty of surface area, however I will need to sand out a fitting in order to make the slightly larger piston slide through it. Advice? :D
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Unread postAuthor: psycix » Wed Oct 14, 2009 5:04 am

You should cover the pipe in epoxy or fiberglass (or some other kind of filling material) before sleeving to fill up the gap. The 1mm space may be too large.
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Unread postAuthor: rikukiakuchiki777 » Thu Oct 15, 2009 1:13 am

psycix wrote:You should cover the pipe in epoxy or fiberglass (or some other kind of filling material) before sleeving to fill up the gap. The 1mm space may be too large.


I think you may have misunderstood me sorry. The larger, outer pipe is 2" sch 40 that will be inside the 2" tee. The piston will slide inside this 2" pipe. The barrel is the smaller pipe, and the piston seals against this. As you can see, there is only ~1mm difference in diameter so my question was this: will there be adequate surface area to open the piston when the pilot area is vented?

Sorry for the misunderstanding.
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Unread postAuthor: MrCrowley » Thu Oct 15, 2009 1:23 am

Well as the 2" pipe wont be able to sleeve the entire tee, as the tee has a 'lip' which stops fittings being glued too deep inside the tee, the barrel would extend out about 1/2 way in to the tee...which is past the lip.

Although 2" pipe and the lip inside the tee have roughly the same diameter, the lip stops short at the half way mark in the tee on the bottom half as there is the downward port. So if your barrel is halfway in to the tee, and the piston seals against that, there's plenty of surface area to push your piston back because of the opened space where there is the third port.
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Unread postAuthor: rikukiakuchiki777 » Thu Oct 15, 2009 1:53 am

@MrCrowley - In regards to your last post on my topic (thanks again for all your help), I understood what you meant but I'm still unsure so I've taken this picture:

Image

The deodorant can piston sitting on top of the barrel. The sealing face will be flat of course and the barrel cut straight, but as you can see there is little surface area. Will this matter, as you say the piston is exposed to the chamber port.

Sorry for the frequent and most likely stupid questions, but I am a newb and I just want to get this cannon perfect after the last failure :(
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