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Another incident with the QDV

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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Another incident with the QDV

Unread postAuthor: Ranger » Thu Jun 24, 2010 1:59 pm

I made another piston today with smaller O ring grooves so that it would seal better. It worked! It was filling up and it got to about 50 psi, then I heard a loud BANG ! And saw a piece of piston land next to me, I had no idea where the other pieces went. I looked in the barrel and found 2 out of 5 pieces in there so that makes 3 pieces. I kept looking and looking.... and looking! Finally I looked up :roll: There was a hole in the ceiling :lol:

These things are not toys, they are extremley powerful.
Here is where the gun was when I shot it
Image

Parts of the piston flew out of the barrel and hit this concrete ledge
Image

This is the ceiling tile...
Image

Thats where the ceiling tile was.
Image

All the parts of the piston, (minus 1 Oring)
Image

I make these pistons by cutting 2" circular holes with a holesaw in a cutting board and then heat them up and press them together. Then turn them down on a drill press. I guess when I heated and pressed them together, I didnt do it good enough. This happened on my first piston but I was able to break it with my hand, this piston took about 50 psi to seperate it.

Well, fourth times a charm... going to make another piston.
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Last edited by Ranger on Thu Jun 24, 2010 8:43 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Thu Jun 24, 2010 2:24 pm

Haha! Welcome to the ceiling piston club :D

Image

Seriously though, spudder's luck eventually runs out, some more care is needed in your experimentation...
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Unread postAuthor: SpudBlaster15 » Thu Jun 24, 2010 2:29 pm

jackssmirkingrevenge wrote:Image


This just made my day.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 24, 2010 2:42 pm

SpudBlaster15 wrote:This just made my day.


You can thank clide for the comedy gold :)
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Unread postAuthor: Technician1002 » Thu Jun 24, 2010 3:21 pm

I worried about that exact failure mode when I made my first laminated piston. To prevent that failure, I decided to laminate it the long way. It held up nicely. I really liquefied the faces of the plastic as my early attempts to make the laminations thin failed. A deep melt so it behaves like a grilled cheese sandwich did the trick.
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Attachments
Squished valve core.JPG
Looking at the side of the core after most of the laminations are added.
Squish together.JPG
A good lamination squished out lots of liquid plastic in the process. HDPE turns clear when melted.
Polyethelene laminited - other plastic failed.jpg
WMHWPE and many other plastics do not heat laminate. I tried some. It simply doesn't melt to a squishable liquid and comes apart. If it doesn't turn clear and become like melted cheese, you have the wrong stuff.
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Unread postAuthor: Ranger » Thu Jun 24, 2010 4:35 pm

I knew you must have had similar problems Technician...

I do have HDPE, it turns clear when heated. On this next piston (which I'm making ATM) I am really heating up the plastic, I'm taking no chances this time.
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Unread postAuthor: kydavies » Thu Jun 24, 2010 4:37 pm

jackssmirkingrevenge, is that your piston in the ceiling?
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Unread postAuthor: POLAND_SPUD » Thu Jun 24, 2010 4:49 pm

This just made my day
lol same here :D
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Unread postAuthor: deathbyDWV » Thu Jun 24, 2010 7:55 pm

POLAND_SPUD wrote:
This just made my day
lol same here :D

Same here too... I'm fairly sure that made everyone's day that looked at it... :lol:
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Unread postAuthor: Technician1002 » Thu Jun 24, 2010 8:14 pm

50 PSI indoors with a projectile on the loose and the roof falling in, I gotta ask, did you soil your shorts? :D

Indoors I bet it was loud. I have dumped mine at 50 PSI (no projectile) indoors and the noise is very impressive.

I try to think what could possibly go wrong and try to plan so it can't happen. Just in case it does anyway, I make sure down range is clear.
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Unread postAuthor: Ranger » Thu Jun 24, 2010 8:47 pm

Technician1002 wrote:50 PSI indoors with a projectile on the loose and the roof falling in, I gotta ask, did you soil your shorts? :D


No, I just sat there for a minute wondering what the f*** happened and then started laughing.

From now on, I'm going to do all of my tests outdoors and be prepared for anything to go wrong.
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Photo of my lamination job

Unread postAuthor: Technician1002 » Thu Jun 24, 2010 9:23 pm

I looked for a good photo of my finished piston to show the laminations, but couldn't find one. I pulled the piston to get this close up shot.

Note, the o ring groove is narrow. The ring has little side play, but still loose in the groove, Note the top floating ring is hanging out on the left side. It is free to move in the groove.
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Attachments
PistonLaminations.JPG
QDV Piston. Various amounts of squish makes a weird pattern. I don't worry about a bad lamination causing a part of the piston to launch. Chamber pressure squeezes it together, not pull it apart.
Last edited by Technician1002 on Thu Jun 24, 2010 10:56 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 24, 2010 10:48 pm

kydavies wrote:jackssmirkingrevenge, is that your piston in the ceiling?


Can't be, no epoxy on it ;P

It's from clide's golf ball launcher, letting you know the importance of a good bumper ;)

If I did have a false ceiliing in my room though it would have at least 3 major perforations, so I won't judge :roll:
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Unread postAuthor: Technician1002 » Thu Jun 24, 2010 10:51 pm

I mix epoxy on HDPE. It doesn't stick. I wait for it to harden and peel it off. I doubt epoxy would have prevented the failure of the HDPE piston. :shock:
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 24, 2010 11:04 pm

Technician1002 wrote:I mix epoxy on HDPE. It doesn't stick. I wait for it to harden and peel it off. I doubt epoxy would have prevented the failure of the HDPE piston. :shock:


Have you tried roughening the surface properly?
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