Page 1 of 4

Sticky Piston

Posted: Fri May 16, 2008 4:11 pm
by daberno123
Today I took out my newly completed piston gun to test. I had tested the valve before, using a 1" modded sprinkler as a pilot, and thought it worked becasue of the loud noise it made when piloted.

However, after loading in a potato and squeezing the blowgun, no potato left the barrel.

It seems that my piston is sticking to the barrel, and all air in the chamber (40" of 2" PVC) is leaving via the sprinkler.

The specs on my piston valve are 1.5" porting housed in a 2" tee. The 1.5" pipe extends halfway into the tee.
I have two 1.25" caps as a piston with a sealing face bolted on using a .25" nipple and cap.
The sealing face is three layers of neoprene washers.
The piston is wrapped in a few layers of duct tape for a better fit and lubricated with white lithium grease so it slides easily.
It is piloted with a 1" sprinkler and pilot volume measures approximately 6 cu. inches.

Anyone have any ideas on why this is happening, and how I can fix it?
Any help is much appreciated.

Posted: Fri May 16, 2008 4:21 pm
by brogdenlaxmiddie
put some grease on it... thats what I would do... maybe some white lithium grease... put the grease on the sealing face ( if thats where u think its sticking)

Posted: Fri May 16, 2008 4:22 pm
by daberno123
I already did. Its in my above post.

Any other ideas?

Posted: Fri May 16, 2008 4:24 pm
by SpudFarm
hmm is your piston thin? mabe there is a gap from the chamber to the pilot side via behind the piston :D

Posted: Fri May 16, 2008 4:28 pm
by daberno123
If by thin you mean short in length, then I don't think so, but how short would be too short? The piston rests in a section of pipe and I don't think there are any gaps.

Posted: Fri May 16, 2008 4:28 pm
by jrrdw
Can you post some pics of it if you can. With the greese on it the duct tape shouldn't be causeing any problems. How loose does the piston fit? Any chance it is tipping and jamming? Is the barrel half way through the tee?

Posted: Fri May 16, 2008 4:33 pm
by SpudFarm
daberno123 wrote:If by thin you mean short in length, then I don't think so, but how short would be too short? The piston rests in a section of pipe and I don't think there are any gaps.
my valve it completely sealet behind the "gap" in the back of the tee. (equalizion holes (?) )

hard to explain so i make some crappy diagrams..

Edit: the diagram are in (ask)

Posted: Fri May 16, 2008 5:01 pm
by STHORNE
jrrdw wrote:brogdenlaxmiddie, I should delete your post but I'll leave it for the embarresment factor! Reread daberno123 post, then reread yours and read them very carefully. I think you will figure out what I'm talking about.
lol, now you're just being mean jrrdw... :? Ease up on him....he's only human lol.

Due to my slow typing brogdenlaxmiddle had edited and reposted the correction I did not see that not seeing the edit, lead me to post the above mentioned, that now makes no sense....... :oops: sorry.

Posted: Fri May 16, 2008 5:15 pm
by SpudFarm
HAHA STHORNE! the fish thing make me rofl :D

Posted: Fri May 16, 2008 5:21 pm
by jrrdw
Keep on topic guys, the next off topic post gets deleted with out notice!

Posted: Fri May 16, 2008 5:41 pm
by bigbob12345
:lol:
My post did get deleted
Well there, my point is proven if you got the opportunity to read it.

But back on topic(so this post doesnt get deleted too)
Check to see if there is any sticky part of the duct tape on the outside(I probably didnt word that very well)
I had the same problem with my first piston and it was solved by adding the duct tape cleanlyer(yes I know that isnt a word).
And how tight is your piston?

Posted: Fri May 16, 2008 5:52 pm
by jrrdw
bigbob12345 wrote::lol:
My post did get deleted
Well there, my point is proven if you got the opportunity to read it.
Hey Bob --
Moderator relations:
Moderators may deem a post inappropriate at any time, for any reason, and may delete such posts without warning.
A moderator may move an incorrectly placed post. If a post/thread appears to be gone, please check your recent topics (listed in your profile) to see if it was moved.
If you question a moderator's decision, please contact the moderator via e-mail. If you have a valid objection, the decision may be overturned. Public flaming of the moderators rarely has a positive effect.
Angering the moderators/admins is HAZARDOUS TO YOUR ACCOUNT'S HEALTH! Do so at your own risk.
These rules may not be complete. Intentional exploitation of loopholes may result in new rules.

Posted: Fri May 16, 2008 8:15 pm
by daberno123
Thanks for the diagram spudfarm. I took apart the valve and my piston is like the top left one, not the bottom left. It seems to have proper equilization holes. I tested it by blowing behind the piston. The air slowly leaked through, not in a rush like in the bottom left one.

Here are the pics jrrdw asked for
BTW, jrrdw, thanks for keeping this thread on topic for me.

This is the whole valve. I am fully aware of the massive pilot volume and there is no need to tell me about it.

Image

Piston in the housing

Image

The porting, halfway into the tee

Image

The piston itself

Image

Another picture of the piston, showing how tight a fit it is. I noticed the gash in it, but it doesn't seem to be affecting its travel at all. The piston moves easily with the push of my figure.

Image

Posted: Sat May 17, 2008 6:37 am
by jrrdw
BTW, jrrdw, thanks for keeping this thread on topic for me.


Your welcome.

I see a wrinkle/bulge in the duct tape. I would use a razor blade and slice it up the middle, lay it flat and trim off the essex tape. That will eliminate the possibility of that hanging it up. I see the gash half way/3rd of the way around the circumference of the piston, that is a sign of tilt type jamming. If the gash ran long ways then I wouldn't worry about it.

I also see the side clearance from piston to cylinder, a bit much in my opinion. Try another layer of tape and leave about 1/32nds of a inch gap in between the tape ends to act as a equalization hole. See what happens, keep us up to date please.

Posted: Sat May 17, 2008 8:17 am
by SpudFarm
good looking, i am agree with jrrdw here.. to much gap and some sort of jamming.

do you have the tools/time to make two simple o-ring grooves in it?
i wouls have taken the time to use the dremel tool to make two grooves. one at the front and one at the back.

mabe you can try to make a piston like the one on the diagram but add a neoprene washer longer back to?

first you have to try to make the piston fit so tight you feel a slight restistance (?) when you push it. more tape!