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The best type of material to use as a piston?

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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The best type of material to use as a piston?

Unread postAuthor: mattyzip77 » Sat Aug 27, 2011 10:43 am

Just what the title says! What is the best thing you have used for a piston? Pictures help. I have made this topic to help myself and other new people to the forum to give ideas about what to use, and or what has been used in the past for a piston. Currently I am just using a 1 1/4 inch coupler plugged at both ends with a neoprene washer for a sealing face with a steel washer behind it held together with a carraige bolt inside of a 2 inch pvc schedule 40 nsf pw rated Tee.
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Unread postAuthor: wyz2285 » Sat Aug 27, 2011 11:01 am

what ever that works strong and light :roll:
personally I like pistons made of bolts and washers with o-ring seal :wink:
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Gun Freak » Sat Aug 27, 2011 11:03 am

I agree with wyz, I like bolt/washer pistons.
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Unread postAuthor: Labtecpower » Sat Aug 27, 2011 11:10 am

I disagree, I like pistons machined out of light material :D It could also be because i never got a bolt/washer piston to work...
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Unread postAuthor: velocity3x » Sat Aug 27, 2011 11:16 am

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Unread postAuthor: wyz2285 » Sat Aug 27, 2011 11:31 am

@labtecpower not everybody can have a machined piston, and washer pistons works as well as a machined piston and they are light :roll:
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Technician1002 » Sat Aug 27, 2011 11:48 am

HDPE. It works well and is not difficult to "Machine" on a drill press.

HDPE
Image

http://www.spudfiles.com/forums/tutorial-making-a-small-o-ringed-piston-on-a-drill-press-t21740.html

Second best is UHMWPE

HDPE can be heat laminated. My 2 inch pisotn is laminated from an old HDPE cutting board.
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Unread postAuthor: Brian the brain » Sat Aug 27, 2011 12:14 pm

I'd like to share my experience with HDPE:
Fellow Dutch spudder Psycix made one for me, as well as a new aluminium top for a metal solenoid valve wich would turn it into a piston valve.

It worked great at first, the piston ran super smooth, was featherlight and very responsive.. The piston design provided much better flow than the original top and diaphram.

A couple of months later I wanted to use it again and the piston was stuck in its housing as it had soaked up lubricants and expanded.

Not just stuck...fused almost!

So...it's not suited for use with fridge compressor ( lubricants in the air) or...you'll have to either pre-soak the material before machining it or use less tight tolerances.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Technician1002 » Sat Aug 27, 2011 12:19 pm

Hmm, It would be nice to know which lubricants cause swelling and which are safe. I wonder if UHMWHDPE is resistant to the oils. I have not had any problems with swelling with the piston in the Marshmallow Cannon. I have noticed some minor swelling with the 2 inch piston, but not enough to cause serious binding yet.
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Unread postAuthor: Labtecpower » Sat Aug 27, 2011 1:16 pm

I have experienced the same effect with my nylon piston. Currently it is stuck in my copper gun, so I can't shoot it anymore.

The PVC piston in my QDV is still working great. It had a 0,025 mm space on each side of the piston, so I would have noticed any swelling.
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Unread postAuthor: Technician1002 » Sat Aug 27, 2011 1:30 pm

As noted, my PVC pistons did not swell. They tended to crack instead. They did not always crack at an impact point. Pipe cap pistons most often broke a hole in the centre of the piston face or on the side as shown. This piston is a 1 inch PVC pipe cap sanded down to fit a 1.5 inch PVC pipe.
Image

Pipe cap piston in place inside 1.5 inch pipe inside a female coupler.
Image
This was my favourite material until I upgraded to HDPE.
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Last edited by Technician1002 on Sat Aug 27, 2011 1:33 pm, edited 1 time in total.
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Unread postAuthor: Brian the brain » Sat Aug 27, 2011 1:33 pm

I imagine that the swelling is fairly limited. If you'd keep some clearance and use O-rings to center and seal it, it would probably not jam so badly.

The piston Psycix made for me moved freely but sealed without having O-rings...I cut a tiny channel into the side to allow it to pass air..but only opened up when the piston was fully closed...
A dream fit at first, but no tolerance to swelling... :wink:
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: velocity3x » Sat Aug 27, 2011 1:55 pm

Brian the brain wrote:A dream fit at first, but no tolerance to swelling.

Are you sure the dimensional instability of the piston wasn't due to temperature?
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Unread postAuthor: Brian the brain » Sun Aug 28, 2011 7:57 am

No, I'm not sure.

I saw a big red truck with blue lights and a ladder on it's roof with 4 helmet wearing guys with hoses putting out a fire,and jumped to the conclusion it was the firebrigade.

:D

The temperature inside my house is always kept " comfortable," within a couple of degrees celcius..
I doubt that say 10 degrees max difference could have caused it but...no I'm not sure
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: velocity3x » Sun Aug 28, 2011 9:58 am

Brian the brain wrote:The temperature inside my house is always kept " comfortable," within a couple of degrees celcius..
I doubt that say 10 degrees max difference could have caused it but...no I'm not sure


It was just a thought. I make my Acetal pistons with only a .001" wall clearance in an aluminum housing. They work perfectly in the machine room (72F). One day, I moved my first creations to the un-airconditioned part of my shop (105F). I had to drive out the piston with a pipe and sledge hammer. It was due to thermal expansion. I slightly reduced the piston diameter and it never happened again regardless of the temperature.
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