Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 54 users online :: 4 registered, 0 hidden and 50 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Balanced UnBalanced 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.
Sponsored 
  • Author
    Message

Balanced UnBalanced Piston

Unread postAuthor: airatomic » Fri Jul 14, 2017 3:42 am

Hello,

Does anyone know, in this scenario, will the piston move to the right, or remain stationary (as in QDV)?

balanced_unbalanced_piston.jpg
balanced_unbalanced_piston.jpg (17.43 KiB) Viewed 608 times
  • 0


airatomic
Private
Private
 
Posts: 8
Joined: Sun Sep 04, 2011 9:33 pm
Location: Hawaii
Reputation: 0

Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Fri Jul 14, 2017 6:54 am

It will move towards the right so quickly that limp wristed Antifa "activisits" will show up to riot in protest :D
  • 2

Last edited by jackssmirkingrevenge on Sun Jul 16, 2017 7:56 am, edited 1 time in total.
User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24532
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 84

Re: Balanced UnBalanced Piston

Unread postAuthor: farcticox1 » Fri Jul 14, 2017 5:55 pm

I think right is the right answer :shock:
  • 0

User avatar
farcticox1
Captain
Captain
 
Posts: 304
Joined: Sun Mar 31, 2013 12:37 pm
Country: Canada (ca)
Reputation: 31

Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Sat Jul 22, 2017 10:37 pm

I had my suspicion about it before posting, but just wanted confirmation from the experts here. ;)

How about this one? The o-rings are not on the piston but on the piston valve body (what you call this type of piston + grooves)? Will the piston move to the right?

balanced_unbalanced_piston2.jpg
balanced_unbalanced_piston2.jpg (18.02 KiB) Viewed 480 times
  • 0


airatomic
Private
Private
 
Posts: 8
Joined: Sun Sep 04, 2011 9:33 pm
Location: Hawaii
Reputation: 0

Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Tue Jul 25, 2017 6:07 am

This will also move to the right for the same reasons - the force around the o-rings is balanced, but there is nothing to oppose the force on the base of the piston:

unbalancedvalve.png
unbalancedvalve.png (15.39 KiB) Viewed 473 times
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24532
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 84

Re: Balanced UnBalanced Piston

Unread postAuthor: farcticox1 » Thu Jul 27, 2017 6:37 pm

Use the force
  • 0

User avatar
farcticox1
Captain
Captain
 
Posts: 304
Joined: Sun Mar 31, 2013 12:37 pm
Country: Canada (ca)
Reputation: 31

Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Thu Aug 10, 2017 1:42 pm

And so, its Plan B then, since the previous diagrams logic ain't working.

Plan B:

3way_slide.jpg
3way_slide.jpg (37.6 KiB) Viewed 265 times


To make it, obviously you need to make "rod seal" type, which is head-scratching, since "piston seal" is easier and more common. Materials: solid rod (got to make 2 inline holes with exits at appropriate distances), matching o-rings, and the body (I used ABS tube and knowing for sure, it wouldn't crack - as the fiberglass body would have to crack first) with fiberglass casting.


1) Rod with o-rings, ready for fiberglass casting deployment. Be sure to oil the rod's body first.

DSC_2343.JPG



2) 24 hours later, and poking the rod out, revealing the fiberglass body, with o-rings exactly where they supposed to be:

DSC_2353.JPG


3) Epoxied (JSR gonna like this) the threads to the rod's body. Since all the parts of my launcher are "serviceable", had to create ways to make this slide valve serviceable too, esp the o-rings, if need replacements.

DSC_2402.JPG


4) Ready to test:

DSC_2416.JPG


Comments: Sadly, there are leaks. I wondered if the o-rings were misplaced, or the cast body got leaks, but no, the problems was the o-rings area, where the edge/sides covering the o-rings have some "casting imperfections of fiberglass". I was genuinely !@#$%^&*

5) A day later, decided to make another one, with better precisions in the casting. Ex: wiping off any greese from the o-rings before casting:

DSC_2419.JPG


Conclusion: Same leaking issues as the first one. No matter how careful, the casted edges of the o-rings always have some sort of imperfections, creating paths for leaks. I am beat.

Anyone with better ideas of casting, so that the edges surrounding the o-rings are "perfect"?
  • 0


airatomic
Private
Private
 
Posts: 8
Joined: Sun Sep 04, 2011 9:33 pm
Location: Hawaii
Reputation: 0

Re: Balanced UnBalanced Piston

Sponsored

Sponsor
 


Re: Balanced UnBalanced Piston

Unread postAuthor: Anatine Duo » Sat Aug 12, 2017 5:27 am

interesting problem! I would try lower viscosity epoxy, maybe no fiberglass (is it the glass flocking you are using or longer strands?)

Also if you can improvise a vacuum chamber maybe you can pull some bubbles out before the epoxy cures.
  • 0

User avatar
Anatine Duo
Sergeant
Sergeant
 
Posts: 84
Joined: Sat Feb 01, 2014 11:16 am
Country: Canada (ca)
Reputation: 5

Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Sat Aug 12, 2017 5:41 am

I recognize that construction method :) are the o-rings tight around the rod though? If you don't have to stretch them to fit them, you will never have a good seal under pressure. They look pretty loose and I think that is your main issue.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24532
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 84

Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Sat Aug 12, 2017 11:47 am

JSR. a day after the second attempt, i had that thought exactly. The orings only had "nice fit" on the rod. Not loose, nor too tight, but just nice. Even the rod slides in and out rather easy. Interestingly, if i rotate the body around, at some point, the leaking just stops.

And so, this gives another incentive to try the third attempt, this time with tighter orings around the rod. I have this question though: if i use tighter orings around the rod (having to stretch them on the rod), what will happen to the orings and their sockets after casting is done, and the rod poked out? Will the orings return to their smaller dia (pre-stretch) and come off from their sockets? Or the sockets would be tight and hold on to the orings' exaggerated stretched dia?

A.Duo, the fiberglass resin + MEKP mixtures have very low viscosity. I used these mixtures before to replicate gun's body shape from hollow toy guns, and details were amazing. I am sure JSR can testify to its viscosity. ;)
  • 0


airatomic
Private
Private
 
Posts: 8
Joined: Sun Sep 04, 2011 9:33 pm
Location: Hawaii
Reputation: 0

Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Sun Aug 13, 2017 3:24 am

airatomic wrote:I have this question though: if i use tighter orings around the rod (having to stretch them on the rod), what will happen to the orings and their sockets after casting is done, and the rod poked out? Will the orings return to their smaller dia (pre-stretch) and come off from their sockets? Or the sockets would be tight and hold on to the orings' exaggerated stretched dia?


As long as there isn't too much of a difference in diameter between rod and unstretched o-ring - I would say less than 1mm - they should remain in their groove.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24532
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 84

Re: Balanced UnBalanced Piston

Unread postAuthor: mrfoo » Sun Aug 13, 2017 11:06 am

Pulling a vacuum on your epoxy will almost certainly improve matters. For your construction method, I would look at casting the inner portion, with the o-rings, as pure epoxy with no reinforcement, and then casting the reinforced bit over the top.

Or, if you have access to a lathe, turn it from metal.
  • 0

User avatar
mrfoo
Corporal
Corporal
 
Posts: 62
Joined: Wed Apr 29, 2015 11:05 am
Country: Afghanistan (af)
Reputation: 5

Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Mon Aug 14, 2017 7:00 pm

MrFoo, can you pull out some diagrams to explain your methods?

All these years on spudding, i only used a drill press, grinder and lots of epoxy (yah!). Coz that's all i have.
  • 0


airatomic
Private
Private
 
Posts: 8
Joined: Sun Sep 04, 2011 9:33 pm
Location: Hawaii
Reputation: 0

Re: Balanced UnBalanced Piston

Unread postAuthor: mrfoo » Tue Aug 15, 2017 2:09 am

I'm crap at drawing :)

Shaft seals are hard to do without the proper tools, "the proper tools" being a (preferably collet) lathe and an internal groove cutting tool. Still, I think you should be able to get an acceptable seal as long as you're willing to live with a certain amount of "stiction" (I can't see an easy way of casting a groove for a floating O-ring) as long as you're careful.

The only bits that really need to be "clean" are the groove edges, that's where air pressure is going to leak around your o-rings. For that, you need epoxy with no bubbles or other surface imperfections. Glass fibre will give you surface imperfections (and bubbles). Even the mechanical process of mixing resin will put bubbles in, and you need to get them out before using the resin. Mix resin in a container / cup, put it in a vacuum vessel, pull a vacuum on it, wait a few minutes for the bubbles to pop out, use resin. Easy as. My vacuum vessel is an old pressure cooker, but you should be able to get away with anything relatively strong that you can get a hose onto and seal the rest. For pulling the vacuum, I use the "wrong" end of a fridge compressor. Google "fridge compressor vacuum pump", you'll get loads of hits, although for outgassing resin you don't need any valves or vacuum accumulators, just a hose from the pump to the container.

As you only need the bits around your o-rings to be "clean" cast, mix up just enough resin to cover your o-rings, pull the bubbles, put it over your o-rings and leave it to set for a while. Once it's gelled, cast the rest with the fibre reinforcement.

Personally, I'd try and work out a way of casting grooves for floating o-rings, but that's not going to be easy.

Alternatively, with a couple more o-rings and you can put the seals on the rod and port the barrel, which might be easier to deal with overall, it'll certainly be easier to change the seals if you need to.
  • 0

User avatar
mrfoo
Corporal
Corporal
 
Posts: 62
Joined: Wed Apr 29, 2015 11:05 am
Country: Afghanistan (af)
Reputation: 5

Re: Balanced UnBalanced Piston

Unread postAuthor: Gippeto » Tue Aug 15, 2017 9:28 am

Any chance of finding the right size tube to use between the o-rings? Short sections of tube sanded square using the drill press....

Have yet to buy a vacuum pump for the garage, but I did have an old piston type compressor kicking around....couple fittings and a 1/2" needle valve from the junk bin threaded into the inlet and.....
  • 1

Attachments
20170718_114246.jpg
"It could be that the purpose of your life is to serve as a warning to others" – unknown

Liberalism is a mental disorder, reality is it's cure.
User avatar
Gippeto
Donating Member
Donating Member
 
Posts: 2424
Joined: Sat Jan 19, 2008 10:14 am
Location: The Great White North...Canada eh!
Reputation: 17

Next

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], Yahoo [Bot]

Reputation System ©'