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 72 users online :: 3 registered, 0 hidden and 69 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Piston valve question

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

Piston valve question

Unread postAuthor: Labtecpower » Wed Sep 15, 2010 1:02 pm

I'm currently designing a piston valved BB-musket.
In my garage I had some stuff lying around, wich I think I can use.

I had my doubts about the Presta valve I wanted to use as a filling valve and the pilot valve.

I have 10.00 mm aluminium tube lying around, wich will make the piston.
It will slide in copper tube with an OD of 12 mm, and an ID of 10.04 mm.
According to my maths it will make a gap of 0.63 square mm.
Will it give me piloting problems with the presta valve?

Here are some pictures to give you an idea of the materials.


the aluminium tube

Image



Image

The copper tube. couldn't get the olive off :?

Image

my presta valve

Image

I'm looking forward to your replies!
  • 0

User avatar
Labtecpower
Major General
Major General
 
Posts: 1267
Joined: Sat Feb 20, 2010 6:38 am
Location: Herb Island
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 1:06 pm

Can you dismantle the presta to see what the effective flow area is? If it's bigger than the gap between piston and chamber you should be fine.

You could always wrap tape around the piston to reduce the gap further.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Labtecpower » Wed Sep 15, 2010 1:14 pm

I don't want to wreck too much presta valves, as they are pretty hard to get for me...
Wrapping my piston with tape won't work, as my thinnest tape is 0.03 mm,
for comparison, one of your hairs is about 0,04 mm.
if I have a spare presta I will do some medical examination :P
  • 0

User avatar
Labtecpower
Major General
Major General
 
Posts: 1267
Joined: Sat Feb 20, 2010 6:38 am
Location: Herb Island
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 1:17 pm

If a single layer of tape is too much, then you should be fine with a presta pilot. Just make sure you keep pilot volume to a minimum, piston travel doesn;t need to be more than 50% of your calibre.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Labtecpower » Wed Sep 15, 2010 1:23 pm

Thanks for the <1 minute replies :thumbleft:

I didnt know that such little travel was enough, but it will make things easier for me.
  • 0

User avatar
Labtecpower
Major General
Major General
 
Posts: 1267
Joined: Sat Feb 20, 2010 6:38 am
Location: Herb Island
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 1:40 pm

Labtecpower wrote: I didnt know that such little travel was enough


Read through this thread ;)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: saefroch » Wed Sep 15, 2010 4:57 pm

Prestas have about as much flow as a schrader, but they do require quite a lot of force to depress and open. I'd avoid using a presta as a pilot valve, and opt for a ball valve, blowgun, or pop-off instead.

It really depends on your pilot volume though... I say try it with the presta and if it proves to have oddly low performance, try a different pilot valve.
  • 0

User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 11:15 pm

saefroch wrote:Prestas have about as much flow as a schrader, but they do require quite a lot of force to depress and open. I'd avoid using a presta as a pilot valve, and opt for a ball valve, blowgun, or pop-off instead.


Nothing wrong with schraders as pilot valves, and if you use a lever/hammer to actuate the schrader, the force issue is negated.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: saefroch » Thu Sep 16, 2010 6:25 am

Oh, I'm fully aware you've used shchrader valves as a piltot/fill valves on multiple builds, just the flow demands very low pilot volume, which your builds have. Will this one though?

In actual answer to his question: I don't think you'll have problems with too much air leaking around the piston... just the piston might pilot slowly. In theory, a higher-flow pilot valve is better... in theory.
  • 0

User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Unread postAuthor: Technician1002 » Thu Sep 16, 2010 11:47 am

saefroch wrote:Oh, I'm fully aware you've used shchrader valves as a piltot/fill valves on multiple builds, just the flow demands very low pilot volume, which your builds have. Will this one though?

In actual answer to his question: I don't think you'll have problems with too much air leaking around the piston... just the piston might pilot slowly. In theory, a higher-flow pilot valve is better... in theory.


The low flow requires a tight fitting piston with a very small EQ port. Piston leakage becomes a very real obstacle in getting them to work.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Labtecpower » Thu Sep 16, 2010 11:54 am

I'm designing the pilot area now, and I think it will have less than 2 ccm of pilot volume.
would four hundreth of a millimeter space bug me?
the piston will have no equalisation hole, unless it proves to be absolutely neccassary.
I'm thinking of some sort of hammer to open my valve.
  • 0

User avatar
Labtecpower
Major General
Major General
 
Posts: 1267
Joined: Sat Feb 20, 2010 6:38 am
Location: Herb Island
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Thu Sep 16, 2010 3:52 pm

saefroch wrote:In actual answer to his question: I don't think you'll have problems with too much air leaking around the piston... just the piston might pilot slowly. In theory, a higher-flow pilot valve is better... in theory.


It is certainly better, but how much better in the case of a tight fitting piston and minimum pilot volume is debatable.

In this case, as there are no o-rings, there is absolutely no need for an equalisation port, indeed adding one could potentially increase leakage to the extent that it won't fire with a schrader/presta pilot.

I'm thinking of some sort of hammer to open my valve.


I would go with a lever, simpler to implement and on this scale you probably won't notice the difference in performance.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Labtecpower » Sat Sep 18, 2010 4:28 am

I have dismantled my presta valve in such way it can be used again, and I came to the conclusion that it in theory has a better flow rate than a schrader valve.
when you press the palve stem, the opened area is larger than the schrader's.
another advantage is that it doesn't leak air when detached from the pump, minimalising the risk of accidental firing.
should I post some close-ups of the guts?
  • 0

User avatar
Labtecpower
Major General
Major General
 
Posts: 1267
Joined: Sat Feb 20, 2010 6:38 am
Location: Herb Island
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Sat Sep 18, 2010 6:40 am

Labtecpower wrote:should I post some close-ups of the guts?


Yes please, maybe I'll regret ordering a lot of 50 schrader valves off ebay :roll:
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Return to Pneumatic Cannon Discussion

Who is online

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

cron
Reputation System ©'