SpudFiles

G'day all,
I have a few questions which I hope you guys might be able to answer.
I have a scuba tank and the first stage brings down the pressure to about 140/150 bar.Edit: its 140/150psi....sorry about that. Is there a way you have heard of to increase that pressure?


Also I have bodgied together a polyurethane rod piston with electrical tape around it for my copper nightmare. Using a blowgun as an exhaust didn't work for me so I ended up using the blowgun to exhaust a QEV to dump the air behind the piston.
I realise this is excessive but it was the only way to get the piston to work.
Why is it that just using the blowgun it doesn't dump fast enough to release the piston. Is it the dodgie piston or does it really have to be a great fit?
Due to the small chamber I have to be able to open the piston fast.
I really wanted to put 300+psi through it but looks like 150/200 is as far as I can get with what I have.
I am rebuilding a piston this arvo (hopefully) on a lathe to cut some grooves in it for o rings.

Anyway a few things about my copper nightmare
Barrel length 1085 mm with a 10.8mm bore.
chamber 400mm 23mm inside bore.
With the barrel being inside the chamber I don't know the volume and I can't work it out

Don't know the pilot volume but it aint much

piston it 300mm long and has a travel of 10mm.

Edit: piston is 30mm long and travels 10mm

the piston should be able to slide around without too much friction.
your pistion is 300mm long ??!! haha think you may have made a mistake there mate. when you turn the new piston, dont worry about o-rings. just make sure there is room for it to move in the chamber and add a bit of electrical tape.

Cosmic Muffin wrote:the piston should be able to slide around without too much friction.
your pistion is 300mm long ??!! haha think you may have made a mistake there mate. when you turn the new piston, dont worry about o-rings. just make sure there is room for it to move in the chamber and add a bit of electrical tape.

Yeh, sorry, I was thinking of something else 300mm long

You wouldn't believe it but my neighbour turned me a piston out of aluminium and it works too well.
I have removed the QEV and I am piloting it from the blow gun but as soon as I try to remove the connection from the schrader valve it pilots and loses pressure.
I can't win.
I knew this was gonna be a learning experience but bugger me it is starting to get my goat

Now you know why I called it copper nightmare

forget about shrader valves... buy a male quick connect fitting and put it instead of the nozzle on the blowgun (it has threads right ??)... in this way you could also get rid of that T (and greatly reduce pilot volume)

ohh.... you'll need a female qc one your air source as well, but that goes without saying

140/150 bar

that's a typo right ?? 50 bar would be more than you need

I believe you mean 140 psi, 150 bar is a lot. 150 bar is around 2250 psi and there's no way the blowgun is taking that, you'd have to apply masses of force to activate it anyway..

Looks very good, the finish on the piston seems slightly rough but I bet it works very well with the rings!

If you don't want removing the air source to pilot your gun you could add a check valve or ball valve behind it, or use an attachment that leaks no air, such as a shock pump.

Poland, I believe blowguns are only intended to handle flow in one direction, you could try it thoguh.

Good job

Blowguns will handle flow in either direction. I've used them either way many times.

As for your piston-piloting-dilemma, I would install a check valve before the schrader valve. A schrader closes at a speed that is a function of how quickly you can disconnect it. A check valve is already closed when it comes time to unhook your air source (both the sides have equal pressure), so there's no air loss.

One can be made in a pinch, but you should be able to find a small one somewhere.

Also, that piston is looking good, but how does air equalize through or around it?

Poland, I believe blowguns are only intended to handle flow in one direction, you could try it thoguh.

they can handle flow in both dircetions but one side will leak if pressurised...
my suggestion is to add a male qc to the other side of the blowgun (if the other port is threaded - I've never used this type of blowguns so I don't know if it's threaded)...

it would only need to hold air in one direction

mark.f wrote:Also, that piston is looking good, but how does air equalize through or around it?

Good point, I would have the piston be an exact fit and remove the o-rings alltogether - no equalistation problems and much less friction.

jackssmirkingrevenge wrote:

mark.f wrote:Also, that piston is looking good, but how does air equalize through or around it?

Good point, I would have the piston be an exact fit and remove the o-rings alltogether - no equalistation problems and much less friction.

Floating rings work well. A calibrated bleed port in the piston is easier to adjust than piston fit.

Not only that...It keeps the piston itself from wearing and getting stuck..

Tight fit aluminium inside of a copper tube tends to get VERY stuck when it wears...

Brian the brain wrote:Not only that...It keeps the piston itself from wearing and getting stuck..

Tight fit aluminium inside of a copper tube tends to get VERY stuck when it wears...

Now that you mention it, a little moisture, a little electrolyte from veggies, rancid oil, or fruit, and the resulting battery will corrode the parts together very quickly. O rings to prevent contact and provide space is highly recommended.

Good call brian, thanks.

The battery effect never occured to me..smart thinking there

..just wear, but anyways...it's a good idea to leave those nice O-rings..

Sparkie wrote:With the barrel being inside the chamber I don't know the volume and I can't work it out

Calculate the volume of the chamber without barrel in it:
pi*r*r*h
r being radius (inner diameter/2), h being length of chamber
Then calculate the volume that the barrel takes up, same formula, but using the outer diameter of the barrel.
Then subtract them:
Actual chamber volume = chamber V - barrel V

Neat gun! You should indeed move up that blowgun.

Brian the brain wrote:The battery effect never occured to me..smart thinking there

Shhh don't say that! Pretend that that was what you were trying to say, and that its why you are named Brian the Brain!

Thanks guys.

POLAND_SPUD wrote:forget about shrader valves... buy a male quick connect fitting and put it instead of the nozzle on the blowgun (it has threads right ??)... in this way you could also get rid of that T (and greatly reduce pilot volume)

ohh.... you'll need a female qc one your air source as well, but that goes without saying

140/150 bar

that's a typo right ?? 50 bar would be more than you need

Yeh, sorry about that. Got a little exited. 140/150psi is correct(original post edited)




It never occurred to me to do that with a quick connect. Good thinking 99.

inonickname wrote:
Looks very good, the finish on the piston seems slightly rough but I bet it works very well with the rings!

If you don't want removing the air source to pilot your gun you could add a check valve or ball valve behind it, or use an attachment that leaks no air, such as a shock pump.



Good job

The piston is actually a plug left over from when he poured his moulds.
He melts aluminium and makes stuff with it.
The plug wasn't perfect but I am not complaining

Later on I will set up something for a permanent connection but at the moment I am just happy to play with it.

mark.f wrote:Blowguns will handle flow in either direction. I've used them either way many times.

As for your piston-piloting-dilemma, I would install a check valve before the schrader valve. A schrader closes at a speed that is a function of how quickly you can disconnect it. A check valve is already closed when it comes time to unhook your air source (both the sides have equal pressure), so there's no air loss.

One can be made in a pinch, but you should be able to find a small one somewhere.

Also, that piston is looking good, but how does air equalize through or around it?

I am trying to keep it as simple as possible. However to truly test it's abilities I may have to put a check valve in it.

About the piston.....hmmmm....what can I say. only finished it yesterday arvo and I had to try it. I will be drilling an equalisation hole in it sometime but for last nights tests I cut a bit out of the o ring and it is working well.

jackssmirkingrevenge wrote:
Good point, I would have the piston be an exact fit and remove the o-rings alltogether - no equalistation problems and much less friction.

I originally had some polyurethane rod which I wanted him to turn up for some o rings.
I didn't know he had that aluminium there till we were going to do the lathe work.
After we cleaned the aluminium up we had to use o ring and besides it looks way cooler this way

Technician1002 wrote:
Floating rings work well. A calibrated bleed port in the piston is easier to adjust than piston fit.

Never thought about making the bleed port adjustable.
I was going to start with a small hole and keep making it larger till it works.

Brian the brain wrote:Not only that...It keeps the piston itself from wearing and getting stuck..

Tight fit aluminium inside of a copper tube tends to get VERY stuck when it wears...

I would use o ring regardless. It makes for a better seal I would think.

Technician1002 wrote:
Now that you mention it, a little moisture, a little electrolyte from veggies, rancid oil, or fruit, and the resulting battery will corrode the parts together very quickly. O rings to prevent contact and provide space is highly recommended.

Good call brian, thanks.

What do you guys fire in your air cannons? sounds like a salad to me

psycix wrote:

Sparkie wrote:With the barrel being inside the chamber I don't know the volume and I can't work it out

Calculate the volume of the chamber without barrel in it:
pi*r*r*h
r being radius (inner diameter/2), h being length of chamber
Then calculate the volume that the barrel takes up, same formula, but using the outer diameter of the barrel.
Then subtract them:
Actual chamber volume = chamber V - barrel V

Neat gun! You should indeed move up that blowgun.

That looks suspiciously like a mathematical equation That means having to work something out....Aaaah...my poor brain......it's melting.....melting I tells you.


Sorry for the dramatics but maths was never my strong suit



Thanks for all the replies.
Now if only I could find some decent ammo. Well of to the ammo ideas thread for another look