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Do-it-yourself hydro testing?

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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Unread postAuthor: High-PSI » Tue Nov 15, 2011 8:26 am

Yes, air is compressable, but 600 psi is still 600 psi no matter what medium you use. If there is virtually no air space inside the tank, the amount of energy stored is very small, indeed, so any rupture would be pitiful. I plan on filling the tank as much as is humanly possible. I have a drain hole at the bottom of my tank. I can fill it completely full, then pump air into it.

The shock pump is merely a convenient way to do this for a number of reasons;

#1 I already have the pump coming for my forks and shocks.

#2 It has its own guage, so no special settups required there.

#3 I have all fittings and what-not on hand right now for this.

But, if there is a specific problem with this method of pressure testing, I want to know so I can avoid any major issues.

Matt
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Unread postAuthor: mobile chernobyl » Tue Nov 15, 2011 8:30 am

I think all the specific problems and issues were brought up in the last 4 posts... you can choose whether or not to consider them though :wink:

I've personally hydrotested a few things. Some were my own welds for my hybrid, some were my welds for very large high pressure industrial water purification projects, and some were testing objects to failure (such as burst discs). I can confirm what the general "gist" of the last 4 posts said - using anything that is compressible will skew your perception of the results. The point of hydrotesting is not just merely pressurizing something and saying "ok it passed" but it's getting feedback on that pressure. With a incompressible fluid you get direct force feedback and you can easily tell when the object is undergoing elastic deformation, and when it's gone beyond that.

Do as you will, and if all your concerned about is "will ma vessel hold teh pressurez?" then your method is perfectly adequate... just don't hydrotest anything for anyone else though please. thanks!
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Unread postAuthor: High-PSI » Tue Nov 15, 2011 8:46 am

Ahh, OK, very good explanation! I understand what you are saying. I am a technical person. I like knowing the "Why" of things. This, now, makes perfect sense. I was not thinking about plastic deformation analysis. That is a good reason to do straight hydro testing.

I know where to get a grease gun, that is no problem. Now, what about a fluid pressure guage and anything else I might need?

Again, thanks for the proper explanation. The others were saying the same thing, in essence, but I did not understand them. :)

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Unread postAuthor: mobile chernobyl » Tue Nov 15, 2011 8:56 am

Glad I could clear it up... that 2 year "break" spent working before I started college has paid off with more applied knowledge in my field of study than I could ever have hoped for! :D

Air testing is suitable for a "leak test". My father works on projects involving safety equipment, and one of his recent ones was the entire rail system under new york city. They were testing a "dry" standpipe which is an emergency water pipe for fires. To test this, it involved pressurizing miles of pipes usually 4 inches in diameter or greater. They simply plugged up the feed end to a high output turbine compressor, pumped it up to 100psi and checked for leaking overnight during the down time.
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Unread postAuthor: High-PSI » Fri Dec 02, 2011 4:52 pm

OK, I decided to test my tank with my shock pump. I filled the tank completely with water. It was so full, the valve fitting was squirting as I tightened it down. :)

Anyway, I filled it and pressurized it to 625 psi. I left it for 10 minutes and drained the tank. Now it is at the powder-coater to be coated a nice semi-gloss black.

I am thrilled with this. Now I feel safe charging it to the 300 psi I have been aiming for. Heck, 400 psi doesn't seem that bad now that it has held over 600.

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Unread postAuthor: jackssmirkingrevenge » Sat Dec 03, 2011 12:14 am

High-PSI wrote:OK, I decided to test my tank with my shock pump.


Surprised you didn't use your new fridgy ;) good stuff though!
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Unread postAuthor: High-PSI » Sat Dec 03, 2011 7:14 am

I thought about it. But, that would have compressed the tiny amount of air in the line way too quickly. I did not want to purposely blow the tank. I just wanted to give it enough pressure to assure it would hold with 600+ psi.

I will purchase a grease gun to do 100% hydro testing on future tanks. But, I had just enough time to do this experiment before running to the powder-coater and I already had the tire pump, so I went this route for now.

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Unread postAuthor: POLAND_SPUD » Sat Dec 03, 2011 11:17 am

Surprised you didn't use your new fridgy
lol I can tell you've never had a fridge compressor :D

isn't it time to get one??
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 03, 2011 12:00 pm

POLAND_SPUD wrote:isn't it time to get one??


I have three by my feet as I type this, I have yet to rewire them but I also have a 300 bar SCUBA, so what's the point ;)
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Unread postAuthor: POLAND_SPUD » Sat Dec 03, 2011 12:43 pm

I also have a 300 bar SCUBA, so what's the point
you're limited to 850psi max... that's what you can achieve with a fridge compressor fed pressurised air... htough it'
s not that you acctually use 850 psi regularly

So a fridge compressor = cheaper pressurised air
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 03, 2011 1:14 pm

POLAND_SPUD wrote:So a fridge compressor = cheaper pressurised air


Since I'm mostly mucking around with hybrids these days €5 for an 8 litre SCUBA fill isn't too much of a drain on my bank account, in fact I can't remember when the last time I filled it was.

What would be interesting is seeing if one could be made to run off an automotive 12V supply...
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Unread postAuthor: POLAND_SPUD » Sat Dec 03, 2011 1:20 pm

AFAIK even the cheapeast inverters should be able to power it (wattage of most fridge compressors is 125W - 150W whereas even the cheapest inerters are rated to 500W or so)
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Unread postAuthor: High-PSI » Sat Dec 03, 2011 1:38 pm

I plan on running an inverter for field use.

I stumbled on an old scuba tank at a friend's house. I do not plan on having it filled by a scuba store, however. I would like to use it to fill with my fridge compressor. So, it will only be charged to 800 psi. The big issue now is a regulator that can deal with 800 psi that doesn't cost hundreds of dollars........

Oh, I fired my small 1/2 inch pipe cannon today with a 6 gram round at 500 psi. I also dry-fired it at 600 psi. I will comment on it and post youtube videos on that thread sometime today, when I get time to upload them.

I can tell you this, it was really LOUD and kicked pretty hard for a small bore. :D

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Unread postAuthor: Goats spudz » Sat Dec 03, 2011 5:45 pm

You will be there forever with a fridgy and you can hydro test up to 3000 psi with a grease gun
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Unread postAuthor: High-PSI » Sat Dec 03, 2011 6:07 pm

I do not care how long it takes to air it up. It will be used for airing up in the field when I do not want to bring the compressor along.

One thing, my big 2.5 gallon tank only takes 3 minutes to charge to 400 psi with my fridge compressor and a 75 psi precharge. So, filling the scuba tank should not take all day.

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