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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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Do-it-yourself hydro testing?

Unread postAuthor: High-PSI » Mon Nov 14, 2011 4:30 pm

Hey Guys,

I am moving to higher pressure on my cannons (from 200 to 400psi) and I have a question;

I have a small Cannondale shock pump on order (I am a bike guy at heart) that is good to 600 psi. I am thinking it would be a good idea to do my own hydro testing of my tanks using this pump (filling the tank with water, then pressurizing the last tiny amount with air). If it is safe to 600 psi, then the 400 psi I will be running should be fine.

Thoughts?

Matt
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Unread postAuthor: Gun Freak » Mon Nov 14, 2011 4:41 pm

600 psi from a shock pump is unheard of, got a link? Definitely that method is fine, that's how hydro testing is done.
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Unread postAuthor: warhead052 » Mon Nov 14, 2011 4:47 pm

Gun Freak wrote:600 psi from a shock pump is unheard of, got a link


Google has heard of it.

I would say its possible, but it might take a little while to pump it up depending on the size of your chamber.
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Last edited by warhead052 on Mon Nov 14, 2011 4:51 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Mon Nov 14, 2011 4:49 pm

Gun Freak wrote:600 psi from a shock pump is unheard of, got a link?


Just because the gauges go up to 300-400 psi, doesn't mean you can't take them further with brute force ;)

Thoughts?


Does it have to be water? Think corrosion.
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Unread postAuthor: High-PSI » Mon Nov 14, 2011 4:52 pm

The pump is, indeed, able to reach 600 psi. That is what some new shocks are rated for. :)

http://www.google.com/url?sa=t&rct=j&q= ... 0xJ4iEQWCQ

The tanks all get wet inside anyway form condensation after each firing. I remove a drain plug to drain the tank, then shoot WD40 into the tank after each day of use. It is easy to see inside for inspection. The tank is clean inside.

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Unread postAuthor: Gun Freak » Mon Nov 14, 2011 5:01 pm

I beg your pardon, nice pump. Seems like you got it all under control. Should work fine.
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Unread postAuthor: MrCrowley » Mon Nov 14, 2011 6:26 pm

warhead052 wrote:it might take a little while to pump it up depending on the size of your chamber.

Fill it with more water? :wink:

Sounds like a plan, let us know how it goes.
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Unread postAuthor: High-PSI » Mon Nov 14, 2011 6:35 pm

MrCrowley wrote:
warhead052 wrote:it might take a little while to pump it up depending on the size of your chamber.

Fill it with more water? :wink:

Sounds like a plan, let us know how it goes.


Or how it blows? :D

My tank is DOM (drawn over mandrel) seamless steel tube that is 6 inch OD. The closest I can find on-line is sch 40 6 inch pipe. That pipe is 6.6 inch diameter and .26" wall thickness. My tank is .100" wall with a true size of 6 inches. Sch 10 tube would be roughly the same wall thickness as my tank. I cannot find pressure rating for 6 inch sch 10 steel pipe. However, I have found that halving schedule sizes drops PSI rating by about 40%. The sch 40 six inch pipe has a working rating of 1210 psi. that works out to be roughly 400 psi for sch 10 (which is roughly what I am running). Burst rating is about double that number. I know that is a very rough calculation. But, it should be somewhat reliable. However, my tank is welded together. I would like to think I am a good welder. However, stress concentrations could make the tank fail at a weld. We shall see. If it holds 600 psi for a few hours (assuming my fittings do not leak), then it should be very safe at 400 psi.

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Unread postAuthor: Technician1002 » Mon Nov 14, 2011 7:18 pm

Danger Will Robinson, Danger

Because air is compressible it can store lots if energy and the rapid release of the energy is dangerous. It will take lots of work to add air to the chamber and it is this energy when released rapidly that is so dangerous.

Always hydrotest with just water. For high pressure a small bore positive displacement hand pump is recommended. A very cheap source of this high pressure low volume pump with a standard 1/8th inch pipe thread fitting can be easly located at any hardware store or auto parts store.

Typical working pressure is 3000 PSI. Use a gauge.

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Unread postAuthor: mark.f » Mon Nov 14, 2011 8:29 pm

Technician1002 wrote:Image


For those who've been around a while, this is exactly how plasticex009 pressure tested launchers. I believe he substituted grease for dish soap (or maybe oil... I can't recall) to save on cash.
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Unread postAuthor: Insomniac » Mon Nov 14, 2011 8:57 pm

@Tech,

For small-ish launchers with chambers of maybe a litre or two capacity... I don't see the harm in hydro-testing by filling with water and adding a small amount of air. Sure, it's not as safe as the purely liquid method, but the amount of air we are talking is quite small provided all bubbles are eliminated and hose lengths are kept to a minimum. The water rocket crowd have been using this method for eons and while there is a bit of a release upon rupture, it's pretty tame. Just don't hold the launcher and use eye and ear protection and there's little that could happen.
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Unread postAuthor: Fnord » Mon Nov 14, 2011 10:29 pm

Although using a small amount of air isn't dangerous, it could cause other problems.
Mainly, it's compressible, and it takes time to reach that pressure even in small volumes. You'll probably want the chamber pressure to rise quite quickly when pumping, so any "lag" in pressure increase will be immediately identifiable as material deformation. With air you may overshoot the yield pressure without knowing it.

Anyway, I don't have much experience here, but this is what seems logical to me.
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Unread postAuthor: D_Hall » Tue Nov 15, 2011 12:35 am

Gun Freak wrote:600 psi from a shock pump is unheard of, got a link? Definitely that method is fine, that's how hydro testing is done.

No, that (using an air pump...even for the last tiny bit) is NOT how hydro testing is done.

As mentioned above... Industry practice for small volumes is to use a grease gun. Honey makes a good substitute media, by the way. It's thick so it goes through the gun like it's supposed to, but being water soluble it cleans up easy. I suppose corn syrup would work too.

And simply as a point of interest: For larger chambers, a pressure washer is the tool of choice.
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Unread postAuthor: Mr.Tallahassee » Tue Nov 15, 2011 12:44 am

Hydro testing is putting an incompressible fluid into a high ratio hydraulic pump. It uses the same principles as a common hydraulic jack to transfer power. It's that "incompressible" fluid that allows you to lift 2 or 3 ton vehicles with minimal effort on your part. That's why its called hydro testing. It's just a bad idea to use an air pump because air compresses.
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Unread postAuthor: mark.f » Tue Nov 15, 2011 7:32 am

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