SpudFiles

I have been wanting to build a large pneumatic that has a 2 gallon + capacity that is sill hand held. The problem I see is what to use for a tank because the Homedepot and Lowe's near me only carry 2" pressure rated pipe at the largest. So I have a couple of ideas for alternative tanks. One is the garden sprayer tanks for weeds like this one:
http://www.pet-dog-cat-supply-store.com ... 6a0183.jpg
These things may look weak, but I got a chance to see and feel one and they are actually pretty rigid for having such a large diameter. I could barely squish it a quarter inch with my arms.

My other Idea would be one of those old copper fire extinguishers. This would perfect because you could solder everything together instead of epoxy to assure a strong bond. With a tank like this:
http://www.thechattanoogaauctionhouse.c ... ExtM08.JPG

You could make a cannon similar to Technician's propane tank cannon, but instead of brazing you could solder it.

Do you guys think that these tanks could work?

Out of those two I would buy the fire extinguisher, but you could always get large diameter pressure rated pvc pipe/fittings on sprinkler.com.

Use old propane tanks. The 11 Lb ones are about 2.5 gallon, right in the size you requested. The 20 Lb tanks are about 5 gallon. The bummer is they are only fitted with a 3/4 pipe thread.

The old style tanks are often tossed and can be had for FREE. The cost of a new valve and recertification is about $50. I was going to have the small tank below fitted with the new valve. They wanted $30 to replace the valve and $20 to certify it. A new tank certification is good for 12 years from date of manufacture. An old tank certification is only good for 5 years.

In my book a FREE tank is the right price.

I believe the pressure relief valve on propane tanks is set to 305 PSI.
EDIT; Found some info on Propane relief valves. The cylinder service pressure of 240 PSI is reached with a temperature of 124 degrees F. The relief valve has a minimum setpoint, so a warm cylinder doesn't vent too soon. The DOT minimum set point is 360 PSI. Liquid propane reaches that pressure at 158 degrees F. Never leave a propane tank in a car on a warm day. It may overheat and vent. I am still looking for the maximum setpoint.

Found this gem..
http://www.propanecouncil.org/uploadedFiles/
GRR posting the entire link blanked my post..

The best I can do to get you there is use this Google search and use the Propane Council PDF page. It has the info.
http://www.google.com/#hl=en&q=Propane+ ... EE02fthf5k
Propane cylinders have a service pressure of 240 PSI and a minimum burst pressure of 960 PSI a 4X safety margin as required by DOT.
Forget buying a wimpy air tank rated for only 125 or 150 PSI.

You could make a cannon similar to Technician's propane tank cannon, but instead of brazing you could solder it.

I've never tried to silver bearing solder a steel tank. I'll have to try it for those without welding torches for brazing.

These tanks are the start of my next two launchers. 3 inch and 4 inch.
The large tank is either a 7 or 10 gallon. I'm not sure which. I'll check it later.

EDIT Update. I checked the volume of the large tank. It has a WC (Water Capacity) of 66 Lbs of water which is 7.9 Gallons. At 231 cubic inches per gallon, that would be about 1825 cubic inches. Nice size tank for the 4 inch.

I once tried to remove the valve from a propane tank and I couldn't do it.

Hints?

When I was talking about soldering the barrel to the tank, I was referring to the copper fire extinguisher (that my friend happens to have 8) ) and using regular old solder. If silver bearing solder works with steel that may be another good option if I come across a steel tank of some kind.

Is the garden sprayer idea any good? Those things are designed for pressure. If I reinforced it with fiberglass cloth and epoxy do you think it could be used safely?

Thanks

auxiliary wrote:When I was talking about soldering the barrel to the tank, I was referring to the copper fire extinguisher (that my friend happens to have 8) ) and using regular old solder. If silver bearing solder works with steel that may be another good option if I come across a steel tank of some kind.

Is the garden sprayer idea any good? Those things are designed for pressure. If I reinforced it with fiberglass cloth and epoxy do you think it could be used safely?

Thanks

Electrical solder is for electrical connections. It is not very strong. Plumbing solder is better as it is for connections under pressure. Regular old solder can be either lead free plumbing solder or lead and tin solder. Which regular old solder needs to be specified.

The garden sprayer is OK if you wish to stick to the original pressure it used. Most have a fairly large diameter pump and room for only one hand on the handle, so most are not designed for over 60 PSI. Keep that in mind. Most are used at between 20-30 PSI.

For safety, I would start with a tank rated for above the pressure you wish to use. For example the t shirt cannon. It started with a freon tank. After cutting and brazing we limited it to less than 1/2 the original pressure.

boyntonstu wrote:I once tried to remove the valve from a propane tank and I couldn't do it.

Hints?

They are very tight. A padded chain vise if you have one and a long 1-1/8th open end wrench is preferred. Don't use an adjustable. It will break.

The joint compound sets up. For a stuck valve, I heat the valve until it just discolors to soften the sealant. The joint compund tends to set up with age. Then I can get them out. I had to heat the valve on the small yellow tank to get it out. With the plugs removed and guts taken out, I got a little extra flame as the propane expanded from heating. With no oxygen in the tank it didn't flame into the tank, but went out after heating.

Do not do this with a tank that has had the valve left open. Air in the tank may leave an explosive mixture.

I used a nail bar in one of the handle slots and against the valve shank to hold the tank while turning the valve with the wrench. An yes, they are VERY TIGHT.

auxiliary wrote:Is the garden sprayer idea any good? Those things are designed for pressure. If I reinforced it with fiberglass cloth and epoxy do you think it could be used safely?

Rummaging about on the web it looks like tech is correct, those plastic sprayers have pop-off safety valves rated at about 30 PSI (though they are wildly inaccurate). You might find one as high as 60 PSI. That seems a bit low for a decent pneumatic.

I wouldn't trust fiberglass to reinforce a plastic tank. The problem is that you have to get 100% of the tank reinforced, including the cap and pump assembly. If you only get 99% of the surface reinforced you've got'a bomb sitting next to you.

I meant plumbing solder when I said "regular old solder". I looked around my garage and found some silver bearing solder and tried soldering two short segments of steel pipe together by their sides so there was little surface area. I managed to get the solder to flow and when it cooled, I tried to wrench it apart with my hands (didn't work) and then took a hammer to it. With a couple firm taps it broke. If silver bearing solder has this kind of strength with such little surface area, I thing it could be used for securing a steel pipe inside a propane tank (with beveled edges of course).

I think what you're actually looking for there is a proper weld...

The kind of force exerted by your hands on two short bits of pipe side by side is nothing to the force a long lever in the form of a barrel will put on the join.

auxiliary wrote:I meant plumbing solder when I said "regular old solder". I looked around my garage and found some silver bearing solder and tried soldering two short segments of steel pipe together by their sides so there was little surface area. I managed to get the solder to flow and when it cooled, I tried to wrench it apart with my hands (didn't work) and then took a hammer to it. With a couple firm taps it broke. If silver bearing solder has this kind of strength with such little surface area, I thing it could be used for securing a steel pipe inside a propane tank (with beveled edges of course).

I had to know, so I had to test. Will plumbing solder adhere to steel? To test I picked a spot on the handle and burnt off the paint and gently scraped it with a stick. Let's see if flux will clean it. It didn't work very well, but some solder stuck, so it looks promising.

I used a file as I didn't have sandpaper handy and did a quick job of removing the years of crud. Fluxed it and tried again.. Much better. It should work well with plumbing lead free solder and flux or silver bearing solder. Clean is required.

I also took a picture of the flux and solder used for this test and one of the old valves. I bent the outlet reefing on it before it came loose.

Hotwired wrote:I think what you're actually looking for there is a proper weld...

The kind of force exerted by your hands on two short bits of pipe side by side is nothing to the force a long lever in the form of a barrel will put on the join.

This would be true if the force did act on the joint. With long barrels the support is often on the barrel itself with the tank hanging off the back. In the marshmallow cannon, most of the support is on the barrel at the front as the rear hand only has the trigger knob to grip. I designed it that way to prevent breaking barrels and connectors from long barrel torque.

Leverage would be a problem if the tank was bolted down. As a hand held, it's not a problem. I would expect to tear out the plastic threads on the screw on the plastic barrel before breaking a solder joint.

EDIT Update. I checked the volume of the large tank. It has a WC (Water Capacity) of 66 Lbs of water which is 7.9 Gallons. At 231 cubic inches per gallon, that would be about 1825 cubic inches. Nice size tank for the 4 inch.

do you think lead-tin plumbing solder would stick to steel?

i hate lead/tin i would get some tin/antimony if i tried anything

spudtyrrant wrote:i hate lead/tin i would get some tin/antimony if i tried anything

I just looked up the MSDS on the lead free solder. By weight it is >90% Tin, <5% copper, <2% silver, and < 2% Antimony.