I have several 20 pound cylinders that I would like to use as storage tanks for a light duty air compressor which currently uses no tank. Questions: #1 How much pressure can a cylinder take?
Question #2 Is there a kit to retrofit the cylinder to store air? If yes, where can I obtain. Do not need a pressure switch-already have, but what to use for input and output connectors... Thanks, Jim in MD
NAPA used to sell a conversion kit to make that type tank into an air caddy. I have been using one made like that for 20 years without any problems. I will have to replace the hose soon, but outside of that, the tank still holds air and is usually stored with some air under pressure.
I've never heard of double-walled tanks either, but I wouldn't use propane tanks because of internal moisture and rust. All air tank have a drain valve in a low spot to drain off condensation. I presume that they are either coated or are thick enough to begin with to handle the rust created by the moisture. Propane tanks don't have drain valves and may not be designed to deal with water/wet air. It's not worth a trip to the emergency room to find out.
It will work fine, and LP tanks are rated for around 300psi, If I remember correctly. I used a 100 gallon tank for 10 years or more, by tapping a water drain hole into the bottom in 1/8 NPT, after filling the tank with water and inverting it to drill. The valve on top was a pipe thread already, and accepted standard fittings. Include a pressure relief valve and you'll be set to go. The tank can tie most anywhere into the air piping you may already have, and can be valved off if you only need small amounts of air from your existing tank(s) /compressor.
I also can tell you that my Sears compressor tank isn't double-walled, and my $89.00 HF compressor sure as HELL isn't double-walled, nor do I have as much faith in it as I would have in a converted propane tank.
A valid point, but you could braze on a fitting for a drain valve or simply mount the tank upside-down and add a moisture trap downstream. (Do NOT braze on any propane tank unless you really know what you are doing, have taken all precautions (such as filling the tank with water), have shredded this message, and promise not to sue me)
The biggest problem with converting a propane tank to an air tank might be the residual odor.
I also once made a really stout safety gas can out of one.
Scavenge a connector from an old gas grill - the "output" is male 1/4" NPT. To that you can connect anything that's convenient for your use. I have a quick-disconnect fitting on my portable tank (input is female
1/4 NPT - connects directly to the grill fitting).
You absolutely do need to use the pressure switch to control the compressor.
The mercaptan odor will never go away on its own. Rinsing with a little bleach almost totally removes it. It's easier to rinse with the valve off, but not at all necessary (I don't remove it).
Install the tanks upside down to allow water purging.
The 20# tanks are about 5 gallons. Even 3 of them is not much air storage, but the price _is_ right.
The valves on the tanks I've seen have a mechanism to limit flow if there is a sudden demand for a large flow. This is to limit the flow if a hose fails. The valves connected to the tank via a standard 3/4"NPT pipe thread so you can remove the valve and replace it with something more appropriate to your application.
AFAIK these are the valves that came into use in the mid nineties, they are identified by the coarse, external, Acme type, RH thread for connection to the regulator. They will accept the older, internal LH thread type connector, but the free flow limiting feature is disabled by this connection. I have not verified this bypass type feature, but I have used the older type connectors with no problem. Older tanks which I use as air pigs keep their valves and use a christmas tree with the old LH thread connector feeding a manifold with gauge, female quick connect, tire type valve stem, and a 1/4" pipe thread ball valve. As far as the Mercaptan odour goes, I find that a few purges of clean air over several weeks reduce it to an acceptable level. Gerry :-)} London, Canada
Nope. I have some outdated ones with the old style valves that have this feature. The one I use to top up tires has one. I have to squeeze the trigger slowly to keep it from triggering. It will give lots of flow but not suddenly.