Compressor Question

If the tank is in good condition then it would work providing that it will have the necessary number of threaded openings for fittings. The threads might be different so machining adapters might be necessary. Do not drill more openings in the tank, use T fittings if you need more openings.
Try to make one of the openings act as a drain plug for condensation water. If that's not possible then make sure you can drain the water downstream.
A.B.
VW Golf Cart wrote:

Are thinking about a hot water HEATER tank or a hot water BOILER tank? They are quite different critters.
I certainly would not consider a used one for the project. They usually have enough accumulated corrosion to make them pretty weak.
Keep in mind that a failure in a hot water tank results in a small pressure leak and then just drips. The compressed air tank has a large amount of stored energy, they can fail catastrophically.
VW Golf Cart wrote:

I'd be inclined to agree.
Harold

No way. Air receivers are built a lot more stout than water heater tanks, because a water tank failure usually isn't catastrophic, and an air receiver usually is. Go look at film of a steam boiler explosion sometime, there's a whole lot of energy that wants to get out in a hurry - air isn't quite as nasty as steam, but it still goes BOOM!
I'd go locate a rated air receiver tank and add it in series with the existing unit, as in downstream. You could put a refrigerated air dryer unit between the two tanks and install a restrictor orifice or flow regulator at the drier input, so now you have a large reserve tank of dry air after the drier. (And the drier works better without having to supply flow surges past it's nominal capacity.)
-->--

Greetings and Salutations.
You can also play Russian Roulette with a .45. I had a client some years ago that did this. It blew up on him, and, put a bit chunk of shrapnel right through his stomach and out the back. Considering that he was called "Big John" for a good reason...this was pretty impressive. Get a real pressure tank for this. They are not that expensive. Regards Dave Mundt

Greetings and Salutations...
*snip* and JUST to clarify...the client did *not* play Russian Roulette with a .45. He WAS using a hot water heater as a pressure storage vessel, and, probably had it pumped up to about 150 lbs or so...what "SHOULD" have been safe. the problem with water heaters is that they are thinner than air pressure vessels, so when they rupture, they often rip apart. The heavier, air vessels, tend to get pin holes and hiss on down. Regards Dave Mundt