I doubt your garage compressor can make 2-3000psi
Absolutely this.
I recently got my hands on a used scuba tank and was wondering what kind of parts I would need to make it work for onboard air. What kind of regulator, fittings and anything else I might need? I have a 25 gallon compressor in my garage can I fill the scuba tank off of my compressor before trips out? It would be nice to be able to air up and down and run air tools if needed. Any input would be helpful. Thanks
What kind of tank is it? (size, material). 80cuft aluminum are the most common. What valve is on it too, DIN or yoke? (DIN = big hole with threads, yoke = face with small hole and o-ring. You'll need to know this to find out what regulator you'll need)
A scuba tank as Souske said can run between 2000psi-3500psi, depending on low, normal or high pressure builds, but most are usually 3kpsi. You're 150psi air compressor is not going to fill even a fraction of that tank.
Before you do anything with it, does the tank have all its certifications on it? A tank has to be hydrostatically tested every 5 years and approved by the DOT, as well as a visual inspection by a scuba shop every year. The hydro is stamped at the top of the tank near the neck, and will have a month, the symbols of the facility that tested it, and then the year. The Vis will have a sticker somewhere on the side of the tank, and it will have the year and month on it, and will usually say visual inspection. Make sure both of those are in date, otherwise a scuba shop (a reputable one at least) will not fill the tank for you. If the tank is aluminum from the 70's or 80's, throw it away now, it is useless to you. Also be aware that tanks can be sent out for hydro and be condemned, and you won't get them back.
As far as a regulator, you will need to get a 1st stage regulator from a scuba set up to regulate the pressure down from 3kpsi, to 100-200psi over ambient. Go and talk with a local scuba shop and talk with them about what you're doing. Almost all scuba shops will sell off their rental equipment for a discounted price at the end of the year, see if they have any left over. Also look on craigslist or ebay to see if anyone has anything available.
Since you won't actually need to breath off of it at depth, the cheapest 1st stage regulators are an unbalanced piston design. See if you can find those cheap anywhere. You'll need to plug all the ports (especially the HP port(s)), and then get some adapters to plug into the LP port, or more likely use a hose that comes with the regulator or that you can get fairly cheap at a shop.You'll probably also need a regular air regulator that you can get at home depot or similar to further be able to adjust the pressure.
I would also recommend finding out the correct way to bleed the regulator lines before trying to disconnect the regulator from the tank.
