I've been given a dive tank that has a 'J' valve on it. Do they still make this kind of tank/valve?

Question

...and could I resell something like this if I decide to get a newer tank?

Answer 1

No. No one uses J valves anymore if they can help it in recreational diving. You can replace that J with a K valve easily enough. The K valves only cost about 40 bucks installed. If you decided to sell the tank as is, the new owner would just replace that J valve and would probably consider that cost in the price they offer you as it's a liability ( reduces the resale value of the tank).

The reason why no one uses those J valves anymore is BECAUSE of that reserve feature. The tank can be mishandled or you can bump into something while submerged and knock the valve into an unexpected position, either reserve on or off. If you expect the reserve to cut out and warn you you're on your last 500 psi and it doesn't, because it's been flipped, you're going to get blue and bug eyed pretty quickly and wonder where all your air went.

J valves were around before it was common practice to put a pressure gauge on consoles and their sole purpose was to inform the diver they were down to 500 psi. Totally unnecessary now and also a potential failure point. You have a console to read, that's more reliable and doesn't just let you know if you're down to 500 psi, but let's you constantly know your air state. As an aside here, you'll be hard pressed to find a modern BC that will accommodate the reserve rod.

Lastly..a 500 psi reserve is not what's taught anymore. Rule of thirds is and since an alum 80 holds 3,000 psi you should be surfacing with more than 500.

If anything, those J valves will try to kill you. One of mine did and the reason why all my tanks were switched over to K's. Sometimes you just can't reach around to flip that valve and mine had decided to kick out  during a deco.

Answer 2

USN still TEACHES on j-valve's  K valves taought as well... but we're all told K= kill, because it doesn't leave you a reserve supply