A: Avoid one with a leaky valve, or one so stiff it takes a pipe wrench handled by Hercules himself to open and close the damn thing….

One other consideration with tanks and refilling them or exchanging them, whether they’re filled with oxygen or acetylene, is the issue of pressure-testing them. In most areas, tanks are usually required to be tested, and to have passed that test before they can be refilled. Not sure if this varies by location, but certainly it might by country. But in most cases in the U.S., if you take a tank in for refilling, and it’s past the expiration date from the last test, you might find the company unwilling to accept it for exchange, or to refill it without charging you for the pressure test. If the tank originally came from that firm, they will usually, but not always, waive that consideration, since they’d have to do the testing anyway, had the tank been returned just before the expiration date (the test dates are stamped into the tanks).

This, by the way, is true whether the tank is one you bought new, or one you got as an exchange. If you use the gas slowly enough that you’re likely to have that tank around for a longer time than the average welding shop might, then it would pay you, when exchanging the tank, to specifically request a tank that has long enough remaining since its last test so as to not cause trouble when it needs to be exchanged again. That request will often get you a somewhat newer tank, in my experience. If you specifically try to retain the exact tank you bought new (almost always difficult to do), then you also might find yourself being held responsible for the cost of pressure testing them now and then when getting them refilled.