Air gauge just tells you why it blew, doesn't protect against it. Can you guarantee that the walls of the pressure vessle have absolutly no internal corrosion? A few corrosion pits will derate the vessle by half or more. Vessles in industrial service must be checked regularly and certified for service. I'm not concerned about the pop off valve - on the proper type vessle, it is an appropriate protection. However, the energy stored in pressurized gas is MANY times that stored in pressurized water. If a 120psig water heater bursts, a seam splits and the water runs out. If the same vessle bursts from gas pressure, it will take out the whole building, maybe the next building over and the vessle will be found half a mile away if it is found at all. I have seen the result of an air reciever vessle bursting and it is very sobering. Air tanks cost a lot more than water tanks of the same pressure rating for a reason. Don't want to rain on your parade but that isn't a good place to economize.
Check with welding supply store, maybe Lowe's can get you one, or Harbor Freight probably can supply you one at a discount price.
[ May 01, 2003: Message edited by: firstname.lastname@example.org ]</p>