Different size tank pressure

[upper_tanker]

Good morning,

A co-worker and I were just talking about O2 and Air tanks and were both wondering about two different size tanks that were connected to the same output line. Would this cause an issue with the smaller tank being over-pressurized by the larger tank? If we got two "new" full tanks and connected them inline to one output line, would this be OK? Or would there be a chance of the smaller one blowing up? Obviously, neither of us know much about gasses and their containers.

 

[cvairwerks]

Assuming no check valves, the tanks will equalize at a common pressure. Now jacking with an air tank and connecting it to a tank of O2, is a whole ‘nother story. I wouldn’t want to be within a mile of someone doing that. Connection of different volume tanks is done all the time, but the pressures involved must be within the working pressure limits of the lowest rated tank. An over pressure is not fun to be around. BTDT when some idiots tried to pressure check an O2 accumulator that was only rated for 250 PSIG and they hit it with over 500 PSIG of oxygen.

 

[upper_tanker]

Assuming no check valves, the tanks will equalize at a common pressure. Now jacking with an air tank and connecting it to a tank of O2, is a whole ‘nother story. I wouldn’t want to be within a mile of someone doing that. Connection of different volume tanks is done all the time, but the pressures involved must be within the working pressure limits of the lowest rated tank. An over pressure is not fun to be around. BTDT when some idiots tried to pressure check an O2 accumulator that was only rated for 250 PSIG and they hit it with over 500 PSIG of oxygen.

In our case, we often get mismatched size tanks that usually come with 2500 and 2800 lbs of gas (I'm not sure if that's the right terminology, these look like regular auto shop O2/Acetylene tanks). Again, not sure if this helps or even makes sense due to my lack of knowledge about different gases and tanks. They are about 6" difference in height. Obviously we are connecting two O2 tanks and two air tanks together, NOT mixing gasses so there's no worry about that.

 

[cvairwerks]

Typically, unless you are using the tanks in a cascade layout, you run one til it’s at minimum, then swap to a full one. In a cascade, each tank can feed the system with it’s own regulator and maintain the desired line pressure until all open tanks are empty.

 

[upper_tanker]

For our job, we have two tanks running to a single line that runs over to two workstations where it T's off to each one. Two techs usually go through two tanks (of either gas) in 2-3 days. Usually, we will open the larger tank first and use it until it gets down to around the amount of volume as the smaller tank, and then crack them both open. I guess it's just being lazy, but it'd be nice to know whether or not opening two completely full different sized tanks at the same time would matter or not from a safety perspective.

The tanks themselves do not have regulators. The only regulators are at each workstation, each having one for O2 and one for air.

 

[cvairwerks]

The tanks themselves do not have regulators. The only regulators are at each workstation, each having one for O2 and one for air.

In this case, I would open one tank on the line and run on it until near empty and then close it off and open the other.

Volume is not the problem, but rather, pressure. When having connected and you open one with higher pressure than another, it will raise the pressure in the low one. Depending on how much differential there is and how fast you open the valves, you can induce some decent heating of the gas in the lower pressure tank. When we fill the bail out bottles on the ejection seats, we charge the bottle at such a rate that we only get a 20-30 degree rise in the bottle temp. The gas temp is considerable more than that. We then have to allow the bottle to cool to within a certain amount of the original temp before removing from the charging rack. The faster you fill, the higher and quicker the temp rise. From the physics side of things, look up the Combined Gas Law.

 

[upper_tanker]

In this case, I would open one tank on the line and run on it until near empty and then close it off and open the other.

Volume is not the problem, but rather, pressure. When having connected and you open one with higher pressure than another, it will raise the pressure in the low one. Depending on how much differential there is and how fast you open the valves, you can induce some decent heating of the gas in the lower pressure tank. When we fill the bail out bottles on the ejection seats, we charge the bottle at such a rate that we only get a 20-30 degree rise in the bottle temp. The gas temp is considerable more than that. We then have to allow the bottle to cool to within a certain amount of the original temp before removing from the charging rack. The faster you fill, the higher and quicker the temp rise. From the physics side of things, look up the Combined Gas Law.

Thank you for all of your responses. I will definitely look up Combined Gas Law tonight. I figured we should just keep using the smaller tank first until it gets down to the same pressure as the large one, and I'm glad that somebody else confirmed it.