Tank ?s

[3KgtVR4]

Hello all, my name is Brian Walls and I'm new to the forums. I'm PADI certified, but have only been a couple time and haven't been in many years. Was wanting to take a refresher and get back into diving and had a non diving scuba idea. Hope this isn't too much off topic, but here goes...I'm a commercial plumber and we have to test all of our underground plumbing with 5psi of air, not much psi but it can be a huge volume and take a while with an air compressor. I was thinking about using a scuba tank to speed up the fill. Here's my questions 1)can I regulate a scuba tank down to 5 psi with the standard regulator on a tank or will I need two? 2)What type of threads do they have on the output of the regulators? 3)And this one might be a tough one. I want to see how many ft of pipe I can get out of one tank. From what I come up if you had a 100cu ft tank at 3300psi it should be 22,548 cu ft of air at atmospheric pressure(3314.7psia x 100cu ft / 14.7psia). And 1' of 4" pipe at 5psi would be 0.1169 cu ft of air at atmospheric pressure(19.7psi x .08729 cu ft / 14.7psia). That would be 204,981ft of 4" pipe per tank. This dosnt sound right to me, I think I could be totally off. One thing I'm stumped on is where the 100cu ft on the tank comes from? Is this number the total cu ft of the tank at atmospheric pressure? When I do the math for cu ft on a 1' piece of 4" pipe its only .087 cu ft and just a couple feet of 4" pipe should match the inside volume of a scuba tank. Sorry for the novel and thanks for any help,
Brian Walls

 

[elan]

Brian a 100ft tank will contain 100ft measured at 1 ata. The internal volume of the tank at 3300 psi is in a range of 12 litres which is roughly between 1/2 and 1/3 of a cubic ft. So the whole tank would contain around 2-3 m3 of gas which i really not that much.

My best dive buddy is a comercial plumber serving metro toronto area and knowing all the physics and tank sizes he still pulls the compressor around with his truck

 

[herman]

Your math is so far off because a 100 cf tanks has roughly 100 cf in it at full pressure, not 22,500 cf as you assumed. Without doing the math, your results are off by a factor of 100. There are some more math assumptions but that is the major one.

As for retuning a reg to a a 5psi IP, I have seen a few diaphgarm regs that would but they are rare, odds are you will need to use 2 regs in series to get the reduction you want. A welding regulator would be a better choice. All in all, a small air compressor with a few gallon tank as backup is a much easier option...and you don't have to find a scuba shop to refill it.

 

[hroark2112]

Don't waste a good scuba tank on crappy pipe

im a plumbing contractor in NC. I've used a nitrogen tank & regulator setup before for testing water lines (they won't let us test PVC with air here). I always got the tanks & regulators from the welding supply shops.

 

[HIGHwing]

Brian a 100ft tank will contain 100ft measured at 1 ata.

Not even the metric system can save that math.