Fill Station on Wheels?

[Doc Harry]

Background

That's a fantastic article that helped me a lot when I was getting my fill station up-and running.

 

[Akyla]

I run my whole compressor system in an enclosed trailer to include the nitrox membrane and cascades for both air and 40%. I use a marine grade power cord and pull in 220 60 amps at the dock behind the boat and at my house. That is enough for a k14 and the fans I have set up to boost air flow for cooling, lighting, etc. I have more in this trailer than most small dive shops do. It works great but you need a heavy duty trailer with extra supports in walls to securely hold the bottles and use the transport caps on the cylinders if you are going to tow it around, just in case.

 

[AaronRiot]

Fill station on wheels, what am I missing?

Deep fryer, grill, loaded fridge/freezer, cash register.





-seriously though, the travelling fill station is a great idea!

 

[totalloser]

One note on the background. I *think* there might be a misconception in the article. I'm somewhat new to the hardware involved, but I believe the assumption that the burst disc functioning protects you from the lack of hydrotest is incorrect. As I understand it the burst disc prevents over-pressurization of the tank. The hydrotest is to check that the tank material has not been stressed past it's yield strength.

In short, the concept is that a hydrotest verifies the tank is in good shape regardless of the burst disc. A bad tank in theory could rupture regardless of the burst disc. If it's anything like a valve getting knocked off, probably remarkable dangerous, hence hydrotests. (?) Maybe I'm reading it wrong- see above disclaimer of experience level

 

[Doc Harry]

One note on the background. I *think* there might be a misconception in the article. I'm somewhat new to the hardware involved, but I believe the assumption that the burst disc functioning protects you from the lack of hydrotest is incorrect. As I understand it the burst disc prevents over-pressurization of the tank. The hydrotest is to check that the tank material has not been stressed past it's yield strength.

In short, the concept is that a hydrotest verifies the tank is in good shape regardless of the burst disc. A bad tank in theory could rupture regardless of the burst disc. If it's anything like a valve getting knocked off, probably remarkable dangerous, hence hydrotests. (?) Maybe I'm reading it wrong- see above disclaimer of experience level

You are correct, the author has a misconception of the role of the burst disk and its relation to hydro. The burst disk has a function that is unrelated to hydro.

The burst disk is designed to prevent cylinder failure from over-pressurization.

Hydro is designed to test whether or not a cylinder is still within the elastic expansion-contraction limits of the alloy.

Yield strength is indirectly related to hydro, as I understand it. Yield strength testing (i.e., intentionally over-pressurizing a cylinder until it fails) is done by the manufacturer in the R&D phase to determine the final alloy composition and thickness in the final production model. Through this testing comes the allowable expansion limits for hydrostatic testing. That's my understanding.

The author of that article made the incorrect assumption that a cylinder that is out of hydro would be protected from exploding by the burst disk. Yes, it would, but for the wrong reasons. A burst disk will prevent the cylinder from exploding if the cylinder is over-pressurized past the limits of the burst disk. In the case cited in the article, the burst disks were rated to 6,200 p.s.i.

However, a cylinder that is fatigued to the point where it will no longer pass hydro can fail catastrophically (i.e., explode) at pressures well below the burst disk rating. In fact, these cylinders can even explode at pressures well below the rated fill pressure of the cylinder.

Many of the scuba cylinders that have exploded did so during the filling process at pressures well below the rated fill pressure of the cylinder. Did a burst disk prevent these cylinders from exploding?

 

[unclejoe11101]

2 thoughts, laying your tanks down would help lower the center of gravity, maybe under a false floor ?and vent,vent,vent.Heat out,fresh air in,exhaust out, maybe the sides could open like a snack trailer?Wishing you the best of luck Joe

 

[frogman62]

Laying the tanks down will certainly lower the center of gravity. If the tanks are subject to wide temperature swings you could get some water condensation in the tank. The water will run down on the lower side of the tank against the side wall, which is relatively thin compared to the bottom of the tank, creating the potential for a long rust line. --- "NOT A GOOD THING" I'd rather drive safely with a high center of gravity than have a tank split open 2-4 years from now.
Jim Shelden