Hydro testing?

[johncedarhill]

I am curious about the water that remains in the tanks after hydrotesting. How is it removed? Is it just drained or what. Before I invest in a tank which has a limited life I would like to find out as much about tanks etc as I can. Thinking about a 4500 psi job.

[NMCA_Ron]

John,

I am thinking that if you could apply suction to the tank for a period of about 30 minutes at 30 inches of vacuum - like with a pump they use to evacuate air conditioning units - you could remove ALL the moisture in the tank. Just remember to close the valve before you disconnect the vacuum source and don't open it until you fill it. This will keep any humidity from being drawn back into the tank. This is how we serviced our nitrous oxide cylinders and it works very well.

Ron

[3n00n]

http://www.diversmarket.com/repairs.asp

Hydrostatic Testing - Done every 5 years
After the V. I. P. and the Visual Plus inspections, the cylinder is filled with water. The cylinder is then submerged in a vat of water with a secured lid. All the air is purged out of the cylinder being tested and the vat it's submerged in. Next, the cylinder being tested is pressurized, using water pressure, to the D.O.T. specified directives. Normally this is 5/3 the working pressure of the cylinder (i.e. an aluminum 80 normally gets filled to 3000 psi and is hydro-statically tested to 5000 psi). When the cylinder is pressurized, it expands. The amount of expansion is measured through displacement in pipette tubes. When the pressure is released a second measurement is taken for permanent expansion results. If the permanent expansion is within limits the tank passes and kept in service. The tank is emptied of water, dried, stamped with the month, retesters I.D. Number, and year. The valve is installed, and the cylinder is filled and checked for leaks.

[kirby999]

Great information J , I didn't know that was how it was done. kirby

[johncedarhill]

Thanks. So must a tank be discarded after 15 years? A new tank is about twice the cost of one that is sold on yellow. I am also concerned about getting all of the fittings that are needed. I always seem to buy something and find out I need a whole bunch of other stuff. I think a regulator for 200 bar would be handy if not necessary. I got a used pump but the gage is broken etc. I think I could live with a pump but if I want to do more shooting I need a tank. THen basically I want more pcp's but I have all the stuff. A compressor--well if the life of it is longer than the tanks and I don't have to worry about hydro etc. maybe that is the way to go. I see where quotes on compressors have to be requested which suggests they are super expensive. I have to take a trip to the local rural Fire Dept. and see if I can get filled there--probably not.

[kirby999]

Just what I've heard , it may not be fact. A steel or aluminum tank is good until it fails a hydro, The wrapped tanks have expirations . I know the ones we used at work to hold CNG compressed natural gas ; had to be retired after so long.  kirby

This brings up a question: What about the PCP's tank itself? It gets filled to the same pressure as the scuba tank, does it have a lifespan? How safe is it considering it's never hydrostatically tested? Might be a good idea to discard and replace the tank on the PCP at around the same time as the scuba tank?

[kirby999]

Most manufacturers recommend an inspection and hydro ever so often.  Laws requirements(I think)   depends upon the size of the tank I believe. I know the Talon tanks are supposed to be checked and tested every 5 years  like scuba tanks and have a hydro date on them.  This is what the Air Arms Manual recommends : IF COMPRESSED AIR IS BEING USED OTHER THAN FROM A DIVING SHOP, THE INSIDE OF THE CYLINDER SHOULD BE
INSPECTED FOR CORROSION AT LEAST ANNUALLY. IF IN DOUBT CONTACT AIR ARMS FOR ADVICE.
IN ANY EVENT THE CYLINDER SHOULD BE INSPECTED EVERY TWO TO THREE YEARS DEPENDING UPON USAGE. AIR
ARMS CAN PROVIDE THIS SERVICE AT A REASONABLE COST.        kirby