Connecting to NGT thread on Steel Cylinder 1

[pacesetter]

Hi, I am considering using a standard DOT-E10869-4500 Gas cylinder as an auxiliary gas bottle for an hydraulic accumulator system. The ports for the gas cylinders seem to all be 3/4-14 NGT as a standard. I don't want to restrict the flow by placing a valve on the end of the cylinder. I want to run 1 inch tube from the accumulator, with a swagelok fitting to SAE, NPT or similar and then into the cylinder. Does a gas fitting exist for connecting to the 3/4-14 NGT?

Thanks

 

[iainuts]

Hi pacesetter,
NGT and NPT are essentially the same. Here's a web page that goes over the differences, but in the end, the differences are not such that you can't interchange them. So to answer the question, "Does a gas fitting exist ..." the answer is yes, just purchase an NPT to tube fitting. It'll fit just fine.

http://www.ring-plug-thread-gages.com/ti-NGT-National-Gas-Taper.htm

One thing you should consider however. Those cylinders are regulated by DOT rules which require some kind of periodic inspection, typically a 5 year pressure test. They are not intended for 'stationary' service, they are intended for transportation where the number of cycles put on them might be a few cycles per week at most. Generally, states have laws requiring ASME vessels for stationary service, though the laws aren't always strictly enforced. So putting a DOT cylinder into stationary service may (strictly speaking) be a legal infraction in your state. The fear is that because DOT cylinders are not intended for high cycle applications, the cylinder could be cycled too many times and fatigued. Also, by having the retest after so many years, DOT regulations try to minimize this risk. The cylinders are cheaper partly because they are made of high strength steel and don't have the same safety factors imposed on them the ASME code has, so they are thinner and under higher stress. This is all done primarily because they are transportable and the need for weight savings (ie: so you don't ship steel).

 

[pacesetter]

Thank you Iainuts,
Your comments has helped me in my research. While the equipment can be easily transported, the operation occurs when when it has been installed on a ship. We do not intend to transport the gas bottles charged. As such, DOT has no authority to enforce it's regulations. The requirements for certification are really driven by the saftey laws which we are trying to meet.

 

[zuccus]

Pacesetter,

While DOT may not have jursidiction, you might want to check into coast guard regulations. However if they are not charged while on the water, then I don't know what they fall under.

Also,
Somebody correct me if I am wrong, I thought all NGT threads were left-handed as opposed to right handed. Or maybe it is vice versa, therefore they won't fit up.

Zuccus