Valve threads
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Posted by: behrouz ® 08/08/2005, 03:24:20 Author Profile Mail author Edit

I have problem with CNG valve threads. In the ISO 15500 standard ,the recommended thread size of the cylinders is: - 2-12 UNJ (nominal 2") and Jointing components shall provide gas tight sealing performance. So my question is: In the standard ,do not mentioned to the fitting of threads.What is your suggestion for the fitting class(2B,3B,...) of valve threads. thank you

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Re: Valve threads
Re: Valve threads -- behrouz	Post Reply	Top of thread	Forum

Posted by: kelly_bramble ® Administrator 08/08/2005, 08:27:56 Author Profile Mail author Edit

I am not familiar with the ISO 15500 standard, however years ago I worked a design on a CNG fuel system for commercial and automotive vehicles. I suspect that you are talking about the threads used on the pressurized storage, or the adapters used to fill the storage tank. I do know that the UNJ thread series is a British originated thread series. The thread series is known for applications requiring high fatigue strength. The way this was accomplished on the thread, is to add a larger than normal root radius at the intersection of the threads (for better stress distribution). Knowing that your application is likely to see high fatigue, and that the thread is usually toleranced this way, I would suggest you either use 3A or 3B thread class designations. The highest tolerance thread designation is the safest route in any case, unless you only intend to use the thread under comparably light pressure, such as below 250 psi.

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