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Re: filling pressure

Posted By: john anderson
Date: Monday, 29 April 2013, at 3:27 p.m.

In Response To: Re: filling pressure (SVP Neon Equipment)


> Over the years there have been several
> similar charts all claiming to be
> "ideal" for various reasons, and

Never claimed the data in this chart was "mine", and certainly not that anyone else's method was inferior. I didn't come up with the research behind it, the European Sign Association did almost 20 years ago.

The main factor affecting the best fill pressure is total tube volume. Volume changes with diameter, but it changes even more with length in the typical neon tube. I'm not sure why the old US charts stuck with only measuring one of the parameters and not the other. I guess they didn't want to make it any more complicated. Same with Neon vs. Argon/Hg. the tubes operate differently and have different characteristics. Again, not my research.

The original ESA chart lists all the lengths in CM. For example if the tube was from X-to-XX CM, fill it to this for the specific gas and diameter.

All I did was categorize the various CM lengths into 4 categories: 1ft, 2ft, 3ft, 4ft. You pick the length that is closest to your particular tube. Sure, you could be more precise if you want to take out the map wheel for each tube. The formula for tube volume is simple. But applying these categories puts you much closer into the range that syncs with total tube volume.

If you are curious how both diameter AND length affect tube volume, I'm attaching a link to a calculator you can scale in mm, ft, yards, etc. If you play around with it using typical neon unit lengths and diameters, you'll find length affects tube volume even more than diameter for most units.

The goal in the chart I made (which again just converts units and summarizes the ESA chart and research)was to make something easier to use for US-based units (feet). Almost any pumper can look at a unit on the table and intuitively estimate whether the total footage is closest to 1ft, 2ft, 3ft, or 4+ ft... then quickly match it up with a fill pressure. With practice, I've even found I automatically extrapolate values for say a 1-1/2ft tube. Either way you are hitting the mark based on total volume better than something only based on diameter.

This was my solution to making it easier to use in my own neon shop. If someone else has a better idea then by all means use that or whatever works best for you.
John


tube volume calculator

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