Thank you Achim, Roger, and Ian!
I might be wrong but if the bourdon tube expands, ie opens out, under pressure, won't that move the pointer to the left? Or have I missed something?
Interesting question, Ian!
The end of the bourdon tube moves upward and to the right, under pressure. And as it moves up and to the right, it pulls the link which is connected above the pivot point of the needle. And the needle moves to the right.
Here you can see that the link connection on the needle is above the pivot point:
And here's a close-up of the link connecting the end of the bourdon tube to the needle.
When pressure is added inside the bourdon tube, it increases the diameter of its curve. Since the left end is solidly attached to the stem, it doesn't move. But that increase in diameter makes the other end (the end on the right of the stem) move outward and upward just a little bit. The entire movement isn't much over 1/8". But it's enough to move the needle quite a bit. I don't know what the full scale is yet as I haven't tried it with the gauge fully assembled. That may come later today. We'll see
Here's a video of the bourdon tube expanding under pressure. Hopefully, you can see what I mean about moving up and to the right a little?
This has been a very rewarding little project, that's for sure!
Kim
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