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I had an oil pressure gauge out of my tiger moth I was restoring, that wasn't working. It was written in the log book as U/S, so I went looking and found one from Ireland. Once it was in the plane and finally had the engine running, it was reading low compared to the other one. Now I had two bad gauges.
With nothing to lose I took them apart thinking a blockage perhaps. At the pick-up end the nipple screws off, and the capillary will pull out. Looks like it might be soldered in. I used air pressure and cleaner to blow through it, so no blockage there.
Applying pressure from there to the gauge showed no movement of the needle. There is a small tube, the one in the picture has a few curls in it, but the tiger moth one didn't. It is the end of the capillary and is pinched off and soldered.
I used a soldering iron and melted the solder on the end of that capillary and added some air pressure at the other end simultaneously, and the needle then started moving with the different pressures. I then re-soldered the end to form a little drop, and put everything back together. I retested and the gauge seems to work fine. Why this fixed it, I don't really know. But it worked for both my gauges.
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