Selpac Bourdon Tube Depth Gauge

[JamesBon92007]

I recently acquired this gauge and don't understand how it is supposed to work. It is a Bourdon tube but there is no outside opening--the plastic case is completely sealed. I also have an old US Divers Bourdon tube gauge but the tube opens to the water which straightens the tube and turns the dial. There are two holes at the bottom on the back of the mechanism so is it possible this is reading air pressure? That's the only thing I can think of. At six feet in my swimming pool the dial does not move.

Thanks.

 

[Luis H]

From what I can see in the pictures, that is an oil filled depth gauge.

The case is flexible enough to transmit the outside pressure on to the oil.

The oil is not compressible, so it transmits the outside pressure to the outside of the Bourdon tube.

When you increase the outside pressure of the Bourdon tube it tends to coil in tighter.

The coiling action moves the needle to show the depth.


Think of this Bourdon tube working in the opposite direction as a pressure gauge.


You should be able to view the movement by lightly squeezing the gauge. Do it only very lightly. The case is designed to get uniform pressure. When you squeeze it it is not as uniform and if the plastic in theory could get damaged if it is overdone.

 

[JamesBon92007]

Thanks Luis! I thought it should (probably) be oil filled but didn't see any evidence of any oil. It must have leaked out a long, long time ago.

Do you suppose I could refill it and seal it? There is a small crack in the case. If so, what kind of oil?