Doc, that tube is nothing but a clear plastic tube that is blocked at one end and open at the other. Unless it is clogged up, there is nothing not to work. If you look closely at the small black plastic piece it plugs the tube on the "deep" side and has slots cut in it on the "shallow" side. The small black square at the bottom of the gauge just under the "feet" is the calibration point. You will notice the plug is directly below that mark. To calibrate it, you remove the tube and shift it to one side or the other until the reading are correct. As water pressure increases, water enters the open side of the tube compressing the air inside. As it does, the water flow into the tube and highlights the yellow (or some other bright color) so you can see the water better. As the pressure decreases, the air pressure in the tube pushes the water back out. These gauges are very accurate in shallow water once calibrated and since they have no moving parts are very reliable. To replace the tube you gently pry the tube from the ring, pretty much the same way you remove an oring. I use an Oring pick. So far I have had no luck removing the black plug in at least a dozen of them (the split side will come out but the solid side has been stuck solid. I don't even try now, I just plug the end of a piece of new tubing with Aquaseal and reinsert it with the 2 ends touching each other, you do not want much space because it will allow air bubbles to form there which will be moved up the tube. The bubble does not hurt anything but makes it a little more difficult to read. Most of them are pretty bad discolored so replacing the tubing makes them a lot easier to read. You can try cleaning the tube before replacing it. Just remove it, pull it loose from the black plastic plug on the split side and run a wire up in it to clean it.
Normally I would offer to send you a piece but I have about sent out all I had....and I started with 25 ft of it -minimum order.. Next time I have a McMaster order I will get some more and keep you in mind.
As for a DH, if you intend to restore and dive it, get either a US Divers or a Voit. All the parts you need to restore them are easily available. The others like Dacor and Healthways are difficult to find parts for at this time. That may change but for now UDS or Voit are the ones to restore.
I hadn't considered these as seavue gauges. I heard about them, but it didn't cross my mind that this was probably one of them. Is it possible that this is a later model, as the SPG portion contains metric readings as well?
