Water Gauges

Cutting: This is the correct way to cut a glass tube to correct length:

First, file a small notch (just a scratch will do) at the point where you want to cut the tube;

Then holding your forefingers on the tube at the points indicated on the drawing, gently apply pressure opposite the notch with both thumbs; the glass will snap very cleanly. Bare hands are fine, but the use of thin leather gloves may be a wise safety precaution, as well as protective eye glasses or goggles.

Annealing: After the tube is cut, there's still one very important thing to do: anneal the ends! This removes any sharp edges, and stress relieves the glass which may otherwise lead to a fracture during use at a later date. It also slightly rounds the ends, which prevents damage to seals such as O-rings while inserting the tube into the gauge assembly.

Hold the newly cut end in a gas flame [a propane flame, or the common gas stove flame is OK], slowly inserting and then rotating the glass while it is in the flame, so that the glass heats gradually and evenly. Keep it there until the flame turns bright orange at the tube's end, and the glass edge melts ever so slightly, giving a nice, smooth, rounded edge. A few tries will get it perfect.

Click here for photos of cutting and annealing.

Sometimes, it can be difficult to see the water level in the glass, or be able to tell if it is completely full, or completely empty (a potentially boiler damaging condition!), and a visual aid is used to assist in determining the water level. This can be a coloured line (usually blue or red) painted along the glass during manufacture, like in a thermometer where the line appears thicker, or something more elaborate.

Here is a little visual example of how to make the water level more visible in the glass, or tell the difference between full and empty.

Place a diagonally striped background, 1 to 2 tube diameters behind the glass, and you'll be able to see the water level much more clearly than without this aid!

These are actual, un-retouched photos of a 6mm (1/4") dia glass tube half filled with water, shot against a diagonal pattern. The water level shows still more clearly. For installing in the cab, make the pattern just about as wide at the tube, there will not be a distracting background (as here, for demonstration only).

• The lowest visible part of the tube (the so-called "bottom nut") MUST be more than 10mm above the crown sheet or flue tops within the boiler
• One water gauge is the minimum compulsory requirement, but often, if cab or back head space permits, 2 are installed.
• The top connection may be via a tube to the boiler if space is small, it only carries steam with very little flow. However, it should have its own dedicated boiler fitting and not use a spare outlet on the turret, otherwise a false reading will be obtained due to pressure change when other accessories are used.
• It is desirable to have a gauge blow down valve at the bottom of the assembly. Occasionally bubbles form inside the glass tube preventing an accurate level reading, and can be cleared using this valve.
• Use a piece of steel rod, the same diameter as the glass, during assembly to adjust the alignment etc of the fittings. When satisfied, remove the dummy metal rod and carefully insert the real glass as the final step.