Float indicator in water gauge glass

With unerring hindsight, I realise that I should have extended the water gauge on a vertical boiler by about an inch or so, so that it gives me a more accurate indication of how much water is covering the lower tubeplate. I was wondering whether I could perhaps remedy the situation by inserting a "float" in the gauge glass ? Has anyone else tried this? As the boiler is to go in a r/c boat I need to assess water level at a distance.

I have fitted electronic water level indicators in locos and might be able to somehow wangle a sensor through a spare bush but this would still not be easy as it would have to be about 2 inches long.

Mick

Coiuld you just use a taller tube with an 'S' shaped upper connection?

Mick,

Try fitting a strip of material behind the glass which has closely spaced angled marks on it, like a pattern of chevrons. The contrast needs to be good, yellow on black is satisfactory for viewing at a distance.

The presence of water in the tube in front of it will refract the view of the chevrons to make them look horizontal and it is easy to distinguish the level from this change in view.

It is an old trick used on gauge glasses with ship's steam raising plant so that they can be rapidly assessed visually.

Regards Brian

You can get glass with a red line down the back. If there is water in the whole glass appears red.

Duncan,

Could Mick do the same thing by painting a red line down the back? I can't imagine it is much more sophisticated than that.

Regards Brian

I think we have gone off on a tangent...

I think Mick's issue is that the sight glass does on go LOW enough so there is still some water in the boiler when the glass is empty. This is of course the safe situation. If I'm correct then yes adding a float that sits on top of the water will give you some extra range equal to the height of the float above water. Some vintage aircraft used this technique, even going so far as to have the float completely out of sight with just an attached index wire showing in the tube. This also works for an overhead tank with the tube full of fuel and the wire sticking out the bottom of the tank and the float on fuel surface above.

The problem is that you have introduced a significant failure mode. If the float sticks you will run the boiler dry. Probably best to just put up with the reduced running time.

Robert G8RPI.

Thanks Gents. I obviously did not make the situation very clear. Robert Atkinson has guessed me correctly. The gauge glass that I am using is the red stripe type. The problem is that when the tube is "empty" there is still about 1.5" of water in the bottom of the boiler. The boiler is only 3" diameter and just over 6" in height so this is a significant amount. Poor planning is to blame. I take Robert's point about the float sticking and I am beginning to dislike the idea. I will try and move forward on the electronic water level.

Mick

I don't know if you plan to get the boiler 'certified' Mick - but the Orange Book guidance in this area is fairly simple...

" 6.7 Water level gauges shall be so constructed, mounted, or adapted such that the lowest water level visible in the gauge glass indicates that the level of water is above the firebox crown sheet. "

So if I understand your problem correctly then your current gauge (although not ideal from your point view) does seem to meet the essential point of this criteria (albeit it's a vertical boiler). Speaking personally, I would be more concerned about using a 'float' because of the possibility of it sticking. However, this is one of those issues that is somewhat subject to inspectors 'discretion'.

So if you need (for Insurance or Club reasons) to have the boiler checked, then (as always) it's best to ask your Boiler Inspector for his views.

Regards,

IanT

Thanks Ian. Yes, it does err on the side of safety as it is. I have been talked out of the float idea. I will proceed with an electronic LED indicator as I think that I have worked out a solution using a spare bush.

Mick

On full sized boilers, not only must the glass be above the firebox, or tubes, level, but the gauge glass's bottom fitting onto the boiler shell must also be above the firebox or tubes.

This builds in an extra safety margin. If you see no water in the glass, blow down the glass and find water will rise up from the bottom if the top cock is closed, you know you still have water over the firebox/tubes and it is safe to add more water. But if none comes up the glass when top cock is closed, don't add water as it could fracture an exposed firebox or tube. Shut down boiler immediately. The next steps you take should be boiler room steps - two at a time.

I imagine model boilers would be well served by the same principle.

Having decided to go for the electronic water level indicator, I have knocked up a sensor which will feed into a spare boiler bush and go about 1 inch lower than the bottom of the gauge glass. When the circuitry is complete an LED will tell me when I have about 1/2" of water covering the tube plate. I had worried about producing an insulator with a copper core which I could bend into a right angle but I solved that problem by using shrink tubing. I now have an early warning from the sight glass and a shut-down warning from the LED. Thanks for the interest.

Mick