Can anyone explain the gauge glass erosion I am experiencing?I have a 3/4 inch scale engine with a gauge glass about 3/16 inch diameter. It is held by union nuts and sealed by teflon sleeves I made. The original design called for common packing. The glass is eroding under the seals, more so at the water end. The glass was new five years ago. The rest of the glass is clean. The erosion is of course making the seal leak.The boiler is copper. The water is rain water from a cistern and sometimes city water from the Kentucky River. The water is not treated.

If the Teflon is breaking down to HF, then hydrofluoric acid could form and eat the glass. This would happen at temperatures above 400C, 752 degrees Fahrenheit. I don't see how your site glass could get that hot.Here's the material safety data sheet for Teflon:http://msds.dupont.com/msds/pdfs/EN/PEN_09004a3580120c45.pdf

While a bit out the scope of this board,have you checked the pH of your boiler water? Boiler water that is leaning towards the acid side will eat up glasses as you indicated, You want boiler water that is around 10.5 pH,or leaning towrds the base side to help with preventing eating out glasses and metal parts.

I would also join and post this question on the following board.www.smokstak.com then go to the steam engine/traction forum. sounds like you need to use the standard waterglass rubber rings with the brass keeper. These can be bought at a good boiler supply house.

Keep your water pH up around 10.5 and replace the glass. One glass every 5 years should not be considered too many.

Water is a solvent - it dissolves glass, albeit very slowly. We usually change the reflex glasses in our locomotives twice a year. Same with our stationary boilers with tubular glasses- we replace the glass 2 or 3 times a year, whenever it starts leaking. On a locomotive you should pull the valve spindles and rod them out anyway when you do a boiler wash. This is all considered routine maintenance.And in a copper boiler you don't want the Ph over 10. Same goes for a steel boiler with copper tubes. In a steel boiler with steel tubes you try to maintain the Ph between 10 and 11.

Thanks, that was the information I needed. I have found time to operate quite a lot more often in the last few years, and that is probably why I am surprised by the erosion.