Gauge Glasses

Forgive my ignorance gents, but I was pondering about these implements. Am I right in thinking that the pressure in the glass tube is equal to that in the boiler itself? This surprises me knowing how brittle glass is and how prone it is to shattering especially if exposed to unequal temperatures.
The gauge glass itself looks like particularly vulnerable with the ability to spray high temperature steam at least temporarily anyway. Had anybody ever known one to shatter? I have heard it was not uncommon in BR days.

 

You are quite correct, the glass is subject to full boiler pressure but it does have a relatively small surface area over which that pressure is acting. Gauge glasses due occasionally break but the protector is designed, not only to resist an accidental knock, but also contain any bits of flying glass while the fireman closes the shut off cocks. Some locos are fitted with a sort of 'automatic' check to reduce the amount of steam/water flying about but can't always be relied on (IMHO). A glass breaking is not as frightening as it looks and 'in the old days' it wasn't unknown for a driver to remove the protector when the fireman wasn't looking and give the glass a 'whack' just so the fireman got the experience of shutting it off and replacing it. It may surprise some people to know that gauge glass does 'thin' over time which is why they used to be replaced on a regular basis. Hope this answers your question. Ray.

 

Indeed it does Ray. Many thanks for your interesting response!

 

Have a look at the link below.

http://en.wikipedia.org/wiki/Sight_glass

 

I've had three break in my lifetime on locomotives. They can go with an explosive bang or merely a gentle pop. The last one happened as I was swapping with another driver and he was on the footplate and I had one foot on the platform when it happened so it was his problem! One of those that went on me shattered the gauge glass protector, which was about 3/8" thick glass. They do have the potential to be lethal. If one goes, you change it asap as you need two working gauge glasses for safe operation. Unless its a GW loco, that is!!

 

With a working pressure of 275 psi I bet it it was a bit of a 'botty twitcher'! It's a long time since I've driven a Sentinel but I recollect that they only had a single gauge glass - is that correct? I had a Marshall roller for many years and that had a reflex glass - not as easy to see in poor light but a lot more resistant to 'shovel rash'. Cheers, Ray.

 

I've not had a loco boiler gauge glass fail in the 36 years I've been on the footplate but I found a gauge glass failure on a 950 psi marine boiler in the 1970s quite exciting!

 

In the last 29 years its happened three times to me. Twice in one day (both with a bang) and once since. The last one was quite funny really as the trainee fireman had just asked about the procedure for changing gauge glasses. two minutes later he was able to try it for himself!

 

Good practice is to change the gauge glasses at every washout exam. The rubbers go hard with use anyway.

 

I know MHR standard practice is new glass at every washout. This could be one reason why a broken glass is a very rare occurrence; always better to try and minimise the risk of it occurring.

 

I'd be surprised if any respectable railway didn't change gauge glasses at washouts or some sensible maintenance period. When you've seen what can happen to them, you'll know why.

 

Exactly as the end of the day any railway which doesn't have a regular programme for changing the glasses would be seen as negligent in the event of an incident from one breaking.

Something that I was taught is that on an engine with two glasses is if one breaks then the other should also be changed asap but when it is safe to do so; as it is probably close to going.

One thing I wasn't aware of is how important the set up of the boiler back head fittings is, if they are slightly out of line then this will be a cause of regular gauge glass breakages.

 

??? Do you mean Klinger reflex glasses? (as mentioned by Marshall5)

 

The problem with Klingers (particularly on wagons) is that you lose a lot of glass length. On our Garrett wagon (with a generally similar boiler size to a Sentinel), the water can very quickly go from the bottom nut to the top nut of the glass, because there's so little volume. A Klinger glass would make it all much more nerve wracking!