Certainly, and a lot more.

Its a special Borosilicate glass which is incrdibly strong, although having broke one once when I was steaming up (acciently smacked it with the shovel) it is a good idea to fit a guard around it.

Regards

Lofty

Full boiler pressure is applied to the glass tube. Thick walled glass as intended for gauge glass use, from a model engineering or industrial supplier, will take the pressure. I like the stuff with the blue stripe, it helps to see the level. Never had one burst on its' own. It's also important to have the glass touching only the rubber seals, and not have the metal gland nuts or fittings contacting the glass applying stress to it at a small area. Best to follow a proven design for your gauge glass and fittings arrangement, preferably with shutoff valves above and below the glass, and a blowdown valve for the glass, with a drain below the cab.

Cheap glass tube trinkets from the dollar store or ex neon sign glass tube or any other glass tube not specifically rated for gauge glass use likely will not take the pressure.

As usual, I expect 15 people on the forum will disagree. The above is just my $0.02 worth based on my own experience.

Excellent point Jeff, its also worth noting that the gauge glass nuts are only tightened finger tight.

Regards

Lofty

In the past, I've bought gauge glass with a blue line embedded in it, Schellbach I think Reeves listed it IIRC. However, I found that it wasn't truly round, at least the pieces that I received, which made sealing difficult.

I found that the plain borosilicate tube was better in this respect.

Some folk also reckon that lined tube is also more easily broken.

Just looked, Reeves don't seem to list the lined tube any more, just the plain.

Edited By Clive Brown 1 on 01/02/2018 10:42:28

I looked up some numbers

Ordinary glass has a tensile strength of about 30-40 MPa, but toughened glass is more like 200Mpa

Annealed copper has a tensile strength of about 200 MPa but a yield stress of only about 70 MPa.

So you could argue a toughened glass tube is stronger than the boiler shell… but obviously a bit more fragile!

Neil

It all depends on the gauge location/aspect, loco, track and experience, but all said I have never had any problems. There are usually a lot of things to think about and do 'on the hoof' but you will soon get the hang of things. Probably!

Hi Julian,

You say discard ordinary gauge glass with greenish ends. May I ask why and what does the greenish colour indicate?

John

I don't actually agree with Jeff re separate shut off cocks top and bottom of the gauge as in 3.5"g and 5"g these restrict the passageways, and in any event I have never found them necessary.

Cheers,

Julian (first of Jeff's 1 in 15)

Agree, and there is another reason….

Having had a breakage, and when it happens believe me you don't forget it, it was near-enough impossible to get to the valves.
In retrospect, the time would have been better spent getting rid of the fire!

Good maintenance in this area pays off – I change the glass and seals each season – actually over the top but i feel better.

Dimly remembered from School Chemistry, I believe a greenish tint at the ends is a strong hint that a tube is made of soda glass. This is the stuff that melts in a bunsen flame. It's inexpensive, easily worked, and very handy for making simple glassware in a lab. Whilst brittle, it withstands high pressures provided they are applied slowly. It expands and contracts more than other glasses when heated. Not ideal in a locomotive sight gauge, where the temperature goes up and down and a tap might shatter the glass.

Although soda glass tubing could used at a pinch there are better alternatives.

Dave

Just measured the diameter and thickness of a piece of gauge glass tube. The hoop stress in a 6mm OD 1mm wall tube with 6 bar inside is 0.9 MPa, so I doubt it is strength which renders 'ordinary' glass unsuitable. Having said that I'm sticking to borosilicate, otherwise known as Pyrex. It's not that expensive, not worth risking a nasty scald.

Too true, and when it breaks on a cold day the amount of vapour suddenly ejected means you have no chance of seeing what you are doing, the best I could manage at the time was to shut the blower and the air inlet and push in as much cold water with the tank pump as possible.

Luckily I had only just lit up and there was only about 40 psi on the gauge at the time.

It was a little easier with a full size Sentinel, although the cab was full of a very hot fog in seconds – amazing how quickly you can get out of those little doors – and that was just a seal failure, not a groken glass.

Regards

Lofty