Finescale - of a sort?!

[simond]

I can see merits in both suggestions, though I’m at a loss to understand why not-very-hot steam should be any more deleterious to the bourdon tube than very-hot water.

I wonder if ensuring that the tube was full of water made it a bit heavier, thus reduced any tendency to vibrate? It would still vibrate, I guess, just more slowly, which might be preferable.

however I found this, which reiterates the point about temperature

Why Do I Need a Steam Siphon and How Does It Work?

A steam siphon can be a very useful device. If you’re wondering how it works, this article will teach you.

blog.ashcroft.com

 

[Peter Insole]

That's a relief Simon, I was rather afraid that I might have been talking nonsense - as well as being frustrated by not being able to immediately lay my hands on any historic "proof"!

Pete.

 

[Giles]

Entirely right! The water in the loop acts as a 'buffer' protecting the gauge from the temperature and latent heat of the live steam!
One sometimes gets hammering from the injectors, but I've never notice it affecting the pressure gauge over-much.

 

[Peter Insole]

I do hope you are not embarrassed by all this Dog Star... but I fear you are not the only one that has, nor will be misled by some "old boys", who we would all much prefer to show respect, telling tall tales!!

Pete.

 

[mickoo]

I'm afraid to say Dogstar is also correct, it is for reducing the risk of fracturing at the gland, generally caused by expansion and contraction but more often through vibration; as a secondary bonus it leaves spare pipe to remake the joint if it did crack.

Often the runs are long, so rather than having to remove a whole section for a fracture ½" from the gland you could simply shorten the loop, swage the end and re-terminate very quickly. I never worked on steam, just industrial gas water boilers so we never had steam or condensation to worry about, just very hot pressurized water.

A similar principle is (should be) applied to wiring electrical panels, well that was what I was always taught, you always ran the cables the long way around the cubicle before terminating in the fuse/breaker. Most panel failures are due to heat at the fuse/breaker and subsequent cable failure, having slack in the panel allowed for a quick chop back and repair, saved my butt on many occasions. Same for any sensors at remote locations, always leave a loop or two of cable before it enters the device.