RuneK said:
Today I steamed up the Argyll. It ran smooth!
The pressure gauge did not work, but that is most likely an easy fix.
Good news (apart from the gauge).
I seem to remember being told the following, so it's very probably true.
Loco pressure gauges are relatively delicate, they like to work on air and may be damaged with water or steam.
This is the reason for the U tube between gauge and boiler.
The water is provided by the first charge of steam condensing in the initially cold tube, the air is already in the tube.
The steam pressure compresses the air via the water and the air operates the gauge.
If you find you need to replace the gauge I suggest you ensure that there is air rather than water in at least the part of the U tube nearest the gauge when fitting the new gauge. Also make the joint steam tight.