Hi, how lucky, you have got hold of one of my Baldwins. The most likely sudden loss of pressure in the loco is the smplest and most obvious one. The in flue super heater tube (steam drier) has burnt through. If this has happened it is because some body not understanding gas firing has had the burner out and arranged it so that the burner slots face the steam pipe in the flue. So check this first- hook up an airline ending in an old syringe barrel. Plug and twist this into the boiler water fill socket. Pull out the smokebox door so you can see down the flue and turn on the air and open the regulator. Any air? any Water visible in the flue?. If there is it is the superheater, if not, keep the air on and hold the front end of the loco in a bucket of water . Any air bubbles??? The air has got to be coming out somewhere and that will be the same place that your stea pressure is vanishing from.
The saddle of the loco is as the prototype. The steam pipe and exhaust are soldered into sockets inside it. These were soldered in with Comsol. Misuse of the loco that caused it to get hot enough to melt this would have caused complete deconstruction of the body platework so you can rule that out I think.
Are the valves OK? ie put the loco in midgear, open the regulator with the air line on and see if there is a continuous hiss as you slowly rotate the driving wheels. If the hiss comes and goes slightly the valves are probably ok. DIsconnect the conrod from both sides , air line on, in gear, do the piston snap back and forth when the wheels are rotated by hand? If yes nothing too bad is amiss. If they are sluggish (one side or both) the O ring has gone.
You can report what you find to me on
aboyne.workwright@gmail.com and I can advise you if you report what you find.
Water gauge, these do tend to work after a fashion. If I were building the loco today I wold keep the design but use wider pipes. One thing you can do is overhaul it. You can remove the glass the risk of breakage is very low as long as you realise you only have to move the brass caps apart by 1-2 mm to get the glass tube out. The advice above though is good you can get quite good results by washing the boiler out with some white vinegar. One thing I have just done to one of my Baldwins is replace the centre pin in the water gauge with a stainless steel one. 1/16 nom SS rod threaded 10BA and re-use of the original nuts. Do not overtighten, if you do this it is not so much the risk of breaking the glass but of the O rings compressing and narrowing the water way too much for the gauge to function. I put mine together with water in the boiler and only tight enough to stop drips. I then raise steam and only tighten it enough to stop any leak at 60 psi, then give the nuts (top and bottom) 1/4 turn AT MOST.
The boiler can be removed. Remove pressure gauge , remove safety valve(1/4 drive socket through dome) Un nut the steam pipe from T at the front end, take off cab It has Bayonets plus bolt under floor, take off gas pipe between burner and valve, remove firebox cover. THe boiler is a push fit into the smokebox so you will have to take the bunker off too. All this is a bit of a bore to do, so I would only do it if I had to!
My final comment - If you have the original instructions that came with the loco and its original boiler certificate you might find wording to the effect that "Wrightscale support their products.If you have a problem with one of our products, in the first instance contact us, we will make good the problem provided that the locomotive has not been altered or repairs attempted by others......" Even now most of that applies to your engine I will still support it. I am just rebuilding a 25 year old loco that was dropped- at modest cost to its owner, really just the cost of new etches. All the best with your refurb. Workwright.