Pressure Gauge

[GWR 101]

Hi, I am just about to undertake the pipe bending for the boiler pressure gauge and I was wondering about its height in respect of the boiler. As you will see from the photo below I am intending to connect it to the top of the manifold, I understand that a "U" bend is required what I can't seem to find is any requirement to how far down this should be in respect to the boiler and if there is also any requirement for the gauge to be above the top of the boiler. Any guidance would be greatly appreciated.

 

Many thanks. Paul

[mbrown]

Hi Paul,

The important thing is that the U bend below the gauge should be able to trap some condensate so that the pressure is transmitted to the gauge through a column of water and the gauge is not directly exposed to steam. Obviously, on first steaming, vapour will condense in the tube and the U bend is so that the water will stay there (since it can't escape via the gauge) and not drain back into the boiler. I would go for at least 3/4" between the lowest point of the U bend and the tail of the gauge - but if you've got room for a bit more, I would use it.

The height of the gauge in the cab in relation to the boiler is irrelevant, provided there is the U bend (sometimes known as the syphon) beneath the gauge.

With your connection on top of the manifold, I would take the pipe up as far as the cab roof, then lead it down to at least the level of the top of the boiler, then up again to the pressure gauge which you could mount in whatever location is most visible from the driving position. Find the best location and just make sure the gauge is then above the bottom of the syphon U bend. Exactly how you run the pipe from the connection on the manifold to the gauge is largely a matter of what looks neatest, but if you start from that top connection, the pipe could follow the contour of the cab roof and then head downwards beside the cab side, before turning upward to connect to the gauge.

Hope this helps.

Malcolm

[GWR 101]

Hi Malcolm, many thanks for taking the time to reply in detail. As its a freelance design I am not too constrained regarding the cab shape and size so there is plenty of room (the cab is partly shown in the photo). I will as you suggest follow the cab roof and left side, I have room for at least an inch above the lowest point of the U bend and the bottom of the gauge which still allows it to be visible when driving. So tomorrow I will bend up the pipe and undertake a trial fit, once again many thanks for your help, regards Paul

[smallbrother]

Hi Paul,

Been puzzling me for a while but how do you attach the firedoor frame to the boiler?

Cheers,

Pete.

[jackrae]

Industrial practice was to prefill syphons with water before the gauge was fitted and it wouldn't be a bad idea to do it on your loco. Once the gauge is fitted that water will remain there even if you turn the loco upside down.

[GWR 101]

Hi Pete, as you might be aware I had my boiler made for me. I supplied the boiler maker with the door complete with hinges and latch, he then silver soldered tapped bosses into the boiler to suit. The eagle eyed will probably notice that it is hinged the opposite side to the drawing, he did this because he believed it could be hampered by the water level gauge and associated pipework. I fitted the door and latch using stainless steel bolts, Hagley had kindly provided me with a sample to follow for the shape of the door and baffle. Hope this helps, regards Paul

[GWR 101]

Hi Jackrae, many thanks for your reply, I was wondering about that and it does seem a logical approach, so I will give it a try. Many thanks Paul

[Shawki Shlemon]

When I make my boilers I fit blind bushes in the back head to secure the door hinges / frame .

[mbrown]

If you are right handed, it makes good sense to put the door hinge on the left as you have done. My "Lyn" has the door hinged on the right, as per prototype, but it feels awkward and the door can get in the way of the shovel which tends to come towards the firehole from slightly right of centre because of how I am holding it. (Hope you're not left handed!)

Malcolm

[GWR 101]

Hi Shawki, yes this boiler also has blind bushes, I was very fortunate that the boiler maker was recommended to me and he is well known in the model engineering fraternity. Regards Paul.

[GWR 101]

Hi Malcolm, I must admit I hadn't considered that it might be easier to fire with the door hinged on the left, as I stated I cant' claim that it was my idea, and yes I am right handed. I am presently soldering up all the fittings on the pipework (including the pressure gauge), as the assembly is reaching the final stages I have fears that I will miss something and end up having to take it apart again. I think I need one of Jim's soothing ales.    Regards Paul.