The LNER Encyclopedia

Hi all,

After a quick look through some of my books for some information I noticed that Flying Scotsman has had two variations of her dome. The round one which she was originally fitted with and a banjo dome which was fitted at a later date. Can anyone answer a few questions for me please;

Where these domes standard to all A3's?
When was Flying Scotsman Fitted with her banjo dome?
What advantages does the banjo dome have over the round one?

Regards

Karl

Karl,

The steam collected from the top of the boiler space must be dry. When a loco is working hard most of the steam will be evolved close to the point where it is collected as the pressure will be lowest at this point.
There is a danger that the steam evolving from just below the surface of the boiling water will carry liquid water with it that will then be carried into the cylinders and could cause priming, so damaging the cylinders, possibly catastrophically.

Small boilered locos could have a tall dome and dry steam could be collected from near the top of this protuberance, well away from the water level. Ivatt chose to collect the steam in his domeless boilers using a long horizontal perforated pipe. Poor water quality affected the tendancy to prime.

As boilers got larger the height of the domes diminished to keep within the loading gauge and alternative designs were tried.

As originally built with boilers rated at 180 psi, the A1s all had round domes. When uprated to A3s, the A1s received 220 psi boilers. Some, but not all, were fitted with Banjo domes

I quote Brian Haresnape "Gresley Locomotives":
"The distinctive banjo shaped dome cover housed a slotted steam collector, instead of the usual dome arrangement, in which the steam passed through a series of transverse slots in the top of the boiler barrel before reaching the regulator valve.. This was to prevent priming, as any excess moisture was held by the slots, and allowed to fall back into the boiler barrel."

The first design of Banjo Dome was slimmer at the back than the more prevalent type that we saw in the later years.

Boilers were swapped at general overhauls and so each loco had several different boilers during its lifetime. In BR days a modified A4 boiler was introduced as well.

Yeadon gives the history of the boiler exchanges and leaves it to us to determine what sort of dome was fitted.

1471, later 4472, had the following boilers:
As built 7693
7878 (new) 5/4/28
7804 (ex 2581 27/4/33
7772 (ex 4471) 18/5/35
7785(ex 2561) 3/11/39
Rebuilt from A10 to A3 4/1/47
8078 (ex 2576)
9119 (ex 2505) 15/3/48 ( I believe that this was the narrow banjo type- 2500, 2504 and 2506 were fitted with one from new)
9448 (ex 2747) 16/12/49
27015 (ex 60047) 14/3/52
27074 (ex 60082) 6/4/54
27007 (ex 60077) 8/10/55
27011 (ex 60064) 13/7/57
27044 (ex 60097) 24/1/59
27047 (ex 60100) 9/8/60
27058 (ex 60037) 2/6/62

So it is all very confusing. You need a dated photo to determine which sort of boiler was fitted,

Colombo