Peppercorn A2 "Smokebox Fittings"

[majormagna]

This is where I show my inexcusable lack of knowledge...

Some A2s have A3 style Superheater Header covers, whereas others have ones with an almost triangular cross-section (60532 as an example)... I assumed it was something to do with the double-blastpipe, but recently I saw a photograph of 60539, with double blastpipe and the former fittings, as well as the lack of "box" behind the chimney, which Blue Peter sports, just the small rounded fitting, (speaking of which what is it for and what is it called anyhow? I assume something to do with the superheater arrangement...)

I was just wondering what the functional differences are, whether all A2s got the same style of fittings as Blue Peter, and if not, why not?

[Solario]

Hi Majormagna,

The "box" behind the chimney on Blue Peter & a few of the other Peppercorn A2s housed the multiple valve regulator.

I think that the "small rounded fitting" which you refer to is the anti-vacuum valve, often referred to as the snifting valve. This valve opened when the regulator was closed allowing air to pass into the main steam pipe to prevent smoke and ash being drawn into the cylinders. I think that the air also passed through the superheater elements to stop them burning, I'm sure that someone will be able to confirm this. You will see this fitting on many ex-LNER locos.

I'm not sure what anti vacuum device other railway companies provided, I would be interested to know.

Solario

[Hatfield Shed]

Locomotives of Crewed design have a pipe often under the vacuum brake ejector pipe running back to some gubbins (often as far back as on the firebox side) with a vertical pipe descending from it; Riddles followed this pattern on the BR standards. Maunsell locos often have them on the smokebox sides behind the chimney, presumably directly mounted on the ends of the superheater saturated header. Not a clue on Pighill's products, since they basically hardly bothered to superheat at all. Maybe that little teardrop fitting on the rear edge of the smokebox?

Where did Bulleid put them? Probably on the front bufferbeam or the tender, just to be different...

[ten ten]

As engines vary greatly -even within companies,difficult to be specific what pipes do ,the pipe under the vac ejector pipe may be steam supply to the blower or the steam supply to ejector if that is mounted on smokebox side. Small bore vertical pipes may well be drains from drip valves. As to Swindon products,the superheat oil piping to regulator/valves is fed from the cab hydrostatic lubricator to the smokebox under the boiler cladding to emerge near the tear drop mentioned,which contains shut off cocks to the supply pipes within the smokebox.The GW vac relief/"snifter valves are on the steam chest casting behind the steam pipes where they pass through the footplate, on Bulleid rebuilds they are on the external steam pipes,about level with the footplate Probably in the same position, but hidden by the cladding on the original Spamcan design.

[majormagna]

The "box" behind the chimney on Blue Peter & a few of the other Peppercorn A2s housed the multiple valve regulator.

I think that the "small rounded fitting" which you refer to is the anti-vacuum valve, often referred to as the snifting valve. This valve opened when the regulator was closed allowing air to pass into the main steam pipe to prevent smoke and ash being drawn into the cylinders. I think that the air also passed through the superheater elements to stop them burning, I'm sure that someone will be able to confirm this. You will see this fitting on many ex-LNER locos.

Ah thank you, yes I remember it being called a snifting valve now, I assume the multiple valve regulator cover also houses the snifting valve? I've also noticed that the only locomotives I've seen that have them are superheated, but it may just be a coincidence.

So not all A2s had multiple valve regulators?

Again, does anyone have information on the differently shaped superheater header covers, some A2s had rather flatter versions of the style used on A3s and V2s, but Blue Peter and others (it seems to be limited to those with the multiple valve regulator housing) have differently shaped ones, almost like they've been turned 90 degrees.

[Solario]

I think that there were some British locos fitted with Trofimoff (piston) valves which did away with the need for snifting valves.

I'm sure that the LNER tried them on one or two locos but I can't remember the details.

Can anyone shed any light on this?

[Blink Bonny]

Ay up!

Couple of things, here.

Most Stanier locos had their snifting valves mounted beneath the runing plate by the cylinder. There was also the Fowler-Anderson design of bypass valve, mounted on the cylinder draincock, which basically did the same thing but was a classis use of a sledgehammer to crack a nut. They were cumbersome and complex and the reason why the early LMS streamliners had that little "flare" to the bottom of the casing around the cylinders. On 4Fs the snifters are at the base of the smokebox, on the 4-4-0s and earlier 0-6-0s, down between the frames just to make life harder for the fitters....

Bullieds originally had them discreetly hidden inside the casing but the rebuilds had them behind the deflector.

Not many A2s had the multi-valve regulator. It was an expensive piece of gear, bought in from an outside contractor whereas the standard grid type regulator in the dome could be made in-house and was cheap. It must have been a success otherwise Riddles would not have sanctioned its use on the Pacifics. I'm always bemused as to why the 9Fs got the grid type regulator. Maybe economics were biting by then?

[Postman Prat]

Am I correct in saying that the multiple valve regulators were only fitted to the locos rebuilt with a double chimney?? 60539 was built with a double chimney (the only one of the class) and therefore had the standard fittings.

[majormagna]

Am I correct in saying that the multiple valve regulators were only fitted to the locos rebuilt with a double chimney??

It's possible that all the A2s with the MVR had double chimneys, but Ive seen photos of A2s with double chimney, yet without multiple valve regulator housing, so the two were not mutually inclusive.

Neither does it appear to be mutually inclusive regarding double chimneys/multiple valve regulators and the "oddly" shaped superheater header covers, seen on Blue Peter and some other A2s... Still no ideas on that one?

[Coronach]

As far as I'm aware, it was only 60538 and 60539 that had double chimneys without multi-valve regulators. I think it was only 60529/32/3 which had this equipment. It makes me wonder if this was an evaluation exercise for the equipment that would appear on standard pacifics shortly after rebuild. Britannias seem to have a not dissimilar arrangement.

Dave.