Why did the GWR not use smoke deflectors?

Come to think of it, why didn't the LNER use them on all their express locomotives? Was it a question of aesthetics?

Maybe I'm over-simplifying the situation here - but so many of the Southern locos had them, as did LMS. Surely they were a benefit to crews, in which case, why were they not employed more often?

 

they didn't need them..... simple as

 

Why did the Southern locos need them?

 

Problems with exhaust from the chimney obscuring the drivers view on the King Arthurs. Maunsell did some research, including trials of a number of designs and concluded smoke deflectors improved things. As a result all his designs (N15, LN, V, U & N) got them retrofitted or fitted from new.

Presumably the GWR's drafting arrangements didn't cause problems so smoke deflectors were never felt necessary.

 

By the time they came into use generally, the G.W.R. had retreated into "not invented here". An example of this away from the locomotive field can be found in the antiquated doorlocks fitted to post W.W.II coaching stock.

PH

 

It will be interesting to see if 6023 runs into any issues with her radically revised draughting that's being worked up.
There could be a dilemma there: she was back revved to single chimney so as to experience again a single chimney King, but if the revised draughting caused by the loading gauge change means she no longer sounds like a single chimney King, (or worse still smoke is a major problem making a need for s**** d********s) would it be better to return to a double chimney?

 

Also GWR engines had a significant taper on the top surface of the boiler, coupled with tall chimneys (due to the more generous loading gauge), and higher exhaust velocity, all of which meant that steam was carried well clear of the cab.

 

Sorry but that's total nonsense and I can quote 18000 reasons why...or even 18100

 

The clue is in the title, Smoke deflectors, not Steam, not Exhaust, Smoke, and what is one of the characteristics of Welsh steam coal? its Smokeless ! Deflectors not required.

 

So why does one heritage railway which uses such stock find it necessary to print leaflets to be given to everyone buying tickets which warn them about the locks?

PH

 

I'm not a big LMS expert, but my feeling is that most later LMS locos (i.e. the Staniers) didn't use them. Jubilees, Black 5s, Stanier Moguls, Princess Elizabeths (whatever they are called) didn't have smoke deflectors; only the Duchesses at which point you are getting to very big boilers and therefore very short chimneys. Amongst LMS locos, isn't it more the older designs that have them, i.e. Patriots etc? Presumably the combination of draughting and boiler shape are very different on those locos than on the later Stanier designs.

There are good reasons for not using smoke deflectors if possible, notably better forward vision, not to mention extra expense. So presumably designers fitted them as a last resort, i.e. when the combination of boiler size, chimney height and exhaust velocity made them essential to provide forward visibility. Presumably those combination of factors meant that drifting steam was never a problem on GWR locos.

Tom

 

But what about the later rebuilds Tom, Scots, Patriots & Jubilees, all had them fitted ? and most probably THE most attractive of all smoke deflectors, along with the A3 Gerry Blinks !

 

Calling them smoke deflectors is a misnomer. They were there to deflect the exhaust no matter what it consisted of.

 

I've seen more than one source suggest that a boiler tapered at the top plus the shoulders of the belpaire firebox creates useful airflow for clearing the visibility. Presumably the velocity of the exhaust is a factor too.

 

Interesting to note that the official title for the deflectors fitted to the Brits, Clans and 9Fs is Plates for Preventing Down Draught.

 

Maybe because its their way of complying with the ROGS legislation. Please remember that the legislative environment we operate in is vastly stricter than what prevailed in previous decades. If someone fell out of a door that was not properly secured, the first reaction from the investigators would be "How does your SMS (which ALL railways need to have) mitigate the risk of this occurring?" - It is unacceptable in the eyes of the regulators to simply blame the user these days. Putting information about door locks and other safety information (i.e. steam engines have hot surfaces and emit smoke and smuts which could get in peoples eyes) in a leaflet issued to every passenger group is one way of mitigating the risk - and having lots of platform staff to monitor the train before and during departure is another.

I would also add that with the demise of slam doors on lots of trains on the national network, even opening a bog standard Mk1 door can be hard for some - there are even tales of people pressing the rubber bump stop thinking it is a push button and the door will open automatically for them.

 

The need or otherwise for smoke deflectors has one or more of several causes. Initially, a steam locomotive is aerodynamically a poor piece of kit, having a fairly large, flat surface - the smokebox ring and door - being pushed into the air ahead of it. This air is forcibly moved out of the way, both to each side and upwards, and this movement away causes a low pressure areas above and either side of the boiler barrel, into which the exhaust is drawn downwards, so interfering with forward vision. Smoke deflectors extend forward of the smokebox door and back along the smokebox, and the effect is to catch and channel the air that would otherwise be forced out rearwards along the side of the boiler, so creating high pressure in this area and forcing the exhaust upwards, clear of the driver's vision.

So what factors cause this drawing down into this low pressure area? Firstly, the sheer size of the smokebox being forced forward: the bigger it is, the more air it will displace, the lower the air pressure along the boiler sides. Secondly, the height of the chimney: the higher the chimney, the further the exhaust is from the low pressure area on release to atmosphere so the less likely it is to be drawn into it. Thirdly, the pressure of the exhaust from the blastpipe: designers try to reduce this as much as possible as it is effectively acting on the wrong side of the pistons, so reducing the engine's efficiency. But the lower pressure fails to lift the exhaust high enough, so is again drawn down into the low pressure area.

Staying with the LMS, smoke defflectors were fitted only to engines with large smokeboxes and/or double chimneys, where exhaust pressure wais low. The standard Jubilees had a fairly small smokebox and tall chimney but the rebuilds had bigger smokeboxes and double chimneys, so needed deflectors. The Lizzies didn't need them: single, and tall, chimney. The original Coronations didn't need them either, not until fitted with double chimneys.

Now apply that to the GWR: relatively small smokeboxes due to the taper boilers, no double chimneys, taller than average chimneys, and, as the noise will show, a lot of pressure in the exhaust to lift it clear. So they weren't needed.