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Author Topic: Smoke deflectors  (Read 2621 times)

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Offline petercharlesfagg

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Smoke deflectors
« on: October 11, 2014, 09:01:21 am »
Friends,

Can someone explain why smoke deflectors were needed on some locomotives but not all?

I have seen images of the same class of loco both with and without the deflectors!

Regards, Peter.
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Offline Malc

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Re: Smoke deflectors
« Reply #1 on: October 11, 2014, 10:07:04 am »
Smoke deflectors or "blinkers" work by forcing clean air past the locomotive sides and forcing that air to push the smoke down out of the way. They don't work at low speeds so may not have been fitted when an engine was used for trains other than expresses.
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Offline Jerry Howlett

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Re: Smoke deflectors
« Reply #2 on: October 11, 2014, 10:11:33 am »
First of all I was going to be flippant but then I thought.  VERY GOOD QUESTION Peter.

I know they tried them on the A3 's with the "German type" but that was a late 50's thing.
Can't recall seeing pictures of any GWR locos having them.
SR had them on loads of classes however.
BR days I think just the 9Fs curious eh ?

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Offline Hunslet 707

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Re: Smoke deflectors
« Reply #3 on: October 11, 2014, 10:38:25 am »
Its to do with different blastpipe and chimney combinations. Some having a softer blast and not clearing the smoke from the drivers line of sight. When the A3s were fitted with double chinneys they needed smoke deflectors.

Offline Greybeema

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Re: Smoke deflectors
« Reply #4 on: October 11, 2014, 10:38:46 am »
Smoke deflectors or "blinkers" work by forcing clean air past the locomotive sides and forcing that air to push the smoke down out of the way. They don't work at low speeds so may not have been fitted when an engine was used for trains other than expresses.

Were the smoke deflectors angled in towards the boiler at the cab end of the smoke deflector?  That would cause the air to compress and accelerate thus clearing smoke.  A lot of them seem to be no more than a flat metal plate which, I would have thought, would have little effect.  Or am I missing something?

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Offline Dorsetmike

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Re: Smoke deflectors
« Reply #5 on: October 11, 2014, 11:10:20 am »
The effect of smoke deflectors was to force an updraught to keep smoke clear of the footplate crew's view ahead.

The SR under Maunsell did a lot of experimentation in the 1920s with various shapes and positions before settling on the type seen on  most of their express and mixed traffic locos. Bulleid did further investigation with the spam cans.

One of the reasons for the SR doing this was that most of the ex LSWR lines headed straight into prevailing SW winds, also older locos generally had smaller diameter boilers and the air flow round them did not have such an adverse effect on the view from the cab.
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Offline PLD

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Re: Smoke deflectors
« Reply #6 on: October 11, 2014, 02:22:16 pm »
As has been said, the purpose was to deflect smoke by creating an airflow that carried the smoke away from the loco, thereby improving visibility for the crew.

It was found that in certain conditions the airflow made the smoke tend to 'cling' to the boiler of the loco.

There are so many different types of deflector because the air flow around every type of loco is different and the defectors are tuned (in size and shape) to be most effective for that loco.

The airflow around the loco is dictated by numerous factors including. the main ones being:
  • Speed of movement.
  • Shape of the boiler (length and diameter; also taper boilers in general had less need for deflectors).
  • Shape of the smokebox front.
  • Pressure of the steam at the chimney.
  • Position of chimney relative to the front end of the loco.
  • Height of chimney above the top of the boiler.

Generally higher speeds, higher preasure, larger boilers and shorter chimneys make the need for deflectors more likely.


BR days I think just the 9Fs curious eh ?
Plus 'Clans', 'Britanias' and the 'Duke' of the BR standard classes...

Basically all the more powerful classes...

Offline Newportnobby

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Re: Smoke deflectors
« Reply #7 on: October 11, 2014, 02:25:40 pm »
IIRC the Crosti boilered 9F's were particularly prone to drifting smoke yet never had  smoke deflectors fitted (he said, prepared to be shot down in flames)

Offline EtchedPixels

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Re: Smoke deflectors
« Reply #8 on: October 11, 2014, 04:17:45 pm »
Plus 'Clans', 'Britanias' and the 'Duke' of the BR standard classes...

Basically all the more powerful classes...

Except the GWR ones.

Smoke deflectors are a trade-off. Some designs got modified because the deflectors themselves can also restrict the crew view in some cases. It's another area with masses of variation to generally makes RTR model companies lives a misery 8) For example the Britannia class started with handrails on the deflectors which were replaced with grabs after the Milton crash in 1955. That was in part blamed in part on visibility problems caused by the handrails on the deflectors.



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Offline MikeDunn

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Re: Smoke deflectors
« Reply #9 on: October 11, 2014, 04:54:48 pm »
Basically all the more powerful classes...
Really ?

I don't recall A4's having them  ::)

Offline Dorsetmike

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Re: Smoke deflectors
« Reply #10 on: October 11, 2014, 06:25:01 pm »
Basically all the more powerful classes...
Really ?

I don't recall A4's having them  ::)

The shape of front of the A4s would probably have generated sufficient updraft  to preclude the use of deflectors.
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Offline PLD

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Re: Smoke deflectors
« Reply #11 on: October 11, 2014, 07:21:30 pm »
Really ?

I don't recall A4's having them  ::)

Plus 'Clans', 'Britanias' and the 'Duke' of the BR standard classes...

Basically all the more powerful classes...

I didn't realise the A4 was a BR Standard Class  ??? ::) :(

I always thought it was designed by some bloke called Gresley about 20 years before BR was formed...  :dunce:

Offline MikeDunn

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Re: Smoke deflectors
« Reply #12 on: October 11, 2014, 08:19:22 pm »
Well, you did separate the comment I quoted from the part you emphasise now ...  ::)
Basically all the more powerful classes...
Really ?

I don't recall A4's having them  ::)
The shape of front of the A4s would probably have generated sufficient updraft  to preclude the use of deflectors.
I seem to recall (not from personal experience  ::)) that early wind tunnel models didn't clear the smoke properly ... however, when someone left a thumbprint on the model, this did cause the smoke to clear.  I think this was on the A4 - can anyone confirm, or instead say what class it was ?

Offline Bealman

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Re: Smoke deflectors
« Reply #13 on: October 12, 2014, 09:31:46 am »
IIRC the Crosti boilered 9F's were particularly prone to drifting smoke yet never had  smoke deflectors fitted (he said, prepared to be shot down in flames)
Wasn't the smoke outlet/chimney half way down the side of the boiler on Crosti 9Fs?
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Offline port perran

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Re: Smoke deflectors
« Reply #14 on: October 12, 2014, 10:39:44 am »
I have a picture in one of my books of a non-crosti 9F running without smoke deflectors.
It's amazing how much more rugged it made the locomotive look.

By the way, I may be wrong but did the A4s (or some of them) actually have very tiny deflectors fitted either side of the chimney ?
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