D51 498 gets a new set of smoke deflectors

[bikkuri bahn]

Takasaki based D51 498 was recently fitted with extra large smoke deflectors.  The deflector style, called the "Gotou Type", was previously produced and fitted to D51 types at the JNR Gotou Works (Yonago) and Takatori Works (Kobe).  The model for this installation was 498's sister, D51 499, which operated on the Kansai Main Line.  This heavy duty deflector type was installed in preparation for planned running on the heavily graded and tunnel-rich Chuo Main Line between Kofu and Kobuchizawa from late May through early June.

 

*I quite like its appearance, it makes the D51 more burly looking than it really is.

 

Photo gallery:

http://www.asahi.com/travel/rail/gallery/100428d51/

 

More pictures, including a 1972 shot of number 499 at Tsuge on the Kansai Main Line:

http://rail.hobidas.com/blog/natori/archives/2010/04/26hi.html

[stevenh]

It really is a beautiful engine... what exactly do deflectors do? Make sure the smoke only goes upwards? I would've thought there'd be enough pressure from the firebox for that... 'deflect'ing smoke doesn't really make sense, unless it's from the pistons.

 

Either way, also, why are they especially required for tunnel-rich lines?

 

I do wish I'd seen an active D51 when I was over there... those images are perfect, in the dismal lighting too!

[Martijn Meerts]

It didn't just get the bigger side smoke deflectors, but also one on the chimney itself.

 

Their function is to lift the smoke when the trains run at higher speeds. Especially newer locomotives are efficient enough not to require large amounts of pressure, so the smoke doesn't really get spit out anymore. The deflectors make sure the driver can actually see straight ahead without problem ;)

[marknewton]

Steven, I could go on endlessly about steam loco smokebox/front-end design, having spent my fair share of time working on and in them - including  locos like 1210 and 3026 - but I'll try to keep it simple.

 

Older locos had simple, single-orifice blastpipes located high in the smokebox. They relied on a small, high velocity jet of exhaust steam from the cylinders to create draft in the firebox. This meant that the exhaust steam and combustion gasses would leave the top of the funnel with some pressure, so the smoke and steam tended to be projected up and well clear of the loco when working steam. The disadvantage was that it lead to excessive back pressure in the cylinders.

 

Modern locos have low, multiple-orifice blastpipes, and the drafting is reliant on a large volume of exhaust steam at a low pressure. This leads to the smoke and steam trailing back into the cab and obscuring visibility for the crew. This problem is exacerbated by the tendency for a partial vacuum to be formed at the front of the loco by the flat front of the smokebox.

 

Smoke deflectors are perhaps mis-named, because they are intended to prevent the partial vacuum from forming, and to channel the exhaust up and over the engine by directing the airflow upwards.

 

The other gadget on D51-498 is truly a smoke deflector, it's designed to direct the exhaust rearwards in tunnels, rather than having it travel upwards, strike the tunnel roof and be dispersed aroound the cab of the engine.

 

Hope this helps,

 

Mark.