Draft plates

[dnevil]

I found an interesting animated training film by Santa Fe on the components of a steam locomotive.

https://www.youtube.com/watch?v=QYNRhL0ddDQ

It featured a part I've not heard of, namely, "draft plates". They are pointed out in the attached image from the film.

What is the purpose of the draft plates? Has anyone implemented them in a live steam locomotive?

Daris

[Bill Shields]

makes cleaning the flues very very difficult on a small loco...to say nothing of cluttering up what is usually an already horribly cramped space.

cannot say that I have ever seen them..but then...

[Fender]

From my experience burning coal, cinders tend to accumulate below and in front of the front tube sheet. Perhaps this “baffle” would tend to increase the gas velocity there, scour away the accumulation of cinders, and direct them toward the front of the smokebox.

[Glenn Brooks]

Daris,

Very timely question for me. I actually have draft plates on my antique Campbell 4-4-0 (circa 1904) loco. Just looked at them a few days ago when I started stripping the lagging and plumbing off to test the boiler. Apparently these were standard equipment on full size locomotives. I didn’t know the proper name, but assumed they functioned to create more swirling motion in the smoke box, and also disrupt cinder flow out the stack. Which apparently they do, according to your post.

Now, one other feature my smoke box has, is a cinder screen mounted at the top of the draft plates, and extending all the forward to the front of the smoke box. The positioning of the plates and horizontal screening would completely block any cinders from rising to the top of the smoke box. They would fall down to the bottom, and assumedly collect in the front of the smoke box.

As another poster said, they do make it impossible to clean the flues from the smoke box end.

Here’s a pic of the plates mounted in my smokebox. Hard to see, but look towards the rear.

Note: the smokebox and boiler are 14” diameter. Fire tubes slightly over 1”.

BTW, I have no idea how this affects operation of a miniature loco, as I have not yet fired or run it. In fact, I’ve determined the loco has never been operated, since being built in 1904 - spent all its life on a stand in Al Campbell’s shop. (He passed in the late 1950’s). And not run since then.

As he was a master RR machinist and machine shop foreman on the NY Elevated Railway, with 50 years of service, so I assume he felt the plates and screening were an advantage. I can definitely see how they would increase flow in the smoke box. The U shaped exhaust motion in the video seems to indicate exhaust would need to travel 2 or 3 times as far, down and up around the plates. So maybe they also acted in a manner similar to a Venturi; increasing exhaust velocity up the stack, and improving fuel air mixture in the firebox.

I’d certainly be interested in hearing from others, who may have these mounted in an operating loco.

Thanks for posting the video and question!

Glenn

[daves1459]

I believe I can shed some light on the draft plate also sometimes called a smoke box baffle. When an arch is fitted into a fire box the hot gases pass over the upper edge of the arch and along the upper surface of the fire box or crown sheet just as intended. However, with out the draft plate these gases tend to enter mostly the top flues and then out the stack. With a properly placed draft plate the vacuum created by the exhaust blast is more evenly distributed across all of the tubes and flues and thus more evenly distributing the flow of hot gases and improving the boiler thermo efficiency. Often the draft plate was angled from it's top into the smoke box at such an angle to improve the draft through the bottom tubes. The draft plate was then made horizontal past the top of the exhaust nozzle into a larger chamber at the bottom front of the smoke box. Being a larger chamber and the sharp right angle bend to get out the stack the hot gasses tend to drop cinders at the front of the smoke box where the clean out hole is located in the smoke box bottom. In this way the cinders are in the bottom front of the smoke box and no all over everywhere.

Drafts plates are not very practical in a coal burning model for the reason already pointed out. I.E.: Flue brushing. However for a propane fired boiler where flue brushing is not needed the draft plate can be useful. Attached are photos of a draft plate I fitted to my Disney 4-4-0. It has a rather small boiler and I was trying to squeeze all the steaming out of the boiler I could. There is an arch in the fire box, turbulators in the tubes, and the draft plate in the smoke box to even out the draft on the tubes. It all seems to work as the boiler steams very well.

Dave

[Glenn Brooks]

Dave, well said! Very nice description also. Makes a lot sense re: improving draft through the lower flies...

Thanks,
Glenn

[dnevil]

Thanks to all who replied!

Daris