How did the tender coal pushers like in many USRA tenders and DM&IR 2-8-8-4's work?
oldline1
Simply a steam piston mounted to a crosshead and guide that pushed a wedge-shaped "plow" under the coal load at the slope sheet. Additionally, there were two arms or links that attached to a flat bar across the bottom of the stoker (if equipped) trough area.
Coal-Pusher by Edmund, on Flickr
The operating valve was spring loaded to return the cylinder and be ready for the next push.
Regards, Ed
Another picture worth 1000 words is diagram 83 in the ATSF form 2500 (from 1942) and the accompanying discussion on pp.175-176. Find the relevant section here for download:
https://sfrhms.org/wp-content/uploads/2019/08/SteamLoco-5.pdf
(You can get the whole thing by replacing the "5" in this URL with 1 through 6 for all the sections... all sorts of useful information in there.)
Here's a patent for an improved version of coal pusher with some useful discussion.
https://patentimages.storage.googleapis.com/d9/de/a0/f22e99783c19db/US1708507.pdf
Thanks for the info.
Must not have been a very good idea considering the number of tenders seen with them.
oldline1Must not have been a very good idea considering the number of tenders seen with them.
Depends on a number of things.
As tenders became larger, the potential danger of having to 'trim' coal from the back, perhaps at speed, to the gates at the front began to increase. The pusher was a mechanical way to accomplish this, and it became more important on engines with early stokers (which among other things could easily jam if too much coal was pressing on the feed 'worm') Still later, in the era where plates might need to be installed or removed over sections of very long worms, with many tons of coal loaded, the pusher could become still more important. It is difficult to imagine some of the larger tenders without some method of moving coal from the rear to the front; by the time you get to the proposed New York Central 64-ton 'no fuel stop' tender proposed for the C1a duplex, it's almost impossible to conceive working the engine without some controlled way of moving the coal at the rear of the bunker to where it would feed reliably.
When determining the best 'slope' for the slope sheet, there's something of a tradeoff between bunker and cistern capacity, and both the 'rank' and moisture content of the coal factor into how easily it will slide. Some of the "work" of moving the coal is done by vibration and train movement, but not all; as speed increased, the job of trimming could become more dangerous. Presumably railroads might be able to use some forms of cheaper fuel -- this is one of the timeless topics in steam-locomotive "economy" over the years.
One problem with coal pushers, of course, is that they caused increased trituration (in-situ grinding) of the coal around the rams. To some extent this might help with stoker feeding, but it would also contribute to fines carryover in firing, dirt, and other things. Again the type of coal fired would affect how well the system would work.
Toward the end of the first great die-off of steam in first-generation dieselization, the AAR and other organizations tried to advocate better fuel with better preparation -- a general aim being fuel of reasonable rank, well-washed and classified, with lump size about 2". You can get a good idea about this reading trade publications from about the 1948-1950 period. This fuel would feed more reliably, and perhaps 'crumble' less in handling.