Accurate Reverser Usage for Steam Engines

[mjlevy1118]

Hi all, I have a prototype realism question - when driving a steam engine, what are procedures regarding when to use the reverser vs how open the throttle is?

By that I mean if you're picking up speed and want to bring the reverser back toward center, are you supposed to shut the throttle off, wait for the steam chest to empty, move the reverser back, and then open the throttle again? Or would you able to move down the reverser regardless of how open the throttle is?

I know Smokebox's depictions of 1860s-era steam locomotives require the throttle to be closed and the steam chest nearly empty in order to adjust the johnson bar, or else it slams itself forward. But IRL, I don't know if locomotive technology progressed over the following 40 years so that doing so wasn't necessary by the early 1900s. I've watched real steam cab ride videos on youtube to see when the engineers choose to adjust the reverser, but the results are inconclusive. What do you advise?

[BNSFdude]

The way you operate the reverser and throttle is definitely dependent on the prototype you're working with. A lot of UK steam, and pre-modernization US steam had man operated reversers, and trying to operate it with steam being pushed from the throttle to the chest could cause some broken arms in some cases.

Modernized locomotive, say for example Mike's lovely 844, used power reverse gear which used air pressure from the MR to move it on input from the linkage. Think of it like power steering.

[mrennie]

Hi all, I have a prototype realism question - when driving a steam engine, what are procedures regarding when to use the reverser vs how open the throttle is?

By that I mean if you're picking up speed and want to bring the reverser back toward center, are you supposed to shut the throttle off, wait for the steam chest to empty, move the reverser back, and then open the throttle again? Or would you able to move down the reverser regardless of how open the throttle is?

I know Smokebox's depictions of 1860s-era steam locomotives require the throttle to be closed and the steam chest nearly empty in order to adjust the johnson bar, or else it slams itself forward. But IRL, I don't know if locomotive technology progressed over the following 40 years so that doing so wasn't necessary by the early 1900s. I've watched real steam cab ride videos on youtube to see when the engineers choose to adjust the reverser, but the results are inconclusive. What do you advise?

It depends on the maximum boiler pressure (and hence maximum steam chest pressure) and whether or not the reverser is power-assisted. If you look at the FEF-3, on the right-hand side underneath the running board you can see a big cylinder and piston - it's the power-assisted reverser mechanism (powered by compressed air, or by live steam in an emergency). Just like power-assisted steering in a car, the piston makes it easy to move the reverser despite the large effort that the reversing arm itself has to make to raise or lower the lifting links when there are strong forces acting against it coming from the valve gear in motion.

The AT&N Consolidation was built at a time when railroads were already starting to install power reversers, and in the plans for the Connie, that appliance was an optional extra. The AT&N didn't bother with it though, probably because the loco wasn't "superpower" (it wasn't superheated and had a relatively low boiler pressure). However, when I made the model of the Connie, I debated whether or not to simulate the reverser forces but decided not to, so as to make it easier to operate.

At some point in time, power-reversers became mandatory, probably because of the injuries and deaths caused by Johnson bars slamming into the engineers (I remember reading about one engineer who suffered a ruptured spleen and died after being virtually impaled by the reverser).

By the way, the reverser only slams when the instantaneous pressure in the steam chest is above a certain amount (it varies across each piston stroke, as the admission and exhaust valves in each cylinder open and close).

[mrennie]

The way you operate the reverser and throttle is definitely dependent on the prototype you're working with. A lot of UK steam, and pre-modernization US steam had man operated reversers, and trying to operate it with steam being pushed from the throttle to the chest could cause some broken arms in some cases.

Modernized locomotive, say for example Mike's lovely 844, used power reverse gear which used air pressure from the MR to move it on input from the linkage. Think of it like power steering.

We were writing our replies at the same time but you beat me to the Submit button

[BNSFdude]

Great minds, eh, Mike? Even used the same analogy.

[mrennie]

Great minds, eh, Mike? Even used the same analogy.

Yup