…“Stressing the main rod and bearings”…Wouldn’t the rod assembly be disigned to withstand the force put through it to the point of losing adhesion to the rail…? Either by force of the power out of the piston or force coming from gravity driving the wheels…
QM
I’ve been told by a few steam engineers that trying to use the reverser to slow the train was highly discouraged by the RRs because damage to the main rod and even the cylinder heads could occur. Apparently as well engineered as they were they could still be damaged by high speed reversals or sudden stops due to water in the cylinder.
I would like to see the main rod under load with a strobe light. I’d almost be willing to bet that the main rod bends into an S shape from the loads.
Mike
I’ve alwasys been amazed the rod stays in place when you see a steam engine running at speed…The rods are flying around with so much speeed I just can’t imagine how the pin at the wheel supports that loading. I understand the counter weight on the wheel pretty much balances the whole assembly, but certainly the loading on the support pin at the wheel doesn’t have balanced loads.
QM
I’ve always wondered how the main rod pin could take the inital push or pull at start up. I guess that’s why they are built so heavy.
Yet, I know they have to flex. More then people would belive. Once you’ve seen a connecting rod working under a strobe light you have a whole new respect for mechanical dynamics. It’s a wonder some things don’t rip themselves apart.
Mike
Just watching the mechanical workings of a steam engine of what has to happen…Pieces sliding together, large weighty pieces rotating at the same time they are under much stress from force being put through them, rotating parts…and some of these parts are of a very weighty nature. Plus the piston assemblies doing what they do…Valves moving and levers going through movements to move another part and at the same time that part rotating on a pivot pin…and perhaps more I haven’t mentioned…Bearings doing support work…So, all this is happening at a rather rapid pace as the engine is working down the line…and not to mention what has to happen to produce the steam that is moving all these parts…I wonder how a steam engine had much durability at all…Just seems there were so many potential areas of mechanical stuff to fail. But I know they did the job over the “roads” for a century plus. Of course some better than others.
QM
That’s very true, but the RRs had a known length of service for each engine. They knew how far they could run and than switched the engine for a fresh one because more than likly they needed to clean the flues and pull the cinders out of the smoke box not to mention grease and oil and what ever. That’s why the RRs had so many steam engines. That’s also part of the reasn why the diesel caught on like wild fire.
But I must say that the same forces are still present in the diesel just unseen and much better balance for too.
In my book nothing beats the steam engine for raw brutish power. Imagine 6000+ hp out of two cylinders. Just now that mark has been reached with one engine, but with 16 cylinders.
But, the steam engine had to go and sooner or later the diesel will be gone too.
In case of downhil the operation of the steam engine is rather uncontrolled. The steam engines are disigned to be driven by steam in the cylinders, not by the rods and wheels. For that reason those forces where mostly uncontrolled and could be much more higher than in normal operation. Ringhoffer invented his system for cog railways, also with infinite adhesion (the cog wheel cannot slip).
If for some reason you replace the steam in the cylinder with fresh air, the first problem is what happens when it includes also some water (usually does) and under high pressure in the cylinder (by rods) it will reach the saturation earlier as the piston reaches the endpoint - no movement is possible after this point an either the rod or the crank pin or the frame will crash. In normal operation we can very exactly control the air pressure in the cylinders (which cannot be higher than the pressure in the boiler).
The another question is the lubrication and the temperature of the cylinders. All this points were designed for normal lubrication under normal steam pressure, in reverse (downhill mode) the pressed air can reach much more higher temperatures as the overheated steam from the boiler. This means the oil can loose it lubrication parameters or will be pressed out from cylinders by the high pressure air.
Those question were the reason why this operation was not very popular among the constructors of steam locomotives.
…From what you are saying then, there must be no “combustion chamber”…between the piston and pistion “head”. In other words, when the piston is at it’s maxium position towards the cyl. head…hence causing a hydrostatic lock if water would enter into the cyl. with the “air Pressure”, when causing it to act as a brake.
I have never seen the action [maintenance], where lube oil is added to the engine…Must be at some time as you are saying I’m assuming, lube oil is inserted along with the steam in normal operation. Where is this lube oil stored on an engine…? How often must a piston and Cyl. be rebuilt…?
QM
Hi QM,
The piston doesn’t bottom out in the cylinder but the volume can be taken up by water which could blow the head off that’s why the engineer would open the cylinder cocks at startup thus blowing out the water that dropped out of the steam while idle. On the older steam engines the cylinder oiler was located in the cab on the boiler, the newer engines had an injector above the valves run off a crank. The oil was made from tallow as that was the only oil able to take the high temps.
I don’t remember off the top of my head but I think that 300# of superheated steam would be at about 500 or 600 degrees F.
Mike
Lots of good info Mike…Such complicatons. One wonders how the builders thought of all this stuff early on in building these monsters when they were in their infancy.
Yes, as you mention, I understand the steam flying out of the cyl. cocks when an engine starts out.
[I’ll be away from our forums until Friday]…
QM
Hi QM
the overheated steam temperature is in Celsius grades 300-420.
The lubrication was done on different ways. With mechanical lubricator (driven by rods - on BigBoy with a chain) or hidrostatic lubricators. Both lubricators lubricated the pistons, valves and cylinders. (you can see tinny cupper tubes around the cylinder, where the oil was pressed into the system.
The lubricators also oiled other moving parts (rods, crank pins etc.)
I can tell you from my own personal experience as a steam locomotive engineer that, oh yes, there definitely is a way to brake using the reverser (A.K.A. Johnson Bar). I used to be an engineer on the Cedar Point & Lake Erie, which is a steam powered 3-foot narrow guage railroad at Cedar Point Amusement Park in Sandusky, Ohio. Most of our engines didn’t have any braking system at all, though one had a steam brake. We were forbidden from using that steam brake. Air brakes were non-existance on all of our equipment. To do any braking at all, we would first open up the cylinder cocks and then bring the reverser all the way back. Then we’d nudge the throttle just barely enough to get a whisp of steam to the cylinders. It didn’t take much pressure to send those drivers spinning backwards. And no that doesn’t cause a derailment. Atleast we never experienced that. And we kids did some serious goofing around on that railroad. But you definitely want to back off that throttle right now and throw the reverser in the corner (all the way forward) if you had spent to much steam and caused the drivers to slip backwards. The locomotive shakes and lurches quite violently and the wheels will spin out of control at extremely high speed with just a little too much throttle when the reverser is all the way forward or back. If that happens, throttle off!! In fact, you need to practice throttle modulation rather than constantly pulling back on the throttle when braking this way. Soft nudges on the throttle is all you need. Nudge it open, then close the throttle immediately. Repeat if necessary. You feel the deceleration by the seat of your pants. Notice what the wheels are doing; listen to the stack talk. There are four chugs per revolution of the driving wheels. That chug-chug-chug-chug will speed up and get louder if your drivers are slipping in either direction. It doesn’t take much to slow the train, but it does take time. Allow enough time to utilize your braking power. The CP&LE has friction bearings, so w
Thanks Jon B…I started this thread by asking the braking question and you finally seemed to answer, yes it was possible with extreme caution. It seemed to me with the steam always available and the engineers control over the valving…that surely some braking power could be generated by controling the valving, and steam and of course you mentioned the all important opening of the cylinder cocks. From your discription it sounds critical that each of your moves were accomplished in the right amount and order.
How did the builders of that engine expect one to stop it when you were moving it just as itself…?
QM