a steam locomotive is traveling 20 mph on and approaching level grade
what needs to happen to increase and maintain speed at 30 mph?
Take it to the backshop for repairs? If the throttle is fully open, I believe the cylinders are getting all the steam they can get. Kinda like if you’re driving your car with the accelorator to the floor and you’re only going 20 MPH. When starting the engine, the engineer might put the throttle fully open to get it started, but then back off as the engine gained speed.
First, you answered your own question - How to make it go faster: open the throttle and brakes off. (ofcourse you have steam or it wouldnt move to begin with)
However, you posted throttle wide open - I’d say just sit back and watch her go at this point. You cant open the throttle any more than WOT (wide open throttle).
When shes ‘over the shoulder’ (meaning throttle wide open) and “lever’s in the corner” (meaning full forward - no cutoff), you cant get more from a loco than that. If you cant move the train with all that… get a helper loco youve exceeded the tonnage rating for this one loco.
With the 6 points you listed, all you need do is spot your pocket waltham and count posts as they go by ( how engineers used to gauge their speed).
A#1 North!
PMR
(PS: you just dont WOT a steam loco. They must be coaxed to speed. Do so, you will most certainly spin the drivers, yank a coupler [which is all kinds of bad news], pound the rails, even blow a few pipe or piston seals. One must remember, even the sportier versions of steam locos must be finessed to speed. They arent race cars. And the only traction control steamers had was sitting in the cab. Dont forget shock control - [slack action] people and products dont like being slammed around. Ive heard steamers break cadence into din of exhaust noise even at a good clip. impressive, but detrimental. PRR T-1s are known for slipping, so much so I think it was part of their design. Very touchy throttles requiring almost a master of the art. You cant just throw it over your shoulder if you want to gain speed. In all actuality, your rear end does more
To echo what is already said - it seems the only way to go faster there would be to go downhill! There may be some situational environmental conditions that could effect stuff - if it is cold out you might need to open the cylinder cocks to let out condensed water in the pistons, if it is cold you may also check for wheel slip - you may need some sanding action. This is why it tended to be important for engineers and firemen to be used to their locomotives, there’s a lot of little things that they’d know or not know from experience about the situation to know why they aren’t hitting 30.
so you think the boiler is always producing the same amount of steam, as much as needed when running at top speed or up the steepest grade, and the throttle just limits the amount of steam needed when running at slower speed?
what happens to the excess steam that isn’t needed at lower speeds?
those are the conditions when the loco is running at 20 mph.
trains needs to be able to run at different speeds. this could be a passenger train capable of running a 80 mph that is moving thru a yard
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If the boiler is at max pressure, and the throttle is fully open, that means all of the steam the boiler is capable of producing (maximum pressure) is being used (let out through the throttle). If the boiler was under temperature, the pressure would be going down with open throttle, as there would be more steam exiting than being produced. If there was more steam being produced than there was being used, it would be gaining pressure. In this par
so are you suggesting that speed depends on boiler pressure?
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here’s test data showing that boiler pressure is roughly the same (near 200 psi) for various speeds: ~9, ~20, ~800, ~40 mp
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While this is interesting, I would note my qualifier relating to the boiler being at maximum pressure - unless we know the “red line” for this locomotive was 200 psi, this would not fall under that criteria. Most consolidation boilers ran around 215 psi from what I’ve read.
It’s like with your car - if you aren’t redlining, you can rev up more to get to a higher speed then settle into a similar RPM at that new speed, but if you are already redlining and aren’t increasing speed, you aren’t going to get any faster.
To be more accurate, changing speed depends on boiler pressure. To go faster, you’ll have an increased boiler pressure while accelerating, but it’ll settle back down when you return to status quo; the issue in your scenario is that you are already at maximum pressure.
i said “near” for a reason.
what would cause an increase in boiler pressure (other than closing the throttle)?
does status quo mean orignal speed or new (higher) speed?
i don’t believe the car analogies work here because motor rpm is directly related to speed.
the table shows that locomotive speed is not directly related to speed boiler pressure
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Watch the video that Ed posted earlier on valve gear. There’s actually 2 valves inline in the steam passages. One is the throttle/regulator. The next in line is the cylinder valve gear and valve. The throttle admits a given volume of steam to be used by the cylinders. The valve gear regulates the steam to the cylinders.
To start a train. The engineer first moves the quadrant to either forward or reverse, then opens the throttle. Like a manual shift car. Select first then gas. As your going down the track and you want to go faster, move the quadrant a little further. Once you are at desired speed, move the throttle valve to almost closed. Your still admitting steam but not the volume to go faster. Closing the throttle valve is like taking your foot off the gas while in gear but no braking pressure from the engine. Putting the quadrant in the center with the throttle closed is essentially like neutral. Opening the throttle with the quadrant in center can blow steam into the smoke box because of leaking cylinder valves. Not a good idea.
Pop valves are safety valves to keep the boiler pressure up to a certain level. A good fireman will try to keep them from popping off. That means he is wasting steam. Before a large use of steam he will add more heat and maybe shut down the injectors. When boiler pressure is almost to the valve setting he will open the injectors and add water instead of making steam.
Hopefully this explains it for you.
Pete
Sheesh, there is some wack stuff in this thread.
Standard operating procedure for ‘best thermodynamic efficiency’ has long been 'get the throttle fully open as fast as you can (to avoid throttling losses from the boiler/superheater to the steam chests) and then ‘drive on the reverse’.
Under the stated initial conditions, developed power is just balancing running resistance at 20mph. To ‘go faster’ you will lengthen the cutoff to increase the mass flow per stroke. This will draw additional steam from the boiler, which will cause a (relatively slight) drop in boiler water level. (And if the pops were getting ready to lift, they won’t then…)
Water level in the glass will drop and eventually require the injector or feedwater-heater hot-water pump to be actuated. Even heated feedwater is many degrees colder than the saturation temperature of the boiler water, so nominal pressure will tend to drop. On the other hand the additional mass flow of steam means additional mass flow in the exhaust… hence more draft, hence a brighter fire. (This is part of what the English call ‘automatic action’)
At some point, probably before balancing at 30mph, you will resume the ‘firing early and often’ that you should have been attending to at 20mph. A good fireman will estimate the additional fuel the engine will need at the new higher speed on the relevant part of the railroad… and fire and trim accordingly.
(Incidentally, the more correct way to start, if you are concerned with slipping/spinning – as in a PRR T1 with a heavy train negotiating a bunch of station switches with low joints and worn frogs – is to open the throttle only partway and ‘drive on it’. A slip then produces wiredrawing loss that more or less promptly exhausts the steam in the chests, in the same sense that a slipping LP engine on a Mallet quickly exhausts the receiver. And the slip stops, wit
There is an interesting quirk about reciprocating steam locomotives, which explains why big boilers and fireboxes/chambers are a key determinant of high speed capability. The ‘balancing point’ between steam generation and steam demand with the engine(s) in full gear, even with radical fixed cutoff like the 50% in a PRR I1s, would limit speed to a comparatively low number. So you shorten cutoff to increase how effectively the steam mass in the cylinder produces piston thrust – you let it expand and do work, rather than blow a cylinder still full of pressurized steam wastefully to exhaust.
But eventually you’ll reach a point where the decreasing steam mass going into the cylinder in a given admission no longer produces acceleration. To go faster, you need to start lengthening cutoff again, which of course requires more mass flow out of your boiler.
Now, plenty of ‘fast’ engines run into a wall of pain at this point because their steam tracts or valves are incapable of handling the increased necessary mass flow in the shorter and shorter interval that admission occurs per stroke. The ATSF 3460 class, with a ginormous boiler and 84" drivers, could easily run 100mph on the relatively flat east end. But it could barely reach 105mph under the best conditions… valve limited. The C&NW E-4b, another monster Hudson, couldn’t even crack 100mph with the AAR test train in 1938.
Engines not so limited turn out to have an interesting statistic: the English A4 Pacific, the German BR 05, and the N&W J all made their fastest road speed with cutoff in the lower 40s
Greg) “…so are you suggesting that speed depends on boiler pressure?”
Yes, that and volume. Pressure AND volume.
Pressure = The force you can throw at the work load. (if you dont have psi, you cant turn the wheel over once)
Volume = The amount of time you can continue that work load. (if you dont have volume, you cant turn the wheel over a second, third, of fourth time)
“… the table shows that locomotive speed is not directly related to speed”
wait… what? That doesnt make sense. In any lan’guage’.
I wanna go back to your very first post. You said,
"you are doing ‘20’, throttle is ‘open full’, cut-off at ‘minimum’, brakes ‘off’, bpsi near ‘max’, fire and psi are ‘maintained’, … "
“what needs to increase and maintain at 30?”
First off, if thats your top speed at WOT then (full open throttle and boiler is ok you said), your either on an 0-8-0 with 25" drivers (LOL) or the Best Fr
yes and what determines the amount (lbs.) of steam produced?
i’m suggesting it’s capable of 80 mph
aren’t steam locomitives designed to run at different speeds, efficiently?
(what determines, not controls, the horsepower produced by a car)?
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as that table suggests, the engine is typically operated near max boiler. allowing full boiler pressure into the cylinders while the engine moving slowly and cylinder valve is opened for long periods of time is likely to cause slip.
while that table also shows the throttle open full, this is while running. my understanding is the throttle is just “cracked” to get the locomotive started to limit the amount of steam into the cylinders and the cylinder pressure. throttles are designed to have more finer control near the beginning of there range
the throttle is opened fully once the locomotive is running.
as the locomotive picks up speed, more steam is required to maintain the steam density/pressure in the cylinders (twice as much steam is needed at twice the speed).
while increasing cutoff may allow more steam into the cylinders and increase speed momentarily as more steam flows from the boiler, boiler pressure will drop … until a new equilbrium is reached, more likely at a lower speed
my understanding is cutoff is reduced to improved the efficiency of the steam of the engine
at the least, reduced cutoff allows greater boiler pressure to be maintain if not a greater amount of steam to enter the cylinder resulting in high
Greg) What determines the psi produced in a boiler? Holy cow any number of a million things, at any different time, under any number of a million circumstances.
thats rather an unfair question as there are so many ways to make steam psi. in a steam loco.
Ok, your loco is capable of 80mph. that tells me you have to have atleast 70" drivers. Having that size driver, and the fact it can do 80 tells me its a modern steam loco (90% chance). Being a modern loco tells me its prolly Superpower design capable of producing all the steam it can use, and a good chance of being superheated aswell.
Knowing this, plus your givens about throttle, boiler status, cutoff, and speed of 20mph, its safe to say your prolly spinning the drivers right now.
After you correct that and open the throttle again - more gently this time, your train should pick up speed.
sit back and count the posts you pass lineside against your watch your on your way to 30mph. Thats if you are doing 20 and JUST opened the throttle to full. Shouldnt take long if your train is of proper tonnage and your loco is up to snuff after you stop the wheel slippage.
However, if you pulled the throttle open about 10 miles back and your still doing 20…
Your definately doing it wrong. Hit alt-Q and reset your game.
What determines hp in a car? Again, that is such a can of worms
not pressure (PSI, lb/sq.in), mass (lbs)
so a steam engine can only run at one speed ???
does a car only generate a constant amount of hp? only runs at one speed?
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