is there such a thing as steam horsepower because they always talk about the tractive effort and how many pounds can equal one horsepower?
not sure of a converstion from TE to HP but yes steamers can have HP ratings…usually at the “drawbar” meaning at the tender knuckle…they can also have a HP rating at the drive wheel…for example the PM 1225 in Owosso Mi …a Lima SuperPower Berkshire has a HP drawbar rating of around 4000hp…a UP Bigboy is around 6300 dbhp…naturally these figures would be approximent because power curves just like an infernal combustion engine… based on load and speed
and like with cars…Torque(TE) gets you moving HP keeps you moving at speed
There are two ways to measure HP.
One way is to have a dynamometer car – that one actually measures pounds of drawbar force and feet-per-second of forward speed, and pounds force times feet-per-second gives foot-pounds/s, a unit of power, times a conversion factor gives HP.
The other way is from an indicator card. This rather clever measurement technique goes back to James Watt. You hook some kind of measurement device to the steam cylinder and crosshead to get a plot of cylinder pressure as a function of crosshead travel. The result gets graphed on a card or sheet of paper, and the area within the pressure-stroke curve for a complete cycle is the work done per engine revolution. Allowing for revolutions per second, this gives what is known as indicated HP.
Somewhere between the steam doing its thing with valve admission events, strokes, and exhaust back pressure, which gives the indicated HP, and the dyno car, which gives drawbar HP, are all of the losses from bearings, connecting rods, crossheads, wheels, the weight of the tender, etc, etc. Generally the indicated HP is considerably more than drawbar HP on account of where HP gets used to turn wheels on both the loco and tender.
True. But you sometimes see HP “ratings” for steam locomotives that weren’t measured at all-- just calculated. So there are more than two kinds of so-called “horsepower”.
IIRC, a steam locomotive’s horsepower can vary with how hard the boiler is working. I remember someone saying that a steam locomotive reaches its horsepower peak when the engine is using steam as fast as the boiler can produce it. (And there is such a thing as boiler horsepower as well.)
But in practical terms, tractive effort was more important with steam engines, because if the locomotive could start a train, it could pull it. Horsepower during the steam era only became important when the Super-Power concept of power at speed was introduced in the 1920s and 1930s.
People used that expression, but that so-called “horsepower” was usually (or always) just a calculated (not measured) estimate of the engine’s potential power. Before the engine was built, the customers were trying to guess how powerful it would be-- so they’d figure so many square feet of heating surface, and so many pounds of steam per hour per sq ft, and so many pounds of steam per ihp-hr. But they knew it was just an educated guess.
To elaborate just a bit, boiler HP was based on the amount of steam a boiler could produce in lbs/hr (calculated/estimated) and was divided by a factor based on the lbs of steam per indicated HP or per drawbar HP.
For example if a boiler could produce 100,000 lbs of steam (a relatively high figure for a 4-8-4)and the estimating factor was 21 lbs of steam per IHP (a figure Baldwin used), then the boiler hp would be 4,761. It would be up the the steam circuit and machinery design to make the best use of the available steam.
The estimating factor considers boiler pressure and degree of superheat. The higher the BP and superheat, the lower the factor. It’s pretty conservative, because some locos could get into the 16-17 lbs/indicated HP range during tests.
Lima’s Alleghany reportedly got 9LBS\IHP…boiler HP was est over 10,000…but we will never know
Do you recall the source for the 9 lbs/hr steam rate?. Surviving Allegheny tests from 1943, 1948, 1951 and 1952 (originals at C&OHS archives) don’t show any ratio of IHP vs steam rate. However, they do show that the steam rate per DBHP is in the 21 range with 160 loads, Russell KYto Columbus OH (Test nos 100, 102 and 104).
FWIW, the PRR T1 posted the lowest water rate recorded, varying form 13.6 to 13.9 lbs/IHP at 66 to 76 mph (Altoona Test nos 1428, 1436, 1439, 1447).
this is from info supplied by the Henry Ford Museum " steam mechanic on duty" when i visited there last summer using the standard formula heating surface (both firebox and superheater) injector\feedwater supply and coal feed rate…granted with a grain of salt account theyve been wrong before…i also seem to recall something in Trains mid 90’s?? about the Alleghany’s weight\power and the “indiscretions” by both Lima and C&O…Lima and C&O alledgely “conspired” to reduce to weight so engineers didnt get full pay for the weight on drivers which is how they were paid in the steam era as well as “boosting” the power output of the boiler"…for advertising purposes"…
its not my intention to spread bad info…thats why i put it here…ya’ll know more then me and i look forward to corrections[;)][D)]
Thanks for the info. I’m always curious where some of these numbers come from. If the lbs steam/IHP ratio falls much below 14.0, I start asking questions. Too bad such a well-known museum is spreading this type of misinformation. I often wonder if the museum staff actually researches and controls the scripts, or if the docents are left somewhat on their own. If the Ford Museum can’t get it right…
Each pound of steam in to the cylinder is about 1400 BTU, depending on superheat and feedwater heat recovery. Each HP-hr out of the cylinder is 2545 BTU. !4 lb steam/hp-hr is 13 percent thermal efficiency. The thermal efficiency of steam locomotives was supposed to be well below 13 percent – 11-12 was supposed to be a peak achieved by Porta while 4-6 was supposed to be typical in operation. For the real-world thermal efficiency, you have to figure in boiler lagging heat loss, combustion inefficiency, mechanical losses between the cylinder and the drawbar.
But Super Power steam reaching 13 percent indicated efficiency (the 14 lb steam/hp-hr) sounds about right for their optimal operating conditions.
Felton and Paul are making my head spin with all of this high math.[%-)]
Now, let me get my hand on those throttles and the seat of my pants will tell you the answer![;)]
lol…no kidding…shovel on a lil more coal throw the johnson in the corner and put it in the kitchen
FYI… my copy of “The Steam Locomotive” gives the formula for HP= (Tractive Effort in lbs x Speed in MPH) / 375. A dynamometer car will give measure both of these parameters to calculate the HP. The tractive effort has to be measured at the speed used in the formula - if you use the Starting Tractive Effort and multiply by the top speed of the locomotive, you will have a grossly inflated figure!
Hope this helps…
James
thx
In case it wasn’t clear, he means a pound of steam entering the cylinders contains ~1400 BTUs more than a pound of liquid water at 32 degrees F. It contains something like 250 more BTUs than a pound of steam at 212 degrees, atmospheric pressure.
Gee howd they git all them there horses hooked up to the engine ?[:-^] sorry the hillbilly coming out in me. Couldnt help it [oops].
There are some old Trains articles written by a “tallowpot” explaining that there is a whole lot more to firing a steam locomotive than simply scooping some coal on to the grate – unless of course you want a clinkered mess and the engineer glowering at you or worse as the steam pressure gauge starts tapering off towards zero.
These locomotive firemen knew too well which locomotives required you to shovel and shovel until your back ached, and which locomotives “steamed well”, meaning you could get a lot of steam and keep the pressure up without having to work yourself to exhaustion. On that basis alone, locomotives must have varied a great deal in their efficiency of turning coal into steam and into tractive effort.
this is true…hand firing any boiler is an art form that is slowly dieing…the color of the flame…the sound…ammount of draft…etc etc all plays a role…ive fired a steam traction engine during local Threshing festivals and its a talent…one that i havent mastered yet lol…even with “automactic stokers” the scoop was still important to maintaining proper steam…as well as knowing your territory and your hogger…and leave us not forget the rest of the firemans job…running his injector\feedwater…lubricators…and other things both in route and when stopped