Rwy Age Gazette 29 March 1912 has an article on SFe's new dynamometer car 29-- one million pounds capacity it says:
"The dynamometer is of the double diaphragm type, recording both drawbar pull and drawbar push. The lever arms, with a ratio of five to one, are connected at one end to a filler block in the drawbar yoke and at the other end to a double piston, 20 in. in diameter, whose heads press against blind rubber gaskets, covering the liquid chambers. The piston is suspended by means of knife edges, in order to eliminate all friction. The bearings for the lever arms are small hardened tool steel pins surrounding the main pins. A mixture of glycerine and alcohol is used in the liquid chambers. These latter are connected to the recording apparatus and gage board by 3/4-in. copper pipes."
Looks like the levers are vertical, about 3 ft long, pivoting around a transverse axis, with their long ends connected to the piston.
I don't know how many railroads actually owned dynamometer cars, but I know that the N&W did. There is one preserved at the Virginia Museum of Transportation, home of soon to be operating N&W 611. Here is the page: http://www.vmt.org/Loops-Collections/Additional-rolling-stock/NW-Dynamometer-Car-514780.html.
Probably most of these cars were owned by and available for use from the locomotive building companies. N&W built their own. PRR may have had one, too, since they were a major builder also, although their big stationary one in tha Altoona shops probably did most of their testing. EMD and most likely GE still operate cars like these for modern diesels.
Thanks, BigJim. When I saw rotorhead1871's question, I thought of the dynamometer car and the (what I call) the standing dynamometer--but I was not in a position to answer, and certainly not able to provide the detailed information which you presented.. You produced evidence that the wheel has been invented; it may yet be possible to improve upon it.
Also, my Locomotive Up to Date of 1920 has a discussion of the engine indicator. Dynamometers are not included in the book, perhaps because such would not ordinarily be maintained in locomotive shops?
Johnny
rotorhead1871 interesting, how did they work? as a true dyno can absorb the output of an engine and convert it directly to kilowatts to get the true shaft HP, but in a locomotive, that would be hard as there is no shaft, just the drivers.--so everything would be moving....could they handle the complete output of the engine?
interesting, how did they work? as a true dyno can absorb the output of an engine and convert it directly to kilowatts to get the true shaft HP, but in a locomotive, that would be hard as there is no shaft, just the drivers.--so everything would be moving....could they handle the complete output of the engine?
Read this: http://mikes.railhistory.railfan.net/r062.html
.
rotorhead1871what we need is a dyno big enough to test these monsters!!...now that would be a setup!
The PRR Q2's "horsepower" is actually indicated horsepower (IHP) which is measured in the cylinders. It will always be higher than DBHP which is measured at the back of the tender. Of course, PRR had its own wrinkle in the horsepower game. The test plant in Altoona gave locomotive drawbar horsepower, which is measured at the rear of the locomotive and excludes any resistance involved in moving the locomotive or tender. This type of horsepower is somewhere between IHP and DBHP.
Fun with numbers.
The 7,498 DBHP "rating" for the Allegheny is, as timz states, a momentary/peak reading which was achived while the test train was coming out of a sag. This will tend to overstate the reading to a degree. The overall curve established for the H8's can be found in Gene Huddleston's book, The Allegheny Lima's Finest, pg 204. It shows that a more reasonable maximum reading would be about 6,700 to 6,800 DBHP, depending on how you interpret the scatterplot of DBHP and its corresponding scatterplot of DB Pull on the same page. The direct and indirect heating surfaces for the H8 boiler were larger than the Big boy, so even with the lower working pressure, the H8 could evaporate more water per hour, thereby producing more steam for the cylinders to use.
All things put together, the Big Boy could be reasonably expected to produce about 6,200 to 6,300 DBHP if required over-the-road, but the H8 could do more at about 6,700 DBHP or so.
thanks for all your help Tim, as you show above, reality can depart from the theoretical pretty quickly and it gets more strange. The big take away for me is that these were really big, powerful locomotives.....and that is cool....
thanks again, Phil
interesting stuff.....these machines are very interesting and I appreciate your comments.
rotorhead1871this whole world of HP calculation is a bit fuzzy!
So, just for amusement, try your thresher formula on a 2-6+6-6. If you assume 50% mean eff pressure in the cylinders at 250 RPM (i.e. 49.8 mph) that comes out to 8615 hp in the cylinders. A bit high, but not ridiculous.
But with a 4-8+8-4, 50% MEP at 250 RPM means 10740 hp in the cylinders, and no one would say that was possible.
Any engine with a high calculated TE will look powerful with that formula-- the big IC 2-10-2s come out to 7854 cylinder horsepower (cylinders 30 by 32, drivers 64-1/2, boiler pressure 275 psi says 10/48 Trains.)
rotorhead1871 ...if steam engines are rated at zero rpm...its all about pressure, and piston area/displacement? correct? ...given the bb has bigger pistons, higher head pressure....bigger stroke......how is the allegany rated at such a higher HP?? all you mechanical engineers....get back to me please...
...if steam engines are rated at zero rpm...its all about pressure, and piston area/displacement? correct? ...given the bb has bigger pistons, higher head pressure....bigger stroke......how is the allegany rated at such a higher HP??
all you mechanical engineers....get back to me please...
Steam locomotives produce their greatest tractive effort at low speeds, but their maximum HP at higher speeds. So a steam locomotive is not "rated at zero rpm" if your interest is how much HP the boiler can produce. Stationary, the locomotive produces no HP. As soon as the drivers begin to move lifting some tonnage behind the locomotive, when the 'cut-off' is set to the highest setting, the torque about the driver axles is the highest (I think...someone can correct me...)
Most steam locomotives produce their highest rated HP somewhere between 40-60 mph, depending on the driver diameter and how fast it is running. Also, the cut-off setting increases the efficiency of a steamer running freely at speeds in the upper quartile of its speed range, to the maximum speed permitted by physics, metallurgy, lube, and the trailing tonnage. Just because an engine is moving quickly doesn't mean it is running as much steam out of the boiler as possible without losing pressure. In fact, quite the opposite...a steamer is likely to use the most steam lifting the tonnage from zero because that is where the valve cut-off is set highest (meaning the valve travels in such a way inside its cylinder that it leaves the inlet port open the longest, allowing the most boiler heat to enter the cylinders). It should be noted that the first several laboured revolutions of the drivers at start-up include open cylinder cocks to eject condensate from the cylinders...even more steam loss! As the train gains speed, the engineer shortens the cut-off so that the valve only lets steam in for 60% of the piston's stroke, and then down to 50%, 40%, and eventually down to about 15-20% cut-off for engines with drivers churning at about 4-5 times per second, or about 240 rpm.
rotorhead1871"This [mean effective] pressure [in the cylinders] can be measured only by means of the steam engine indicator but we can assume a value which approximates the correct one. This we will take to be 50% of the boiler pressure."
BaltACDElectrical motors generate their most power and torque at zero RPM
timz rotorhead1871 You're thinking of calculated tractive effort-- 135575 pounds for the UP engine and 110200 pounds for the C&O. Nothing to do with power, which at zero RPM is zero horsepower for any engine. The 2-6+6-6 supposedly peaked at a momentary 7500 dbhp at 46 mph, and the 4-8+8-4 did 6300 dbhp around 40 mph. Neither of them could come close to their maximum power at low speed.
rotorhead1871
You're thinking of calculated tractive effort-- 135575 pounds for the UP engine and 110200 pounds for the C&O. Nothing to do with power, which at zero RPM is zero horsepower for any engine.
The 2-6+6-6 supposedly peaked at a momentary 7500 dbhp at 46 mph, and the 4-8+8-4 did 6300 dbhp around 40 mph. Neither of them could come close to their maximum power at low speed.
Which is a characteristic of every reciprocating engine. Your internal combustion reciprocating engine in your car develops it maximum power several thousand RPM above zero, and likewise develops zero power at zero RPM.
Electrical motors generate their most power and torque at zero RPM with decreasing levels of both power and torque as the motor's RPM increases.
Never too old to have a happy childhood!
that is well and good but: I found this in a discussion group and it clearly rates HP based on boiler pressure, bore/stroke/rpm...now the b/b engine stats are bigger than the allegenahy...but the boiler of the alleghany is bigger...although a lower pressure 250 psi vs 300 psi.
so my next question is at what rpm does the b/b run out of boiler (ie the boiler cannot maintain pressure at full stoking)....vs when does the allegehany??..it seems that since design speed for the b/b was 80 mph.....then the boiler will maintain pressure at 80 mph at what driver RPM?? since the b/b had bigger drivers....then where does that leave the need of the bigger boiler on the allegany ?? if the top speed was less...the b/b has a bigger bore and stroke and higher pressure....therefore the alleghany cannot deliver hp at a given RPM......
THE HORSEPOWER OF AN ENGINE
The unit of power is a "horsepower" and is defined as the amount of power necessary to raise 33,000 lbs. one foot in one minute. The horsepower of an engine is equal to the total pressure on the piston multiplied by the number of feet it travels per minute and divided by 33,000.The total pressure on the piston is equal to the area in square inches multiplied by the pressure per square inch, and this pressure is not constant but varies, being nearest boiler pressure during the early part of the stroke and decreasing after the point of cut-off is reached, as the steam expands to fill the space back of the piston, until the end of the stroke.This pressure can be measured only by means of the steam engine indicator but we can assume a value which approximates the correct one. This we will take to be 50% of the boiler pressure. If we have a boiler pressure of 130 lbs., our average pressure per square inch, or "mean effective pressure," (MEP) as it is called, will be 50% of 130 lbs., or 65 lbs. This multiplied by the area of the piston will give the total average pressure on the piston in pounds. The area of a circle is equal to its diameter multiplied by itself and the product by .7854.The travel of the piston is equal to twice the stroke, there being two strokes for each revolution, multiplied by the number of revolutions per minute. As the length of the stroke is usually given in inches this product must be divided by 12 to reduce the result to feet per minute.The following example is an engine with cylinder 9" bore and 10" stroke, speed 250 rpm and boiler pressure 130 lbs. This is the size of the J. I. Case engine rated 15 horsepower.2 x 10 x 250 / 12 = 416.6 (travel of piston in feet per minute.)9 x 9 x .7854 = 63.6174 (area of piston in square inches.)63.6174 x 65 = 4135.131 (total pounds pressure on piston.)4135.131 x 416.6 = 1,722,695.5 / 33,000 = 52.2 (indicated horsepower)Taking off 10% for the friction of the engine, .90 x 52.2 = 46.98 or 47 horsepower. This is the power delivered by the engine - brake horsepower as it is called.Courtesy of Science of Successful Threshing. Dingee-MacGregor 4th EditionJ. I. Case Threshing Machine Co., Racine, Wis. 1904
rotorhead1871if steam engines are rated at zero rpm...its all about pressure, and piston area/displacement?
The Alleghanie has a larger firebox and used a better grade of coal in addition. This meant more steam to do more work.
In practice, the Big Boys used their high horsepower. Used mostly on coal, the Alleghainies seldom did.
I have been reading the engine stats on the big boy and the Alleganey and see that the allegany engine is rated at 7500 hp and the big boy is 6300 hp. now the B/B has a bigger piston, bigger stroke and higher steam pressure than the allegany but is rated >1000 hp less.....so what gives???...if steam engines are rated at zero rpm...its all about pressure, and piston area/displacement? correct? ...given the bb has bigger pistons, higher head pressure....bigger stroke......how is the allegany rated at such a higher HP??
Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!
Get the Classic Trains twice-monthly newsletter