Whcih size pulley will produce more power?

Discussion in 'Prony Brake' started by Jerry Christiansen, Jun 27, 2013.

  1. Jerry Christiansen

    Jerry Christiansen Mega Poster WMSTR Lifetime Member

    Hi all,

    The Blue Brake wasn’t at Steam School this year because this is one of the years that the show at the Hawk Museum in Wolford lands on Father’s Day weekend. This year’s trip to Wolford was different than before. We stopped at the Stump Lake Show grounds to do some Prony Brake work.

    A couple months ago I was contacted about bringing the Brake to the Stump Lake show grounds on one of their work days and test a few tractors. The date they had in mind was June 13. That is the day we were planning to drive to Wolford. That was an easy decision to make. Several routes can be taken to get to Wolford and Stump Lake is about 2 miles out of the way on one of the routes. I said ‘yes’ right away.

    A couple weeks later another gentleman from the show called to talk about testing his tractor. He has two sizes of belt pulleys for the tractor and was wondering which one he should use to get more power. During the course of the conversation we decided to try the tractor with both pulleys.

    Owen O and I arrived at the Stump Lake show grounds around 2pm. About 3pm the first tractor was belted up. Later in the day the tractor with the two sizes of pulley showed up. We tested horsepower with the smaller pulley first. The he pulled ahead a few feet, switched pulleys and we tested again.

    Now for the question: Which how did the horsepower values compare? Can you give reasons for your answer?

    The worksheet from the tests isn’t with me now. I will pick it up this weekend and post the results later.

    Jerry Christiansen
  2. Ned

    Ned Mega Poster WMSTR Lifetime Member

    I will stick my neck horsepower is horsepower right? but the rpm's changed and the amount of torque to maintain that horsepower am I close :scratching:

    I vote for both pulleys its got to be a trick question :Shrugs:

    My guess at horsepower is 27hp :sorry2:
  3. Jerry Christiansen

    Jerry Christiansen Mega Poster WMSTR Lifetime Member

    I hate it when I do some editing and then miss a goof like the one in blue above. Originally I was going to ask "Which pulley gave the highest horsepower?" Then I planned to changed the question to "How did the horsepower values compare?". As you can see, the question ending up a bit confused.

    Ned, thanks for the input. The proof is in the numbers that will be coming next week.

    Jerry Christiansen
  4. M Kerkvliet

    M Kerkvliet WMSTR Past President Administrator WMSTR Lifetime Member

    Should be easy... The smaller pulley supplied more power to the brake.

    Cannot be that easy tho. I agree with Ned. Must me a trick in there somewhere.
  5. s.d. jon

    s.d. jon Mega Poster WMSTR Lifetime Member


    I think Ned's educated guess at horse power should be right on, even though color or steering wheel size of tractor is not mentioned.
  6. GKarels

    GKarels Intermediate Poster WMSTR Lifetime Member

    As long as the tractor is not using any additional gearing for one of the pulleys verses the other, the calculated horsepower should be the same (very close). Meaning if both pulleys are on the same shaft, it should be the same. Given all other factors remained the same for each test such as steam pressure, combustion engine temp, steering wheel diameter, steel wheel air pressure, size of the brake block, amount of coffee in Jerry’s cup, ink level in recording pen, etc.

    The smaller pulley will produce more ft-lbs of torque on the brakes scale, but with slower RPM’s. Which I believe are the two variables to calculate horsepower.

    In my opinion.
  7. Ned

    Ned Mega Poster WMSTR Lifetime Member

    Atleast someone can understand the way I do math. Everyone knows that the barometric pressure changes when you deviate from your planned route to go to two shows in one weekend. So if you count the number of yellow stripes on the road divided by the population of the nearest town. Figuring that average air pressure in the steel wheels by the number of coils in the springs in the seat and accounting for wind and oranges are called oranges because they're orange but bananas aren't call yellows :Shrugs:

    It really is just that simple :rof:
  8. M Kerkvliet

    M Kerkvliet WMSTR Past President Administrator WMSTR Lifetime Member

    That's because bananas turned brown to quickly, before anyone could decide to call them yellows. Oranges stay orange a little longer... Long enough so they could come up with a proper name for them.

    The exception would be in Clayton's house. There an orange may turn green before it could be eaten.

    This is all starting to make sense to me now, and that worries me.
  9. Ned

    Ned Mega Poster WMSTR Lifetime Member

    All the restless nights and still no answer :Shrugs: Does that mean I got the answer exactly right? I just knew if I show my work I would get extra credit :rof:
  10. 40avery

    40avery Mega Poster Super Moderator WMSTR Lifetime Member

    Four out of the five voices in my head are telling me that I need to calm down and get to sleep. The fifth voice is asking me if penguins have knees???????:Shrugs:
  11. 40avery

    40avery Mega Poster Super Moderator WMSTR Lifetime Member

    And now I have a sixth one asking if Jerry is ever going to answer his question!!:scratching:
  12. craig mattson

    craig mattson Mega Poster WMSTR Lifetime Member

    Horsepower is torque x speed ÷ 5252.
    The smaller the pulley on the tractor the higher torque but slower speed.

    A good example of how you can change the speed and keep the same horsepower is the red brake on the hill. A steam engine will run approximately 220 to 250 rpm. This is a good speed to run the brake and not smoke the blocks. We also run 540 and 1000 rpm PTO power tests. The brake spins about the same speed due to the gearing in the chain case.. From the 1000 shaft to the 540 shaft is a 2:1 reduction. From the 540 shaft to the main brake shaft, the belt pulley is on this shaft as well, there is another 2:1 reduction. If you have a 10 inch pulley and a 20 inch pulley the 10 inch pulley will spin the brake half the speed of the 20 inch pulley but produce twice the torque.

    For example:

    10" readings - 300rpm 100 ft lbs. This produces 5.7 HP
    20" readings - 600 rpm 50 ft lbs. This also produces 5.7 HP
  13. Jerry Christiansen

    Jerry Christiansen Mega Poster WMSTR Lifetime Member

    Hi all,

    I apologize for being so slow to get the results out. First I forgot the worksheet at Rollag and then our internet connection didn’t work. Finally some answers.

    A simple way to answer the question is to ask another one: (Ned, this is not a trick question.) What are we measuring the horsepower of? The answer is: We are measuring the horsepower of the engine in the tractor. As Gary pointed out, As long as the tractor is not using any additional gearing for one of the pulleys verses the other . . .” . This was a perfect opportunity to demonstrate that fact because the only change was the size of the output pulley on the tractor.

    Often people will debate that a John Deer two cylinder will produce more power on the belt than on the PTO. The PTO has to run through several gears including a bevel gear set that ‘eat up power’. The belt runs right of the end of the crank shaft and loses no power to any gears.

    Another debate is that an IH tractor will get a larger power reading on the PTO than on the belt. The PTO runs on spur gears which ‘eat up some power’, but the belt has to run through a bevel gear set that ‘eats up more power’.

    Let’s get to the numbers. As usual the rpm recorded are the rpm of the Prony Brake and not the rpm of the engine.

    Small Pulley

    Pounds . . . . RPM . . . . Horsepower

    169 . . . . . . . 279 . . . . . .47.2
    183 . . . . . . . 274 . . . . . . 50.1
    187 . . . . . . . 269 . . . . . . 50.3
    192 . . . . . . . 271 . . . . . . 52.0
    195 . . . . . . . 251 . . . . . ..48.9

    Large Pulley

    Pounds . . . . RPM . . . . Horsepower

    163 . . . . . . . 299 . . . . .. . 48.7
    173 . . . . . . . .296 . . . . . . 51.2
    176 . . . . .. . . 293 . . . . . . 51.6
    181 . . . . . . . .287 . . . . . . 51.9
    189 . . . . . . . .273 . . . . . . 51.6

    More data than is shown above was recorded; I only showed the numbers near the peak. The bold print lines are the maximum power for each of the pulleys. The difference between the horsepower values is less than 0.2%. For practical purposes, that means the two values are the same. As predicted by a few people the smaller pulley produced a larger force (and a larger torque 1023Ft-Lb) at a lower speed. The larger pulley produced a smaller force (and a smaller torque 950Ft-Lb) at a higher speed.

    In colculsion (in other words the short answer), the power is the same for either size of pulley.

    Jerry Christiansen

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