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Machine for putting repeatable, cyclical loading on steam engine.

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  • Machine for putting repeatable, cyclical loading on steam engine.

    I have recently designed and built a machine which puts a repeating load on a model steam engine. The purpose of this machine was to make the flyball governor work, and to show it controlling the RPM of the engine by opening and closing the air/steam supply valve, as the load on the engine increased and decreased to maintain a constant RPM. I finished the machine this morning, and shot the video. I plan on exhibiting the machine this summer at steam fairs in my area, and part of the project in designing and building the flyball governor was to gain a better understanding myself of how they work.---Brian
    Last edited by brian Rupnow; 12-29-2008, 05:16 PM.
    Brian Rupnow

  • #2
    Thats a pretty interesting way of putting as variable load on the engine.
    I perceived the governor shaft rising at the top of your elevation arm
    showing good control.

    One of the aspects of such an arrangement is control speed at a desired speed.
    Tubal cain had a series ( Model Engineer) back in the 1960's or early 70's when he showed the best speed control. You want the governor at about 45 degrees as yours is, and the arm length determines the RPM for proper control.
    I believe a 2 inch long arm reached the critical range at 160 RPM.
    Shorter arms worked at higher speed to get to the 45 degree angle for maximum sensitivity.

    What is the arm length from the ball center to the pivot point ?
    is the speed range exactly what you want ?

    To explain this to others, if you want to run a steam engine at say 45 RPM and use a 2 inch governor arm, you need to run the governor shaft speed at 3 1/2 times main crank speed ( 160/45= 3 1/2 ~)

    Neat work Brian, and thanks !



    • #3
      On my machine, the length from center of ball to pivot is 1.531". I originally had it set up with 1/2" diameter balls, and it worked very well, but the engine ran at 500 RPM, a bit faster than I wanted. I tried removing a bit of length from the compression spring on the stem post, and although that did slow the engine down some, it made the governor want to oscillate. I changed from 1/2" diameter balls to 5/8" diameter balls, and the engine speed dropped to 375 RPM, with no oscillation. Building this governor was a "trial and error" thing for me, without a lot of applied science up front. I must live right, because it runs very well.---Brian.
      Brian Rupnow


      • #4
        That works very well Brian. It was ball weight,(or size,) that prompted me to ask about musket balls. If you contact a store such as Le Baron, (I am sure they have outlets in Toronto,) you can purchase balls from about 0.32". (SSG",) to about 0.69" or perhaps larger. This would give quite a range of weight.
        Duffy, Gatineau, Quebec


        • #5

          We like to say the governor is "hunting", not oscillating. Weight of the flyballs is important, as is the strength of the spring or spring pack. Will take all your weight to rev up an 800 HP Diesel when it's fired up, pulling on the handle of the governor.

          Quite an effort to do the same on a 10,000 HP steam turbine, also.

          Larger, heftier, the ball, the better control you can achieve. Inertia comes into play. The lighter the flyball weight, the more sensitive to speed fluctuation, oscillation.

          Go larger/heavier, yet, you might get RPM within 10 or so.