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Steam Engine Info. . .HP and RPM???

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  • Steam Engine Info. . .HP and RPM???

    First off, I have never built a steam engine before. . .that being said I have some questions about them:

    1) How do you know or how can you make a steam engine operate at a specific RPM (or RPM range)?

    2) How can you figure out how large to make a steam engine in order to achieve a certain power rating?

    I would like to build a steam engine and use it to actually run a piece of equipment. . .I would like the final speed of 175-400 RPM and would like a minimum of a half HP; I realize that I can achieve the desired RPM by either gear or pulley reduction but if there is a way to design a steam engine so that it operates at the desired RPM right off the bat I would prefer that.

    I know very little of steam engines at the moment and up until now I have had very little interest in them, but I have a project that I think it would be really nice to have a steam engine to run the equipment with.

    Thanks for any and all help!

  • #2
    To maintain a certain speed you need a very sensitive governor, usually a fly ball type that controls the inlet steam.

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    • #3
      Look at existing small engines for ideas.I remember a Shaw engine that was a 2" bore x 3" stroke and was rated at 1/[email protected] steam and 400rpm.

      PM Research sells a kit that's actually a full sized 1/4 hp engine-

      http://www.youtube.com/watch?v=8FXeYKvQQ6o
      I just need one more tool,just one!

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      • #4
        First, Steam Engines are not horsepower rated, Boilers are ....
        The reason is that steam pressure and volume determine the output of the engine itself.
        With external combustion engines , the power comes from outside the cylinders.
        Most designers of steam engines start at the steam source first, and then design the engine, as they know what pressure and volume they wish the engine to run at.

        That being said, your premise is for RPM regulation. A normal steam engine kit will not suffice , as you will have to pay very close attention to the valve design. For ordinary power duties, there is no finer valve gear than a CORLISS valve gear with FULL CUTOFF capability.
        Full ( variable )cutoff is the capability to reduce, or even stop steam flow to the engine at any time during the cycle, based on the governor's position. Fixed cutoff engines, which are quite common, will not give the precise control I believe you are asking for, especially if the load is variable.
        There are variations of cutoff design by multitudes of inventors, and far more than can be discussed here.
        Keep in mind, that electrical generation is probably the most critical RPM controlled demand and if the power generator did not use Turbines, he went with Corliss valve gear
        See:
        http://en.wikipedia.org/wiki/Cutoff_(steam_engine)

        Rich

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        • #5
          Originally posted by atomicjoe23 View Post
          I know very little of steam engines at the moment and up until now I have had very little interest in them, but I have a project that I think it would be really nice to have a steam engine to run the equipment with.
          First, rpm reculation is what you get with most any centrifugally operated governor (such as a flyball governor). If it doesn't cutoff low enough you add mass to rhe balls or lengthen the arms, sometimes you can play with the drive going to it by changing the sheave drive ratio. In the end you're regulating the RPM, power 'regulation' comes with steam pressure.

          Some info on calculation here: http://www.smokstak.com/forum/showthread.php?t=72483 Since you're defining several things (HP, RPM) you'll need to run them backwards to torque then derive the piston face area from the pressure you want to run the boiler at. Typical pressures for a hobby size boiler would be 100-125psi, with expected losses you're looking at a boiler in the 1.5-2.0HP region to get 1/2HP out. In a lot of states that's more area than allowed in a hobby boiler and you're in commercial territory meaning a boatload more regulation.

          Understand that operating a boiler is a labor intensive operation even with a pretty static load. The boiler concentrates minerals in the water so you have water maintenance in addition to boiler blowdowns and periodic cleaning of the mudring. If you're fueling with anything more dirty than propane (oil, etc.) you have to open the smokebox and clean it, if you fire with wood or coal you'll be doing that weekly or more often. You'll be using a bunch of oil (cylinder and lubrication), you can avoid some of that staying away from superheat but it's still there. I would bet that you might average a couple of hours per day overall maintenance.

          There are some really good reasons that electric motors replaced steam.

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          • #6
            Thanks for all the info guys. . .the application is a grain mill (and yes an electric motor would be a LOT easier), but I'm designing our new homebrew system, a 1 barrel (31 gallons) system, right now and I'm drawing a lot of cosmetic inspiration from the steampunk stuff. . .so I thought it would be cool since I will already have propane burners, etc. to run the grain mill off an actual steam engine and flat leather drive belts.

            For a 1 barrel system that's gonna be less than a half hour run time for every 31 gallons of beer. . .it's a lot of work and I'm going to be running an electric motor initialy, but I thought it might be cool to build a steam engine/boiler system as a hobby project to run the mill and have my steampunk looking grain mill actually run off of steam.

            You've got me pointed in the right direction to get started at least. . .Thanks again!

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            • #7
              Originally posted by wierdscience View Post
              Look at existing small engines for ideas.I remember a Shaw engine that was a 2" bore x 3" stroke and was rated at 1/[email protected] steam and 400rpm.

              PM Research sells a kit that's actually a full sized 1/4 hp engine-

              http://www.youtube.com/watch?v=8FXeYKvQQ6o
              Thanks for that link, I'm building the exact same steam engine in my spare time.

              John
              My Web Site

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              • #8
                I seem to recall a figure of 900-odd square inches of heated area per horsepower. That wouldn't be all the factors involved, but would give a rough idea for boiler size.
                Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                ~Practitioner of the Electromechanical Arts~

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                • #9
                  Rich made a good post....in your mind bundle boiler and engine as to what is required with the boiler being the more demanding on so many fronts. Nothing wrong with doing stuff just cause you want to, just go at it eyes wide open regarding the all the expense and hassle of a large boiler. And it won't be cool, it will be rather warm
                  .

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                  • #10
                    Oh, and by the way, you can probably get by if you keep the boiler to yourself, but if you want to show it in public, the state boiler inspectors may want to get involved.
                    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                    ~Practitioner of the Electromechanical Arts~

                    Comment


                    • #11
                      Originally posted by Weston Bye View Post
                      I seem to recall a figure of 900-odd square inches of heated area per horsepower. That wouldn't be all the factors involved, but would give a rough idea for boiler size.
                      That's the number I remember too.I'm building a 1.5hp VFT boiler section for a friend rightnow.19 1" ID tubes x 24" effective area=1430 sq in give or take.
                      I just need one more tool,just one!

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                      • #12
                        You might consider building one of the steam launch engines. I have a couple of the smaller engines from Tiny Power but they have some bigger guys here:

                        http://www.tinypower.com/store.php?c...mode=cat_click

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