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Building the Trevithick Engine

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  • Sparky--I know that the world is full of incredibly innovative and useful stuff. However, when I need something I need it right now. Not 3 day shipping, not delivery by drone, not something coming overnight from Toronto. I need to be able to jump in my truck, drive somewhere in Barrie, and be back home using it before the next daily mealtime. This does not always work in my favour, but I'm an old guy and might die before something gets here, even with overnight shipping. This probably works for me about 85% of the time.--And I had the pressure cranked up to about 70 psi when the line blew off inside the boiler shell.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • Originally posted by brian Rupnow View Post
      Sparky--I know that the world is full of incredibly innovative and useful stuff. However, when I need something I need it right now. Not 3 day shipping, not delivery by drone, not something coming overnight from Toronto. I need to be able to jump in my truck, drive somewhere in Barrie, and be back home using it before the next daily mealtime. This does not always work in my favour, but I'm an old guy and might die before something gets here, even with overnight shipping. This probably works for me about 85% of the time.--And I had the pressure cranked up to about 70 psi when the line blew off inside the boiler shell.
      There ARE hobby shops in Barrie ! I'm a old guy too, but every once and a while I still learn new tricks.

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      • Sparky--I know there is a hobby shop in Barrie. I go there every time I'm out and about looking for parts. I go to Ideal Hobbies, Busybee Tools, Princess Auto, Canadian Tire, and to Brafasco (nuts and bolts). I go to Majac machine tools for taps and milling cutters. I go to A to Z Metal Supply for raw steel or aluminum. Some of the stuff I need is simply not available in Barrie, and I do buy it online and have it shipped to me. Mostly though, when I am in the "Heat of the moment" I don't like to wait 3 to 5 days for whatever I need.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

        Comment


        • After a full day of fixing disconnected tubing and taking things apart and then putting the parts all back together again, it was time for some analysis as to what was happening. Right now, as things set, the valve is set so that it is fully opened at the end of the piston stroke in either direction. Now, in a perfect world, where the flywheel really was doing it's job, the inertia of the flywheel should carry the crankshaft "over the top" before the piston begins to travel in the opposite direction. Since the flywheel is bouncing back and forth between the top and bottom dead center, the conclusion is that the valve is being actuated just a tiny bit too soon. If the opening was delayed for another millisecond, the crankshaft would have that space of time to get "over the hump" and make complete revolutions rather than bouncing back and forth thru partial rotations. So yes Charles, I do agree with what you are saying and what you show in your diagram. With everything "as designed", I can adjust the sliders so that the valves begin to open a bit later in the cycle, which in theory mean they would close a bit later in the cycle. That would be a "best case" scenario. If that doesn't work, then as Charles suggested, shortening the radius arm on the valve would allow the valves to operate closer to the end of the piston stroke and hopefully allow the flywheel to get "over the hump" before travelling back in the opposite direction. I have the capacity with my current design to shorten up the radius arm with no other changes.
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

          Comment


          • Bah!! Humbug!!--The easy fix (repositioning the valve actuators) didn't work. I have never had an engine so close to running that didn't actually take off and run. I can see a number of things which I could do to fix this, but they are all progressively more and more difficult. The next easiest fix is to shorten the radius arm on the valve. Of course this will make for an extended cantilever on the sliding brass actuator. I have a small (3mm) ball bearing that I think I can work into the equation to take a bit more friction out of the valve action. Oh well, thanks to Covid there is damn all else to do anyways.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • Perhaps adding temporary weights to the flywheel might allow it to get "over the hump."
              Allan Ostling

              Phoenix, Arizona

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              • No, yesterday I did make a much heavier plain plate flywheel, and although it helps it's not quite there yet. This morning I frigged around with different settings on the actuators, but it didn't help. Right now I'm making changes to the length of the lever arm on top of the valve.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

                Comment


                • https://www.youtube.com/watch?v=Wco5RXN3cXc
                  This is my Trevithick engine doing something I haven't seen before. It has a unique 4 way valve mounted on top of the boiler, and the valve swings back and forth under the influence of the sliders which contact the valve arm. I don't have things set up quite right yet, so the engine is "stuttering"---The valve is being reversed before the piston gets far enough in it's linear travel to get the crankshaft over dead center and complete a full revolution. This is not what I am ultimately aiming for, but I hope that with some adjustment to the sliders I can coax it into full revolutions.---Brian
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

                  Comment


                  • You have the beginnings of a nice water pump there!
                    it seems that your timing of the 4 way valve is terribly off. It actually needs some dwell time in the off position in both ends of the throw, to allow the inertia of the flywheel to do its work.

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                    • If its still real tight like before and you have to run high air pressure , that would counteract the effect of the flywheel to a large degree. Have you gotten things to free up? I would expect that to run on quite low air pressure if things are not binding up, 20psi or so.

                      Its a easy calc to take the piston diameter and the air pressure to figure the force a cylinder is producing. I bet its a lot more than you would think to overcome the binding.

                      What is the cylinder piston diameter?
                      Last edited by Sparky_NY; 10-18-2020, 02:22 PM.

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                      • I've tried all of the tricks in the "Rupnow Magic Hat" and I am not able to get this thing to run using the 4 way valve. It is one of those engines that wants to run so badly that you can almost taste it, but it isn't happening. I have tried all of the different settings that I can think of, and have pinched my fingers so badly that I cried like a baby, but this just isn't going to run for me. This is not to say that the project is abandoned--Just that it isn't going to run with this 4 way valve. I can salvage most of the parts and make a Trevithick engine that runs with a more conventional slide valve. I hate to admit that I haven't been able to get this to work, but I have tried everything I can think of. Weirdly enough, I can make the model look more like the original Trevithick by using a conventional slide-valve than I could of if the 4 way valve had done the job.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

                        Comment


                        • Sparky--It has a 3/4" diameter piston. At 60 psi the piston generates 26.5 pounds of linear force.
                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

                          Comment


                          • Best wishes for the slide valve! Am I right in thinking that others have tried and failed to get the 4-way valve to work?
                            John

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                            • John--I don't really know. In all of the research I have done on this engine, I have only seen two successful models, one made in Atlanta Georgia one made in Germany. The 4 way valve does work. I have posted a video of the one I made working somewhere in this thread. The problem isn't so much with the valve itself, but the timing events. There is a definite time envelope between when the valve shifts and the crankshaft goes "over the dead spot" to continue the full 360 degree rotation. If the valve shifts too soon, then the engine oscillates but doesn't rotate. If the valve shifts too late the piston just freezes in position. There is also a direct relationship between how soon the valve begins to open and how far the valve opens.---Brian
                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

                              Comment


                              • It seems to me that the 4-way valve isn't changing just a little early, it's changing very early. Clearly changing early enough that the pressure/piston actually stops the engine (despite the large flywheel) and reverses it before the crank turns over.

                                The rod that actuates the 4-way valve - I'm assuming the stops are there to adjust when the valve changes, and I guess I'm also assuming they can be adjusted. If you can move these along the rod, can you back them off entirely so the engine stops with the piston in the top/bottom positions? If so, I believe at these points you want the valve midway between positions, not transmitting pressure, and only beginning to open as crank turns over and the piston begins to move in the other direction.

                                EDIT - Going back and stopping the last video several times, it appears the stops on the smooth valve actuating rod are held in place with set screws(?), giving you a coarse adjustment of the valve timing. Hopefully that amount of adjustment is enough. If not, would it make sense to put a screw in those stops, parallel to the valve actuating rod, to give you more fine adjustment of the valve timing?
                                Last edited by DrMike; 10-19-2020, 07:37 AM.

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