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Off topic - any CNC experts, or plasma cutting gurus?

  1. Feb 1, 2010 #1
    Hi guys.

    I need some ideas on making something similar to one of these:

    http://www.pumpschool.com/images/Cutaway-Classic+.jpg [Broken]

    Only the one I'm trying to make will pump 200+PSI, and be driven from red hot exhaust.
    Swept volume is going to be around 4 liters per revolution.

    I looked into buying one from the boys in china, but they're about 10k for that size, and not even equipped with cooling passages in them, which I obviously need to run it from exhaust gases.

    My idea I had was to create a 2D end aspect of the lobe rotor, and then use a plasma cutter to create many many pieces that would later be held together by long nasty bolts.

    Does anyone know how accurate a plasma cutter is for this type of thing?

    I'm thinking if this needs to be CNC'd from solid steel stock, It would probably cost 20k for the first one, and at least 5k each for more......

    I could find roots blowers from old detroit diesel engines, but those were never designed for the pressure I plan to inflict.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 1, 2010 #2


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    Sounds like an interesting project...um...forgive my ignorance, but what is it :blushing:?
  4. Feb 1, 2010 #3
    Hand held plasma cutters will never get the detail you need. Most CNC machines you will find available for your use, most likely wont do something to that extent, and are used for cutting plate steel.

    A lathe would work, but that requires a lot of man hours which means big bucks. Your best bet is to suck it up and actually buy a real one, because if something goes wrong you at least have a warranty to fall back on.

    It looks like some sort of rotary positive-displacement pump. That is my guess anyways.
  5. Feb 1, 2010 #4
    It is going to be a type of rotary engine. :confused:

    I'm not trying to take over the automotive industry, but this engine is supposed to run better than a normal piston engine for the specific purpose that we need it for.

    It will run on diesel-ish fuels.
  6. Feb 1, 2010 #5
    You do realize that rotary engines never work well, at least my experience with them. This kind may be different.

    How big is it going to be? As you said it is an engine, how will it run off of its own heat? Will it be running off another vehicles heat?
  7. Feb 1, 2010 #6
    I know a guy with a nice lathe, but said that would never come out right.

    Buying one with warranty is not an option, as I'd be providing them the design, in turn handed a "have fun and call someone else if it doesn't work" product.
  8. Feb 1, 2010 #7
    It is supposed to be.

    The difference between a rotary engine and this, is that we are not attempting to create a combustion chamber in the pump, unlike traditional rotary engines, and piston engines.

    This will create rotary motion from the exhaust gasses coming from the reactor muhahahaha. LOL.
  9. Feb 1, 2010 #8
    Ahhh ok ok I got you know. You are taking a hot gas or liquid and making it turn this tri-lobe rotary engine to power something?
  10. Feb 1, 2010 #9
    Hot Gas.....

    There will be a second unit pressurising the combustion chamber, with raw gasses from an oilwell.

    The hot exhaust drive pump will spin the slightly smaller compression pump.

    Both pumps will see huge pressures, and the one will get some serious heat.

    Unlike a piston engine, this will be able to burn raw natural sour gas, and not get weird deposits in a crank case, or acidic residue on piston rings etc destroying it.

    The thing will obviously still rot eventually, just not nearly as fast as you're average motor.

    Power generated from it is not expected to be breath taking, but this could make more sense than just flaring the gas to a stack and burning it to get rid of it.
  11. Feb 1, 2010 #10
    Hmm. Do you mind me asking what the application is that you are using this for?
  12. Feb 1, 2010 #11
    Generating power from garbage gas found at multiple oilwell production sites, and possibly landfill gas too.
  13. Feb 1, 2010 #12
    So you are going to generate power from the gases coming out with the crude? I know that they pump in Co2 to make the well pump faster, so would you be using this gas to power your machine?

    Sorry if I am not understanding, I dont work on a rig!
  14. Feb 1, 2010 #13
    just based on when i read about these for automobiles, i don't think i ever saw a supercharger driven by anything other than a belt. i assume there may be some practical reasons for this. turbos have a problem with lag where they don't spool up right away, and maybe that's OK if it's not positive displacement. how are you going to run your engine (i assume that's what you're doing) if no air can get to the engine because your exhaust isn't turning the pump yet?
  15. Feb 1, 2010 #14
    It doesn't sound like a turbo or a super charger, but something for oil well production. I could be wrong though.
  16. Feb 1, 2010 #15
    OK, if you understand how they work for a car,

    I'm trying to take 2 of them, and burn gas in between them, and because one is smaller, they would start rotating, thus forcing in new fresh air to continue burning.

    They will theoretically work exactly as a jet engine, only with positive displacement pumps rather than the normal fan compressors.

    I had thought about making a small set to try in place of the turbocharger on my truck, but thats a whole other story LOL.
  17. Feb 1, 2010 #16
    yeah, well, i get the concept, but i was trained as a EE, not a ME, so probably not the best person to ask about thermodynamics. you might want to try the engineering forum, there do seem to be a lot of sharp people there. i just have a sort of gut feeling that it might be overly complicated to make it work correctly (maybe you'd need a bypass to start the thing). even with two exhaust turbos tuned to rotate the pumps at low and high exhaust velocity, i just get the feeling it might choke. but who knows, for a non-automotive application, it might not matter to get things like smooth acceleration.
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