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Dynamic Stroke Length

  1. Sep 24, 2008 #1
    Hey guys,

    I'm trying to design a reciprocating pump engine with a dynamic stroke length.

    basically something like this: http://www.animatedsoftware.com/pics/pumps/animpist.gif

    However I wish the stroke length to be variable and dynamic. The only way I have found so far is the change the r value from the origin of the wheel to the connecting rod. The issue I'm running into is one of balance. If I use a linear actuator or some such to change the r value the wheel will not be balanced and cause vibration.

    anyone else got any ideas?
  2. jcsd
  3. Sep 24, 2008 #2


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    Hi Setix. Couple thoughts...
    - Why change stroke length? The only significant change to the process is to change flow rate. Note here I'm assuming by "pump" you mean liquid displacement, not gas, which would be "compression". Since the only alteration is flow rate, you could just as easily alter RPM using a VFD. Granted, sometimes a VFD isn't practical due to other issues, but generally a VFD is the most economical and practical solution to variable flow recip pumps.
    - The second question is simply, why are you concerned with balance/vibration. I design recip pumps for a living that go to 10,000 psi and at rates up to ~ 50 GPM for a single cylinder. There are 2 primary balancing considerations in such pumps, the rotational one (primary) and the reciprocating load (secondary). If you devise a method of adjusting stroke length, I have to believe it's something you could adapt to also adjust your rotational counterweights. That said, most of these 'smaller' reciprocating pumps such as I design, hardly need any balancing because the dynamic load is fairly small. If you're off a bit on the balance, no big deal. Note this is common for the industry.
    - If the intent of varying stroke length is critical to the design, have you done a patent search? There are a number of patents on this type of design already and if you're seriously designing something like this, you need to be aware of what's being done in the field.
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