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Cable tension question

  1. Nov 13, 2007 #1
    I have a locking device with a cable running through it (think of pieces of PVC pipe with a cable through them). I apply pressure and pull on one end of the cable tightening it and pulling the pieces together so I can lock it with a cam device. To lock it presently it requires 1200 psi (hydraulic pressure) applied to the cable (tension). There is a spacer block .994" long that I pull the cam lock past to get to 1200 psi. I need to increase the locking tension to between 1250 psi and 1400 psi. I need to determine the length of the new spacer. I intend to calculate this as a proportion since the cable, which is steel, I believe should have a constant spring coefficient. My calculation for my next move is as follows:

    I plan to add a spacer that is an additional .085" in length making the overall spacer length 1.079"

    .994"/1200 psi = 1.079"/X psi

    X = 1.079"(1200 psi/.994")

    X= 1302.615 psi

    Does this make sense?
  2. jcsd
  3. Nov 13, 2007 #2


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    Science Advisor

    Assuming that everything is linear this makes sense. If we were talking about a rigid bar then since it is a low stress, you should definitely be in the linear range. I think you should end up close enough to what you want.
  4. Nov 14, 2007 #3


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    Gold Member

    The stress is negligible compared to the yield strength of steel. A linear approximation is appropriate.
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