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Calculations to convert rotational into reciprocating motion in order to get pressure

  1. Sep 22, 2009 #1
    hi there,

    i need some advice please.

    I am a farmer that wants to press some oil seed rape. i have a tractor that produces 80 kw of power at its pto shaft (Power take off) and i want to use this rotational power to produce a reciprocating motion eg back and forth motion. The pto shaft has two speeds approx 500rpm and 1000rpm

    I have attatched a picture to try and show what i am trying to achieve.

    What i would like to know is how i go about calculating the pressure at the piston.

    I have spent many hours trawling the net trying to find the answers and calculations but as yet havent.

    I am using the principle of first class levers.

    I know pressure is force divided by area (approx 4" diameter piston). And force is mass x acceleration. (what mass should i be using? what in this context is acceleration?)

    But how do i get 80kw of rotation to convert to a given pressure in the cylinder.

    as yet i dont know the ideal pressure figure i require to press the oil but i want to try different lever lengths to give me different pressures. and knowing how to calculate it would be ideal.

    Thank you for taking the time to read this and hopefully someone will be able to help


    Attached Files:

  2. jcsd
  3. Sep 22, 2009 #2


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    Re: calculations to convert rotational into reciprocating motion in order to get pres

    This link may be able to help you out:
    http://www.ulb.ac.be/sma/testcenter/Test/solve/basics/work/work.html [Broken]
    Last edited by a moderator: May 4, 2017
  4. Sep 23, 2009 #3
    Re: calculations to convert rotational into reciprocating motion in order to get pres

    thanks minger i am working my way through it.

    Am i right in assuming that the si unit of force is newton metres.

    watts = power
    1 watt = 1 newton meter per second. (force)

    therefore 80 killowats = 80000 newton meter / second (Nm/s)

    80000 Nm/s = 59004.97 ft lbf

    If pressure = F/A F= 59004.97ft lbf A= (4" rad ram) 12.566" sq

    59004.97/ 12.566 = 4695 psi

    So if i forget about the linkage multiplication effect and just use a straight crank type mechanism i should in theory be able to generate 4695psi on a 4" ram. (i am trying to keep it basic to get my head around the topic i realise there is then calculations based on the link minger qutoed)

    Thanks for the help

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