4 Replies Latest reply on Apr 26, 2013 8:34 AM by Bill McEachern

    (newbie) Force Needed to Actuate Piston

    Corey Posthumus

      It has been a long while since I used Simulation or had training on it. So after many attempts to get a proper result I have given up and hence my posting this in hopes someone can help me.


      I am trying to calculate the force needed to move the piston down into the device to unseat the o-ring and allow trapped air pressure to be released out the top of the device. I have done a bench test with the actual parts and it is not coresponding with what the simulation is showing. The internal pressure can vary based on the application, but overall the design will stay the same.


      So in laymans, I just want to calculate the force to apply to the top of the piston to slide it back to unseat the o-ring. How do I set this up?


      Results I am getting are completely deforming the piston, or the body.


      Thanks in advance!



        • Re: (newbie) Force Needed to Actuate Piston
          Josh Brady

          The force required will not vary with internal pressure.  You already have the bench test.  What more do you need?

          • Re: (newbie) Force Needed to Actuate Piston
            Jared Conway

            If you apply a prescribed displacement on the piston to move it the distance necessary, if you use result force you will find out how much force was necessary to move it based on resistance from the pressure and friction.


            How are you going to handle the pressure and its change when the opening process happens?

            • Re: (newbie) Force Needed to Actuate Piston
              John Sutherland

              As I see this it is a balanced piston so no force is required to overcome gas pressure when moving the piston, only to overcome friction between O-rings and housing; this will vary with pressure differential across the O-rings.


              I don't think any SW simulation will help you here, even if you know friction coefficients.


              According to what you have modelled I suggest you will have great difficulty reseating the O-ring.


              If your results are deforming piston or body then I agree that it is a long while since you used simulation and I question what you learned then.

              • Re: (newbie) Force Needed to Actuate Piston
                Bill McEachern

                If it was me: I would use a Non-linear 2D static study, put the O-ring in, add contacts as appropriate, use the perscribed displacement as Jared suggested, use a reasonably fine mesh, with friction. If the defromations of the o-ring are quite large you may need the NL properties to define it as a hyper elastic material but you could try it with linear properties and see where it gets you. You may have to set up the o-ring compressed state as the inital step first if you are trying to relax the o-ring and make an opening. I would use a constant step size of about 1/2 an element size or less. You may want to take a look at tutorial or training material before jumkping into this. Good luck as it will be a bit tricky to pull off but can probably be done with Sim Premium..