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Float Calculation

Abstract

In the fall semester of 2009, Non-linear Chemical Doser team developed a Mathcad file to help operators determine the float parameters given a non-linear doser lever arm. For our prototype, we calculated that our float needs to weigh 4.95 lbs with a diameter of 6 inches and 4 inches of thickness.

Method

The float design parameters can be determined using a moment balance around the pivot of the lever arm. (Can you detail this moment balance? A diagram perhaps and the equations and the result of these equations.) This is to ensure that a change in head in the entrance tank will cause a similar change in the relative height of the float. (Can you make the previous sentence a little clearer? What ensures a change in head in the entrance tank will cause a similar change in the relative height of the float?) We first determined the weight and location of each components of the lever arm with respect to the pivot. (How? You don't show or give a method here.) We then identified all the moments for each of those components. (What were all of the components?) We then specified a float diameter and specified and solved for the weight of the float with the specification that at equilibrium the float will be halfway submerged in the water. (Okay...isn't this inherent in what we assume with bouyancy? Where are you using bouyancy principles in these calculations?)

Results/Discussion
The scale portion of the lever where the dual scale and the slider and the doser tube are connected is heavy enough that there will always be tension on the float. As water level in the entrance tank rises, the buoyant force of water will push up the float pushing up one side of the lever arm will increase until the lever arm (on the other side of the pivot) on the scale drops releasing the necessary alum flow rate while maintaining the tension on the float. (Maintaining tension is a very important point. Can you show the calculations that illustrate your point?)

Conclusion and Future Work

We require a float with a weight of 4.95 lbs, diameter of 6 inches and 4 inches of thickness (maybe I missed it, but where did you come up with 4 inches of thickness?) for our prototype lever arm.

Once we build the lever arm, we would further specify the float parameters by utilizing a makeshift float that we can adjust prior to ordering the final float for the design competition. (Sounds like a good plan to me.)

Bibliography

Deliverables

  • Final Float Design Parameters and Calculations
  • Float protype for March 2010 EPA Competition
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