Stroke Force Testing

Objective

Obtain a better understanding of the force needed to operate your water treatment device.

Equipment / Supplies

Your water treatment device, MTS machine, tubing and fittings, beakers.

Method

We will use the MTS machine to repeat the flowrate versus stroke rate experiment you completed as part of physical testing. You will identify relationships between stroke force, stroke rate, work, and flowrate for your treatment device. We will use the MTS machine to measure the force required to depress your water treatment device's piston (or side, for the water bottles) at controlled rates.

  1. If necessary, create a jig to hold your water treatment device in the MTS machine. This may be necessary for the water bottles and water treatment devices with non-flat bases (e.g., Hiker), with cantilevered pumps (e.g., First Need), or transverse pistons (MSR). The MTS machine will "hold" the water treatment device between two horizontal plates, one of which will move a predetermined distance at a predetermined speed (compressing the piston or lever or squeezing the water bottle). If your water treatment device pumps on both the up and down stroke, you will need to attach the piston to the MTS machine.
  2. Identify 6 stroke rates that span the range of stroke (or squeeze) rates identified in the physical testing lab. Use exactly the same stroke rates so you can use the flowrate information from the earlier test. Calculate stroke distance (cm) and time (sec) for each stroke rate. Take into account how your filter works, i.e., does it pump on both stroke directions?
  3. Create a hand-drawn sketch of your treatment device as it will be be placed in the MTS machine, including any jig needed. For water treatment devices with pistons, the figure should include the distance from the bottom of the water treatment device (or jig), as it will be placed in the MTS machine, to (1) the top of the piston at the start of the test and (2) the top of the piston at the end of the test. The piston will start the test fully extended and end the test almost fully closed. Water treatment devices with pistons will be placed in the MTS machine so that the piston is vertical. Any levers will be removed (e.g., Gaurdian, WaterWorks). For water bottle treatment devices, the figure should include the distance from the bottom side of the water treatment device (or jig), as it will be placed in the MTS machine, to (1) the top side at the start of the test and (2) the top side at the end of the test. The top side will start the test uncompressed and end depressed as much as possible. Water bottles will lie on their side.
  4. Use your sketch to determine the parameters needed for the MTS machine.
  5. Run the MTS machine for 6 different stroke (or squeeze) rates. Run each stroke rate 3 times, with the treatment device full of and pumping clean water. Don't get the MTS machine wet! For each run, record in your lab book the stroke time (sec), the stroke distance (cm), the volume of water pumped (ml), and the file name of the MTS data.
  6. Using the data recorded in your lab book and the MTS data:
    • Calculate the flowrate (Liters/min) for each run, based on the volume of water pumped during the stroke (multiply the volume by the number of strokes expected per minute. Using the flowrates for the three runs performed at a given stroke rate, determine the average and standard deviation of the flowrate for each stroke rate. Plot stroke rate on the x-axis and average flowrate and error bars (95% confidence intervals) on the y-axis.
    • Record the number of force data points for each run.
    • Plot each run (distance on x-axis and force on y-axis). Is force constant? Or does it increase or decrease? linearly or non-linearly? Include a representative plot in your final report (and describe it and explain it!).
    • Calculate the area under the force curve for each run, using mathematical techniques such as the Trapezoidal Rule or Simpson's Rule. This is the Work. Calculate the average Power by dividing the Work by the elapsed time of the run. Using the average work and power for the three runs performed at a given stroke rate, determine the average and standard deviation of the work and power for each stroke rate. Make a plot of stroke rate on the x-axis and average work and error bars (95% confidence intervals) on the y-axis. Make another plot of stroke rate on the x-axis and average power and error bars (95% confidence intervals) on the y-axis. repeat the two figures with flowrate on the x-axis. Use your best judgement (explain it!) in deciding to use flowrates estimated from the volumes measured during the MTS test or the flowrates measured during the earlier physical testing. How do your power estimates compare with the results from pressure testing?

If appropriate, discard data from the beginning and/or end of a run in subsequent calculations.

  1. If your water treatment device has a lever, calculate the mechanical advantage. What should water bottle teams do? Plot stroke rate on the X-axis and lever force on the Y-axis. Include error bars (95% confidence intervals) for stroke force.

If your data are unacceptable, you will be expected to repeat experiments outside of normal class time.