Saturday, August 4, 2007

Test of Treadle Pump to Longer Distance and Higher Elevation

With the success of pumping a distance of 160 feet at a height of 25 feet and with an improved strainer, we wanted to try for the maximum distance and height. We ran out of pipe long before we reached the pump’s limitations. The previous 160 feet run was with 1 inch Poly Pipe which was all that we had on hand. So we decided to extend it with standard ¾ inch garden hoses. By using all the hoses I had and borrowing some neighbor’s hoses, we came up with a total of 260 feet. Add to this the 10 feet of suction hose into the pond, we had a total of 270 feet. We also wanted as much height as possible, so we continued to run the pipe up a long hill. At the very end, in order to add more height, we threw a rope over the limb of a tree and hoisted it up an additional 30 feet over the height of the hill itself. To determine the total elevation, I waited until dusk so that my cheap laser level’s red dot could be seen and used it to shine onto lower trees. By making several steps down and measuring the distance from the dot to the base of each tree, then repeating several times, I was able to find the total elevation. The elevation of the end of the run as it was hoisted up to a tree limb was easy to find in that I simply measured the length of rope needed to hoist the pipe all up to the limb. The total was 60 feet from the surface of the pond to the open end of the garden hose in the tree.

We were expecting the pump to be much harder to operate with this increased length and elevation. Instead, it was about the same; just the strokes per minute were slower. It is not necessary to use leg muscles to force the treadles down. Your body weight provides the force. At the end of each stroke, you just have to raise your body weight high enough to step up on the other treadle. To accommodate people of different weights, one can just move their feet position further away from or closer to the pistons to change the mechanical advantage. We measured the volume of water per minute pumped and knowing the total lift, we could calculate the work required. Rate was 4 gallons per minute which is about 50 watts. According to several studies by others, this an easy output for people to maintain almost continuously. Larry operated the pump for 2 hours on a very hot day and was not excessively fatigued. Realizing that we probably weigh more than the average person who will be using this pump, we decided to add several additional inches to the treadle length to accommodate people that weigh less. We feel that except for some minor changes in the way we interconnect the piping so that it is more easily disassembled for cleaning, we have arrived at the final pump design. The following video is about 2 minutes long and shows the pump being tested at the stated pipe length and elevation. There is a short video following the first one that shows Larry operating the pump at this length and elevation after he has been at it for 2 hours. These test results were very encouraging. Our next step will be to get a prototype pump to our CODEP project in Haiti and begin creating drawings and instructions for how copies can be made by others.

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