Friday, June 1, 2007
The results of the 2" hand operated pump were encouraging enough that the decision was made to build a foot operated treadle pump with two inch cylinders, and an eighteen inch stroke. The long stroke was chosen to enable the pump to move about a quart of water with each foot stroke. This time commercially maunfactured check valves were used. The first photo shows the cylinders with their check valves, and one of the pistons and piston rod. The check valves were installed by boring a hole directly into the side of the PVC cylinder cap, and tapping the hole for a 3/4" pipe fitting. It works just fine.
The frame of the treadle is made of wood. Yes, I know, it's a tall overbuilt monstrosity. It's been made so that it will accomodate cylinders up to four inches in diameter, with strokes of up to eighteen inches. It can also be easily changed to provide different locations for the treadles, pumps and the pulley support mast so we can experiment different configurations that provide different mechanical advantage to the user. That's the reason for all the holes you see in the verticle supports in the third photo. So, think of it as a test fixture that will allow us to determine the best configuration for the finished design, and it won't look so ugly. We had to start somewhere. The good news is that this thing pumps water. Lots of water, to a head of 25 feet, with little effort. We spent the better part of the afternoon pumping water, changing the stroke, and moving up and down the treadles to try to determine the practicle limits of foot stroke length before fatigue and discomfort set in. In other words, a human can only step so high for so long before he gets tired and sore. We're trying to design so as to minimize discomfort and delay the onset of fatigue for as long as possible for the user.
We collected a lot a of data which has to be number- crunched. That's Jim's department. My department is building three inch pump cylinders for the next step in the design. I don't have a video to post this time. There was just too much going on this day. I'll promise one the next time we have the pump up and running with three inch cylinders.