treadle pump findings

the treadle pump team found a lot of things to improve with the current ATC design and some even with the commercially-produced MoneyMaker pump.  they investigated different design concepts for each of their seven categories, and developed three main system approaches to the treadles and overall structure of the device.  ultimately, the students decided to focus their work on the pump body (valves and piston seals).

ATC pump piston with
leather seals

in building the original ATC treadle pump design, the students found a number of areas for possible improvement.  first, they had difficulty creating the pistons and seals, then they had a very difficult time operating the finished project.  it turned out that some modifications had been made by the original team but not captured in the published instructions.  in general, material selection for the cylinders (PVC plastic), pistons (leather), and valves (thin rubber) were not ideal for function, and durability was also a concern.  the ATC pump is high off the ground and could be improved ergonomically, and its weight and size are awkward.  having said that, it was still a great design and a fabulous first shot at the product.  now this team gets to further improve it.

MoneyMaker pump

very extensive benchmarking of the MoneyMaker pump yielded even more information than I expected.  this pump is quite well designed and optimized already.  it’s lightweight, pretty portable, and durable.  the team found that the handle bar fitting was loosely sized, possibly leading to some instability.  they also expressed concern about the durability of some bushings, and were very surprised to find that the cylinders were simply formed sheet metal.  one important discovery was that there is a channel between the two cylinders and an intentional leak path past the pistons.  these features allow water to sit on top of the pistons, both lubricating and sealing them.  the pump is capable of moving 5 gallons of water at a height up to 7.5 meters in less than one minute (with a strong operator).

the team organized their component investigations into seven main concept areas:  piston seals, valves, frames/bases, mobility/stability, treadles, linkages, and intake filters.  they particularly focused on piston seals and valves.

the students explored various seal materials in order to find some that would eliminate the use of leather, improve manufacturability, be readily available, and provide the effectiveness and durability that leather did not.  in addition to the baseline of leather, they looked at hard rubber, rubber from a bike or truck inner tube, and flip flop rubber (which is easily available worldwide).  tradeoffs included availability, durability, coefficient of friction, and formability.  four different seal types were considered:  cup seals, labyrinth seals, u-seals, and flat “O” seals.  each behave quite differently, and, of course, have their own advantages and disadvantages.

rubber patch valve

valves presented another challenge for the team.  they are critical for the pump’s efficiency, preventing backflow of water and keeping air and water flow controlled.  the current ATC design uses thin rubber patches to achieve this purpose, which is inexpensive and readily available, but hampers really effective use of the pump.  the team investigated ball-check valves, hinged valves, shuttle valves, and improvement to the rubber flapper design on the existing pump.  in the end, shuttle valves inside a valve box were deemed the most cost effective and robust.

bike gear concept

three overall concepts were developed for the structure of the treadles and pump body.  the first was a complete plumbing supplies system that would utilize typical materials like angle iron, sheet metal, steel tubing, copper pipe, slip-on pipefittings, and other standard plumbing items.  a pyramidal base platform would be paired with steel tubes for the pump cylinders and copper pipes for the rest of the plumbing.  finally, speed-rail would be used to make the treadles.  the second design concept utilized a bike, something which is readily available in developing countries and can also be found in dumps.  in this concept, nearly all parts of a bike would be useful for building a pump system, including the sprocket and chain as a pivot for the pistons’ up-and-down movement.  wheels would be used for the base, and the handle bars and fork as a handle support for the operator.  the final concept used a t-frame structure similar to the MoneyMaker pump.  additional, less ready-for-prime-time ideas were proposed for possible future consideration, including a flywheel, toggle mechanism, crank mechanism, and recumbent design.

in the end, the students decided to focus on the guts of the machine – pump housing, pistons, seals, and valves.  the outer mechanical structure of the frame and treadles is a possible optimization for another team someday.

next up:  the design solution!



comparison of ATC (rear) and MoneyMaker (front) pumps