Wednesday, May 9, 2007

Pump Video, Second version

New Seals, New Pump



Since the last video, there has been an improvement in the pump seals. The original piston was machined to squeeze the leather seals against the cylinder walls to make them seal. This worked, but the result was high operating force to move the pump handle. This was improved by making a new piston machined to a close fit to the cylinder wall. The original pistons were turned down to allow the leather seal a much looser fit between the cylinder wall and what are now just seal retainers. Differential pressure between the inside of the seals and the outside of the seals act to force the seals against the cylinder walls to seal in the water, while allowing the seals to flex to accommodate the irregularities in the cylinder walls. The result is a seal that follows the cylinder wall, seals in the water, and requires much less force to move the piston. This afternoon I built a new pump, with the new type seals, check valves installed directly in the bottom of the pump cylinder, and a handle so I could move the pump up and down without tearing my hands up on the piston rod. Then I got my fit young son to operate the pump while I made the video in the next post. As you can see, things are much improved, and we have a good enough pump to use to make some measurements so that calculations can be made to further the design of a treadle pump. Good progress for a day's work.

Monday, May 7, 2007

Experimental Pump Video

Check Valves



We made a pair of check valves from standard PVC plumbing fittings available at a local hardware store. The fitting in my hand is a 3/4" solvent to 1/2" pipe thread reducer. The check ball is a glass marble. The check ball was caged by cross drilling a piece of 3/4 " PVC pipe and installing two pieces of welding rod. In actual practice, a ball bearing would be used in place of the marble, but one the right size wasn't available. This contraption was pressed together, and we had a check valve. The valves were assembled with a tee to our test piston and cylinder, as you can see in the second photo. The next post will show a short video of our made-in-a-day hand pump in operation. The results were encouraging. The voice you hear in the video is my wife who obviously isn't comfortable operating the camera, and is a little confused about the recent goings on in the back yard. Understandably so.

Sunday, May 6, 2007

Cylinders, Pistons and Seals


In the introduction, I said that treadle pumps needed cylinders and valves. They also must have pistons,and seals to keep the water from leaking out around the pistons and the cylinder walls. One of the things we are trying to do is to find a way to make these pumps without having to have a full blown machine shop, using materials available in Haiti. Early on it was decided to try to fabricate as much of the pump from PVC and standard plumbing parts as possible.

What you see is an experiment with using leather washers to make a piston seal. Two washers were used, one to seal against vacuum, the other to seal against pressure. The cylinder is a piece of 2" PVC pipe, with a cap on the end. The cap was drilled and tapped for a ball valve so that I could vary the resistance to flow. Long story short, the seals worked, surprisingly well. The addition of vegetable shortening to the leather improved the seal, and greatly reduced resistance to motion.

The results of the piston seal experiment was encouraging enough that a search for check valves was begun.

Introduction


The purpose of this blog is to document the development of a treadle type irrigation pump. Our efforts to accomplish this are currently funded by the Haiti Fund Inc.

So, you may be asking, what's a treadle pump? It's a foot powered water pump used for irrigation. It usully has two pedals, called treadles, that the pump operator stands on and operates with a walking motion. These treadles are connected to two cylinders with valves at the bottom that comprise a pump. There are two basic types of treadle pumps, lift pumps, and pressure pumps. Lift pumps have a practical limit to the distance they can lift water of seven or maybe eight meters. In Haiti, crops are grown on terraces at greater distances above the water source than that, so a pressure type pump is what's required, and that's what we're trying to design and build.