Wednesday, May 9, 2007
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.