Thursday, June 21, 2007

More About Leather Seals

Until now, we've been using leather that was on hand, left over from other projects, to make our pump seals. About a week ago I went to a local Tandy leather store. I explained to the gentleman running the store what I was trying to accomplish, and he showed me the type of leather that he felt would better serve to make seals. This post is about our first attempt at making seals using the new leather. I've also received a comment, which was really a question, about how we make our seals. I'm going to try here to illustrate what we're doing and how the pistons, seals and seal retainers go together.


To make the seals I first marked five inch circles on the leather using an ordinary compass. The circles were cut out with a sharp knife, and a 3/8 inch hole cut in the center. The leather circles were then soaked in warm water for about half an hour. I used the pump pistons and seal retainers to hold the seals, and forced them into two short sections of four inch PVC pipe of the type we're using for the cylinders. The first photo shows the seals in the molds. The edges of earlier seals were convoluted, or accordian shaped. This leather is much more pliable than what we've been using, and I was able to smooth out the humps and bumps using my fingers.

In the background of the second photo (click on the photos to enlarge them for better viewing) you can see a piece of the leather that I used, and the short sections of PVC that were used for molds. In the foreground are two of the now cup shaped seals , dried and with their edges trimmed, more or less. In the middle are the two pistons. One has the new seals installed, and the other is positioned to show as best I can the piston and seal retainers. The piston is machined to a close fit to the cylinder. The retainers are quite a bit smaller than the piston, with generously radiused edges. Their purpose is to loosely hold the leather seals without forcing them against the walls of the cylinder. Pressure or vacuum in the cylinders formed as the pump operates forces the seals against the cylinder walls. If all goes well, tomorrow we'll try another version of the pump, with these very seals.

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