Sunday, July 8, 2007

Paraffin Molded Seals

Early on in this project, while we were studying treadle pumps in general, and leather seals in particular, we ran across several references to making seals by soaking leather in melted paraffin(candle wax) and pressing the still hot leather into a mold. In an earlier post I wrote about making molded seals using the pump pistons and a section of PVC pipe after soaking the leather in warm water. Since then we've made molds for making paraffin seals, which you can see in the first photo.

The base and and piston are made out of old countertop material. They could be made out of anything, even wood. The rings are short sections of the same four inch PVC pipe that's being used for the pump pistons. There's a large 45 degree bevel at the top of the rings to help ease the leather into the mold without tearing it up. Today, I finally got around to molding seals. Five inch diameter leather circles were soaked in melted paraffin, and placed in the molds. The bolt through the center of the mold was used to tighten down on the leather and force it into the mold. It worked like a charm. The only problem was that I made the rings a little too short. I improvised by taping the rings together with masking tape, and using one mold at a time. I'll make taller rings later. The second photo shows one of the seals out of the mold, and one of the seals still wrapped around the piston, waiting to be trimmed. I trimmed the edges of the seals with the razor knife to the left, using the top of the piston as a guide. I have no idea how well these will work. We've read that these seals will be self lubricating, and less prone to rot and swell from absorbing water. We'll try these seals the next time we take the pump out for a walk, along with the new check valves we made today. That's what the next post is about.


Graham Moore said...


I am quite interested in your leather bucket seal manufacture. I am designing a hand pump for Papua New Guinea that I would like to be completely made with locally available components and materials and a minimum of tools. (Apart from machettes, tools are in short supply in the village!)

I have every thing worked out for the pump using standard PVC fittings and some inner tube rubber for check valves, but am still struggling with bucket seals for the piston. I can buy them in Australia, but am trying to avoid that if a I can find a way of simply fabricating them.

Your seal looks good. Have you any experience on the seals in service?

A seal that I have purchased is relatively hard and stiff. Is that because it started off as soft leather and is stiffened by the solidified candle wax in the leather?

Smitty said...

As it turned out, the paraffin molded seals didn't work as well as we had hoped, either. Since that time, we have published a webpage about leather seals and pistons at More information is available there.