Pistons and Leather Cup Seals
Information on this page is about making and fitting pistons and leather pump seals. The links provided here will take you to Treadle Pump Blog Posts with additional information.
This page is new and under construction. Readers are warned that the plans linked by this page and the information on this page are preliminary and subject to change without notice. So, until we've got a better handle on what we're doing, feel free to visit and look around. We'll remove this notice when the information here has firmed up to the point that it's considered dependable.
 
 

Each pistons assembly requires three PVC discs. These discs can be made from a section of four inch PVC pipe. Cut a four and a half inch piece of pipe, slit it down one side, and heat it in an oven set at its' lowest setting, about 300-325 degrees. The plastic will become very pliable in a very short time. Don't walk away from the oven. Wearing gloves or oven mitts, flatten the hot section and place it between two flat surfaces to cool. Once cool it will remain flat. I used kitchen cutting boards to hold the plastic flat while it cooled. Scraps of plywood will work too.

 

This flattened plastic can be cut into discs for pistons and seal retainers using a jig saw, band saw, or coping saw. Any woodworking type saw that will cut a curve will do. You will need three discs of plastic for each set of piston/seal retainers.

 

You will need two sizes for each piston, two smaller and one larger. The larger size needs to be cut to fit the inside of your cylinders as closely as possible without binding. Once cut, if you need to adjust the size a little, it can be done with a wood rasp. This larger circle will be the center disc. Drill a 3/8 inch hole in the center of your center discs and seal retainer discs. Install each piston disc on a piece of 3/8” all thread rod, with a nut and flat washer on each side. Check for fit by running each piston disc through the cylinders. They should fit closely without binding.

 

 

This seems like a good time for a photograph. You can click on the photos to enlarge them for better viewing.

 

The cup seal retainer discs will have to be sized depending on what leather you are using, as different leather differs in thickness. These discs, hold the leather against the cylinder walls. Sizing them appropriately will require some trial and error. Make the leather cup seals by cutting five inch discs out of your leather. Make a 3/8" hole in the center. The leather we used was purchased from Tandy leather. It's the type used for tooling, vegetable tanned. Soak the leather discs for about fifteen minutes in warm water, and install them on the piston rods, sandwiched between the center discs and seal retainer discs as shown in the photo above. The leather should be very pliable when wet. With the seals installed, the piston Assemblies should move in the cylinders with only the slightest resistance. If not, it will be necessary to reduce the diameter of the seal retainers. Again, a wood rasp will do this nicely. Once you’re satisfied with the fit, press the edges of the seals flat against the cylinder walls, and let them dry completely. Once dried, they will hold their shape, even when wet again. The photo below shows wet seals drying in short sections of pipe of the same type and size used to make cylinders.

In the photo the seal retainers are made out of clear plastic. In actual practice, PVC would be used.

 Also, the seals here are installed on finished piston rods comprised of a piece of all thread rod, a coupler nut, two locking nuts, and an eyebolt.