(I apologize for reviving this old thread. I'd like to document this here in case someone needs to replace the leather washer/cup as I did.)
I stumbled upon a MDI pump in good shape. The leather washer/cup still works but will need to be replaced soon. I was successful in using the following procedure to make a new one. Total time was less than an hour:
- Material: 2-3 mm thick leather. I used an old straight razor strop. I believe an old belt or shoe may also work
- Cut the leather into a round disk; 8mm wider than the piston inner diameter. Use scissors to cut the disk and a box cutter or razor to cut the center hole
- Soak the leather disk in hot water (from tap, not boiling) for 5-10 min
- Disassemble the pump. Remove the original leather cup
- Using hands, fingers, and whatever tools you may have on hand, shape the leather disk into a cup. This may take about 10 min. Re-soak the leather if necessary. The rough side of leather is the cupped side (down when installed)
- Install the new cup on the pump rod with the original two metal washers and nut
- At this point, the new cup's diameter will be about 3mm too large. Use a hose clamp to form/compress the leather cup to the correct size
- Remove the hose clamp. Coat the leather cup with grease (I used white lithium grease)
- Assemble the pump. Pump may not work initially. Wait a few hours for the leather cup expand to its final shape forming a proper seal. Also apply more grease if needed