How to make a leather piston seal (2007) | Hacker News Reader

How to make a leather piston seal (2007)

pyramydair.com

42 pointsbrudgers13 comments

Sometimes old tech is best tech! Thanks for this. Although, my experience suggests that using a drill bit to put holes in leather is not the way. What you want to do is punch the holes. Easy to do...find a short length of steel tube of the right diameter and grind a sharp edge on the circumference. Or, you can buy any number of punches cheap.

Most casual, but certainly all hard-core cyclists will know the legend of the Silca frame pumps. Silca has been using leather washers forever. Read more (why leather works and why o-rings don't) here: https://blog.silca.cc/uniquely-silca-the-leather-washer

A leather hole punch is a handy tool. It's great for making holes of assorted sizes in almost any thin material. I use it for adding clean holes to my belts when they stretch out.

Thanks for the link! MSR uses leather pump cup seals in their liquid fuel stoves, and it's nice to get some background on why this is the best choice from an engineering perspective.

I'd intuited some of the points in the article, but it's good to know that somebody has approached the subject rigorously, and taken the time to explain why leather is superior in this application.

In a fuel pump, the washer also has contact with substances that are aggressive to rubber: the stove fuel itself. I doubt a rubber o-ring would survive long in that environment.

There are fuel resistant rubbers available, most commonly Viton/FKM. They are commonly used in automotive applications.

https://en.wikipedia.org/wiki/FKM

The pump cup, in theory, never touches fuel. And goodness knows MSR isn't shy about using O-rings. There are nearly half a dozen in a Dragonfly between the pump and the stove. They're using a material that holds up to fuel contact for those.

Most of this seems to be the advantage of cup-washers versus O-rings. Wouldn't that be possible with rubber also?

Thanks for this article. It reminded me of the times I fixed my old air rifle as a kid by doing nearly exactly what he described.

My kid method was to use the original seal as a pattern (Mom did a lot of sewing so I totally understood how to fit things and allow for seams, etc). I would use a leather hole punch to punch the hole for the screw and just re-use the screw. Then with a pattern made, I'd oil the seal with neetsfoot oil, sno-seal, or whatever I had handy for softening the leather. You could also just use water but it will dry out eventually. If that's what you got today, that's what you use. It just meant that I would have to disassemble the thing again to wet the seal.

Once the seal is wet and screwed to the plunger you just shove it into the chamber and reassemble things. It doesn't take long.

Leather punches can be purchased for a few dollars from Tandy Leather. There are many styles to choose from. The multi-punch wheel style is super useful around the house for punching holes in just about anything. For many of you, the time you spend sitting while you work will eventually cause you to need an extra hole in your belt. Be prepared! You'll eventually need a new belt though so here is a link to Tandy.

[Tandy Leather Hole Punches](https://tandyleather.com/collections/tools/punches-&-setters)

Another thing I discovered over the years is that leather seals were also common on hydraulics. I had an old Farmall Cub tractor with a hydraulic pump that began to leak furiously. After I tore it down I found a worn leather seal and a couple of rubber washers that were bad. I just made a new seal and a set of washers from old leather that I had bought 30 years before to do saddle and tack repair back when I had a horse. It all worked great with no leaks when I reassembled the pump and mounted it back on the tractor.

The important thing is to match the thickness and shape of the original seal as closely as possible. Then lube the seal so it forms an air or fluid tight seal and you're good to go.

Leather punches are also great for bolt holes in gaskets.

Yes!

This is another thing that I have used mine to produce. I forgot about that.

I keep gasket materials on hand for this and use a small ball-peen hammer to tap out the main gasket and a punch to pop the holes. You may have to make a minor touch-up with an exacto knife but usually the gasket works great.

I bet I can use that to fix the seal in a bicycle pump that I cannot get a replacement seal for. Thanks for sharing!

Just wonderful, would never have thought to do this

This is a great knowlecule.

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