In praise of the old leather seal

[45flint]

Old type polyurethanes suffer from microbial degradation and basically disintegrate over a long period time. Some polyurethanes suffer from hydrolysis. Fortunately the new polyurethanes have additives to prevent this and will last far longer than the owner of the gun.

Baz

https://polymer-additives.specialche...n-polyurethane

How long have they been available in airguns?

[Benelli B76]

How long have they been available in airguns?

Interesting point. When I started work in polyurethanes in 1994 we were already using additives. There are two types of urethane, polyester and polyether. I think the polyester is more susceptible to bacteria attack. I have Weihrauch seals out of rifles over 20 years old and they are fully functional in good condition. It is difficult to know what material each manufacturer is using without asking for specs. I would think that all manufacturers use modified resistant polymers now.

Baz

[AC99]

Over the years I have acquired a number of Webley mk3's, two of which I had as a lad in the late 1950's. It was then I replaced the leather piston washers on both and they were used for a number of years before being stored and since then have had little use. Both will still hold air in the standard compression test (by cocking, raising loading tap and releasing trigger while holding cocking lever), no air leaking either past the tap or the washer. After almost 60 years both rifles have the same power as they did then.
On the other hand the polyurethane washer I replaced on my Original model 5 pistol four or five years ago has disintegrated AGAIN!
In terms of longevity it seems leather beats polyurethane hands down.

[bill57]

I suspect that the modern synthetic seal is the culmination of manufacturers attempts to move away from leather seals, which they wanted to do to simplify and speed up production. Webley tried piston rings and later the solid PTFE washer, BSA and others tried O-rings, and eventually the modern and almost ubiquitous "parachute" seal evolved.

Leather seals work extremely well, but require softening, sizing and lubricating to work. A synthetic seal, popped out of a mould, goes straight onto the piston and straight into the gun. From a manufacturing aspect it's no contest.

[Dan944]

This is all interesting stuff and I’ve enjoyed reading all these comments.

I converted my Webley mk 3 to a synthetic parachute seal years ago and it really smoothed the shot cycle out and is within 3fps with a certain pellet ,But this thread has made me want to try a leather seal on my 97 just to see how it feels? I currently run orings as just a test and I’m not liking it much, bit too snappy and quick. I like a soft shooting springer even if it is slower than a short stroke which I gave a few for Hft which are short strokes, but my 97 which I bought from New has always been snappy and harsh compared to friends 97s, so I’ve experimented for years trying all sorts, new cylinders, seals ect but I’ve never thought of trying a leather piston seal which would seem quite a crazy thing to do .......but I think when I get a bit of time on my hands I may just try it.

Atb
Daniel