Leather as washer material

[ggggr]

I was thinking earlier on
Is leather only a good piston washer material as a cup washer? I know some gats had a leather washer and I'm pretty sure Ive seen them with a ring of leather in a groove. I've seen older guns with just a plain leather washer as a piston washer.
IF you were that way inclined, could you use leather rings in the Webley Hawks and Ospreys?

Im sure there must be some old guns way back that used strips/ rings of leather as seals?




OK--I'll update this .
CCDJG mentions about a leather cup washer with a supporting disc. Does the leather washer seal because of the "springiness" of the central leather washer? Relums, which dont have great cylinders, used a central washer of fibre I think? Some earlier Gamos (Paratrooper and Sniper?) used a central piece made out of nylon or similar? If you read down here a bit https://www.airgunnation.com/topic/t...istol-variant/ he does away with the inner leather and uses rubber.

Now, I've been tinkering with fitting a leather washer to a Hurricane and Tempest. On one I've done a conventional leather cup washer (first attempt although seeming a good seal, was too tight, sapped power and caused the gun to kick) and the other Ive used a solid piece of leather. HOWEVER, I tightened a stainless steel washer onto this and it has a small lip. Is this still a cup washer? a parachute seal or something else?
Does a leather cup washer need something harder ----and less prone to soaking oil up and distorting, than a leather central washer?

One of the things I was thinking about was how thick does the wall of the cup washer need to be? (obviously with a small diameter cylinder like a Webley pistol, it is very difficult to shape thicker leather). Is a thinner cup and a bigger diameter central washer better or vice versa?

Another thing I thought of, and this was more about did any old gun have it? If for example you had a piston with 25mm diameter and a couple of mm behind the piston head, you turned a groove 5 or 6mm wide and say 2 -3 mm deep, then cut a strip of leather to fit , but cut the ends at a 45degree angle so they would line up. Would such a seal work well-----------or would the air pressure fry to peel if off the piston?
The reason for this idea is that it wold be simple to fit and with the right thickness of leather, , pretty much self sizing.


Just something to think about.

[vintageplinker]

I've only ever seen it as either a cup or just a flat washer with a counter sunk screw
or as you say on gat

Be interesting though, could you try it?

[deejayuu]

Don't see why not Guy. Cord has been used, historically, in similar more hostile applications in some ways.
Leather would be between cord and synthetic "O" ring for me.

[keith66]

I have used plain leather as a piston washer, trouble is finding any thick enough. I was lucky to find an offcut of leather drive belting, it was about 8mm thick.
Webley used to use Phosphor Bronze piston rings in the Osprey & at one time you could buy PTFE Bronze rings for them too.
Another high tech alternative used in high speed pneumatic or hydraulic applications would be PTFE Bronze seals energised by an O ring. Used to be known as Shambam seals.

[vintageplinker]

Yes had same problem finding any thick enough so always return to cup washer

[bill57]

I machine the front off Osprey pistons and thread them to fit a leather cup washer. I stripped and serviced one at the weekend, 710 fps with Superdomes off a nice soft spring (soft enough that I can re-assemble without a spring compressor).

Keith, the piston rings are some kind of PTFE/fibre mix, not Phosphor Bronze. Knibbs and Chambers are selling more modern full PTFE rings for them, I'd be curious to know how well they work.

It's easier to get power from a .22 Osprey, I've had one of them up to 12 ft lbs but .177 is much harder. If you over-spring them they become horrible.

[keith66]

The Osprey i had (a .22) had what i presume was its original rings in it, they were phospor bronze, Replacement ones in bronze filled PTFE i would think were replacements, I had some years ago that i bought from John Knibbs iirc, I sold after i foolishly got rid of the rifle.
One of the most accurate consistent springers i ever had.

[bill57]

I stand corrected Keith.

Nice to hear someone else praising the Osprey, usually it comes in for all sorts of abuse. Personally I think it had great potential - I love the heavy barrel, and find it very odd that Webley dropped that feature on the Viscount. I'm not that enthused by the stock, I find the length of pull too short and the length of reach too long, so I tend to use Tracker stocks instead, which correct both of these shortcomings (for me anyway).

But as you say, when well set up they are capable of surprising accuracy.

[T 20]

The Hawk MK2 and Osprey were fitted with Copper impregnated PTFE piston rings from the factory --- I've never heard of one being fitted with phosphorus bronze piston rings.




All the best Mick

[Lawrie Amatruda]

Yes had same problem finding any thick enough so always return to cup washer

I have in the past superglued two thicknesses of leather together to get the thickness that I required with great success many times.

Cheers, Lawrie

[Peter Dunkley]

Yes they do. I cant see that reversing it would work at all. Why would you want to do this?

[ccdjg]

I have experimented with different types of washer design and materials, mainly with antique and vintage guns, and in general the best was the leather cup washer with an inner supporting disc. The unique feature of this type is that it automatically adapts to any irregularities in the bore of the cylinder. This can be quite dramatic with some of the old wide bore brass cylinders, which are often out of true. A solid leather or synthetic washer, however tight, can leak air like a seive in these, whereas an oiled leather cup washer will give a virtually perfect seal with minimal friction.

[archer24]

Been thinking of swapping round a Premier and a Mk1 piston, maybe now I’ll get around to do it......

[ccdjg]

CCDJG mentions about a leather cup washer with a supporting disc. Does the leather washer seal because of the "springiness" of the central leather washer?

Does a leather cup washer need something harder ----and less prone to soaking oil up and distorting, than a leather central washer?

One of the things I was thinking about was how thick does the wall of the cup washer need to be? (obviously with a small diameter cylinder like a Webley pistol, it is very difficult to shape thicker leather). Is a thinner cup and a bigger diameter central washer better or vice versa?

Another thing I thought of, and this was more about did any old gun have it? If for example you had a piston with 25mm diameter and a couple of mm behind the piston head, you turned a groove 5 or 6mm wide and say 2 -3 mm deep, then cut a strip of leather to fit , but cut the ends at a 45degree angle so they would line up. Would such a seal work well-----------or would the air pressure fry to peel if off the piston?
.

Hi Guy,

These are my thoughts, on your above questions:

1. It is the outer lip of leather that is pushed outwards by the air pressure to give a tight fit against the cylinder wall. The inner washer plays no part in this, and I have used steel, PTFE and leather inner washers with no significant differences. The role of the inner washer is to support the outer lip and prevent it from folding back on itself when hitting the end of the cylinder. So the gap between the lip and the inner washer needs to be small – only a knife blade thickness or less.

2. Flexibility is definitely needed for the cup washer, so that the build-up of air pressure can push its lip against the cylinder wall. This “parachute” effect is especially important when the cylinder bore is irregular.

3. The thickness of the cup washer wall is a compromise - thick enough to a give durability, thin enough to be give the necessary flexibility. I find that 2-3 mm is about right.

4. The type of band leather washer you describe was used with great success in the Hubertus pistol, although the bands were continuous.


I agree that when using leather of reasonable thickness for the cup washer they can be difficult to shape. Because of this, I use home-made steel dies for compressing the wet leather in a vice. After drying, the cup can be removed and trimmed to size.







Cheers,
John

[ggggr]

Hi Guy,

These are my thoughts, on your above questions:

1. It is the outer lip of leather that is pushed outwards by the air pressure to give a tight fit against the cylinder wall. The inner washer plays no part in this, and I have used steel, PTFE and leather inner washers with no significant differences. The role of the inner washer is to support the outer lip and prevent it from folding back on itself when hitting the end of the cylinder. So the gap between the lip and the inner washer needs to be small – only a knife blade thickness or less.

2. Flexibility is definitely needed for the cup washer, so that the build-up of air pressure can push its lip against the cylinder wall. This “parachute” effect is especially important when the cylinder bore is irregular.

3. The thickness of the cup washer wall is a compromise - thick enough to a give durability, thin enough to be give the necessary flexibility. I find that 2-3 mm is about right.

4. The type of band leather washer you describe was used with great success in the Hubertus pistol, although the bands were continuous.


I agree that when using leather of reasonable thickness for the cup washer they can be difficult to shape. Because of this, I use home-made steel dies for compressing the wet leather in a vice. After drying, the cup can be removed and trimmed to size.







Cheers,
John

Thanks John And what about the solid washer with a lip? Is it a cup washer or parachute seal?
The Hurricane is with the deepened piston is shooting really well with the leather cup washer.
Any ideas why most guns with cup washers have leather centres?
I never knew that about the Hubertus