Original Diana 35 - elastomer piston seal ? Better?

[Hsing-ee]

PTFE has a small band of devoted devotees. It is interesting to note that manufacturers have produced airguns with the following sealing materials:

Leather
'O' rings
Polyurethane parachute washers
Steel piston rings

None of them have used PTFE. It was experimented with by the tuning houses of the late 1970s and early 1980s and discarded. Various individuals have used it and some say it works great, but its ability to deform and its lack of ability in terms of sealing well when anything isn't 100% round means it will never be a popular choice.

T.R.Robb sells PTFE washers to the true believers and that's probably where it begins and ends in 2017.

I used it once and it was shit.

[Hsing-ee]

Last of the Welsh PTFE maniacs? Everyone knows Dianas run best on leather (German- leder). At least mine do so do as I say, pal.
Away and fashion a pair of PTFE socks or that if you want to do something useful with it... Second thoughts: don't bother- you're feet are out of round .

Probably because the transfer port is large, to allow for the sedate leather-braked piston speed...

[jonnyone]

PTFE has a small band of devoted devotees. It is interesting to note that manufacturers have produced airguns with the following sealing materials:

Leather
'O' rings
Polyurethane parachute washers
Steel piston rings

None of them have used PTFE. It was experimented with by the tuning houses of the late 1970s and early 1980s and discarded. Various individuals have used it and some say it works great, but its ability to deform and its lack of ability in terms of sealing well when anything isn't 100% round means it will never be a popular choice.

T.R.Robb sells PTFE washers to the true believers and that's probably where it begins and ends in 2017.

I used it once and it was shit.

Webley used it on Vulcan and others. A friend of mine bought one for his 77 and it was as you describe above. The guns I have ptfe in have simple flat washers that replaced leather cup washers. Maybe that could be the difference. That and the cylinders are true (possibly).
Out of interest what gun did you try ptfe in?
Dave

[Drew451]

Aye, the Vulcan had PTFE in conjunction with a buffer washer. I had one. Seemed to work well enough.
If your PTFE'd Diana's have been working well for you since 1986 and the seals have not been hammered out of shape and worrying the cylinders then I can respect your point of view on the subject. It's not as if your trying to convert the masses.
I will stick with original (pardon the pun again) leather, myself. Works very well for me.

[jonnyone]

Aye, the Vulcan had PTFE in conjunction with a buffer washer. I had one. Seemed to work well enough.
If your PTFE'd Diana's have been working well for you since 1986 and the seals have not been hammered out of shape and worrying the cylinders then I can respect your point of view on the subject. It's not as if your trying to convert the masses.
I will stick with original (pardon the pun again) leather, myself. Works very well for me.

They seem to work well enough Drew.
The local squirrels are not fussed on them though.
Deffo not trying to convert the masses mate. Just giving honest feedback of my experiences, good, bad, or indifferent.
Certainly want to try the now available converters to go the OEM route or even another material that performs equal or better from here on though. I'm sure that some of these old classics can be improved by them but obviously with springers you can't always take that as read!!

[Hsing-ee]

Webley used it on Vulcan and others. A friend of mine bought one for his 77 and it was as you describe above. The guns I have ptfe in have simple flat washers that replaced leather cup washers. Maybe that could be the difference. That and the cylinders are true (possibly).
Out of interest what gun did you try ptfe in?
Dave

I think the Webley washer was different from the usual 'slice of PTFE rod' that PTFE usually means, and it certainly worked quite well. I have a vague memory it was not used to actually seal the piston though.

I tried PTFE in a very nice HW35 Export. The instructions were to dry fire it several times and it would 'mould itself to the cylinder'. It didn't, it was just nasty and slammy. Perhaps they work in a super-true cylinder like from an HW77, but as a replacement for the HW's leather washer it was a disaster. That rifle was super-accurate with the leather washer and made 10.5 fpe in .177, wish I hadn't sold it ...

[Jimny4x4]

Polyurethane elastomer seals are by far the best. Having "memory" resilience they can take a pounding and keep their shape. I make my own on a lathe and seen old rifles improve after fitting replacements. Having a thin lip parachute design gives the best results. Most manufacturers today use polyurethane.

Baz

Benelli B76 - Where do you buy the raw material ? Am interested .

[Benelli B76]

Benelli B76 - Where do you buy the raw material ? Am interested .

There are various diameter rods advertised on the evil bay. Just search polyurethane rod. Be careful some companies charge a lot more than others. May be best just to google it and find the original suppliers.

Baz

[jonnyone]

I think the Webley washer was different from the usual 'slice of PTFE rod' that PTFE usually means, and it certainly worked quite well. I have a vague memory it was not used to actually seal the piston though.

I tried PTFE in a very nice HW35 Export. The instructions were to dry fire it several times and it would 'mould itself to the cylinder'. It didn't, it was just nasty and slammy. Perhaps they work in a super-true cylinder like from an HW77, but as a replacement for the HW's leather washer it was a disaster. That rifle was super-accurate with the leather washer and made 10.5 fpe in .177, wish I hadn't sold it ...

Yes that's the same result as I've had on the HW35L above. Not the best
I think I was warned that older HWs have a slight taper towards the port end and it conforms to this smaller diameter and is slack in the larger section. I vaguely recall I used it in a 35e with better results but there have been converters available for them for a while so I will get around to swapping them over to OEM soon.
Dave

[jonnyone]

There are various diameter rods advertised on the evil bay. Just search polyurethane rod. Be careful some companies charge a lot more than others. May be best just to google it and find the original suppliers.

Baz

Is that the same as OEM seal materials or better Baz?
Do you think its possible to machine a seal to fit on Diana piston heads or would that have to be injection moulded due to the dovetail shape of the retaining stud? Or would it be better to dispense with that fitting arrangement and do a different design?
I'm
very interested in this aspect of air rifle improvement but I have neither.the knowledge, skill, or.equipment to pursue this myself
Dave

[Drew451]

Probably because the transfer port is large, to allow for the sedate leather-braked piston speed...

I think you may be correct. Or surely we would have synthetic sealed 45's etc coming out of Rastatt by the mid 80's. I bet there were trials but the cost of re-engineering the 45* for synthetic seals was prohibitively expensive. In fact the guns were already too expensive to make by then hence the release of 34 series.
*Mind you it wasn't long before they started with the transfer port restrictors.

[Benelli B76]

Is that the same as OEM seal materials or better Baz?
Do you think its possible to machine a seal to fit on Diana piston heads or would that have to be injection moulded due to the dovetail shape of the retaining stud? Or would it be better to dispense with that fitting arrangement and do a different design?
I'm
very interested in this aspect of air rifle improvement but I have neither.the knowledge, skill, or.equipment to pursue this myself
Dave

Dave, the PU rod I buy works as good as factory supplied and is available in similar hardness as measured with a Durometer at 90 to 95 Shore A scale. I have made seals for the Original 6 M pistols with the dovetail taper fitting just by setting up cutting tools as required on my little Emco Compact 5 lathe. Making PU replacement seals for leather ones in old classic air rifles like the Bonehill Brittania and others sometimes gives up to a 100 fps increase in power. Obviously you have to get a good fit, neither too tight or too lose. Having a thin undercut lip on the edge of the seal helps it seal in the chamber bore under compression.

Baz

[jonnyone]

Dave, the PU rod I buy works as good as factory supplied and is available in similar hardness as measured with a Durometer at 90 to 95 Shore A scale. I have made seals for the Original 6 M pistols with the dovetail taper fitting just by setting up cutting tools as required on my little Emco Compact 5 lathe. Making PU replacement seals for leather ones in old classic air rifles like the Bonehill Brittania and others sometimes gives up to a 100 fps increase in power. Obviously you have to get a good fit, neither too tight or too lose. Having a thin undercut lip on the edge of the seal helps it seal in the chamber bore under compression.

Baz

You lost me with the hardness scale. But I certainly understood the benefits you mention there.
That sound like a real benefit to some of these classic guns. Increasing the efficiency and then reducing spring input to drop cocking effort, wear n tear and improving the shot cycle. Sounds like a win win to me.
I would be guessing that you make these seals bespoke to each gun or can you make them based around known manufacturers dimensions and tolerances?
I'd like to try one on my .177 50T01 in the future should you be.interested in a small project? For a sum of course! Only thing is on the T01 is that the existing leather head is riveted on and would need to be turned off and drilled/ tapped. Nothing to a man of your capability but a non starter for a wood butcher
Good stuff mate.
Dave