I never knew that O ring piston seal is not new technology

I never knew that O ring piston seal is not new technology

Joined: January 3rd, 2011, 4:42 am

June 25th, 2012, 11:31 am #1

Please click the following link. I just read it. I think our friend Hector has fine tuned it.

http://www.network54.com/Forum/79537/th ... ons+-+PICS


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RedFeather
RedFeather

June 25th, 2012, 11:45 am #2

The Osprey, for one, uses them.
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baldwin
baldwin

June 25th, 2012, 4:01 pm #3


my bsa mercury manufactured in 70, had an 0 ring on an alumunium head attached to the piston. geting the right sized 0 ring was an issue... had to work on the groove on the head to get the right fit, finally replaced the 0 ring with a teflon seal.

but i do remember the 0 ring shooting experiance was more pleasent.
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Joined: February 21st, 2009, 1:31 pm

June 25th, 2012, 7:42 pm #4

The Osprey, for one, uses them.
Hi RedFeather

Sorry to correct you but the Osprey used two copper impregnated PTFE (Teflon) piston rings, not O rings.

This setup was used on the Webley Hawk MK 2 and 3 as well.




All the best Mick
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RedFeather
RedFeather

June 26th, 2012, 12:34 am #5

Same principle, different materials?
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Joined: February 21st, 2009, 1:31 pm

June 26th, 2012, 7:07 am #6

And I must apologize, though the PTFE piston rings used by Webley did not give crush as PTFE has no physical memory, so not quite the same principal.

The rings used to just sit in the piston groove and wear out, this is probably the best example of how not to use PTFE in a gun.

Since I wrote the article posted in the OP by Umair a lot of folks in the UK have tried the O ring conversion I described on Webley Hawks with some success.

The earliest use of piston rings by Webley that I know of is the the brass piston rings used in the Webley MK2 service rifle from the 1930s.


Anyway I'm still O ringing everything in sight and as we're on the Diana forum, here is my latest build up --- a 12ftlbs Bam b2, which as you know is based on the Diana 25.


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I did cheat a bit with the internals as I used a BSA Meteor piston and trigger.


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And I did have to alter the cylinder a little to accept the Meteor trigger group and front stock mounts.


[/IMG]




All the best Mick
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Joined: July 24th, 2010, 1:44 am

June 28th, 2012, 1:59 pm #7

Please click the following link. I just read it. I think our friend Hector has fine tuned it.

http://www.network54.com/Forum/79537/th ... ons+-+PICS

that I was onto something new when I posted my "revolution" in airgun sealing back in 2004 after fiddling with cutting my own urethane piston seals that would burn out with a few thousand shots. I was posting about my piston seal problems when I was being heckled by LD with this reply "No, its a bit more like the fellahs that try to re-invent the wheel", to which I replied
http://www.network54.com/Forum/79537/me ... NING+wheel!

I still puttered with cutting urethane parachute seals till both my brother and I had "1 inch at 20 yard" poi shifts during one early spring field target match when we were doing the sight-in during snow flurries, but the daytime temp rose to the mid 50s during the match. It was then that I started looking for a way to minimize the amount of "rubber & lube" sliding along the receiver ID. I thought that perhaps changes in seal durometer and lube viscosity due to temperature shifting was the culprit, and that perhaps sealing with a 1/16" cross section oring in a machined piston cap that replaced the "rubber" piston seal would help. My main purpose for trying oring sealed piston cap was to minimize temperature induced poi shifts and the oring sealing I used did alleviate the problem to a great degree. Matter of fact, as posted here a while back I've even gone to using dry graphite powder as a non-dieseling piston seal lube and it has worked splendidly so far. Matter of fact, at the last DIFTA field target match I hit about 88% of the targets shooting hunter class (sitting on a bucket using cross sticks) using my oring sealed/dry graphite lubed oring sealed HW77 springer and actually scored "match high". LOL, I don't expect that to happen again! Here's a post of the match scores.........
http://www.network54.com/Forum/451309/m ... ch+results

Thanks for posting the article, I really enjoyed reading it!

I do use a smaller cross section oring with less oring compression and closer fitting "oring to groove" fit than that posted article. I've learned from trial and error that the amount of oring squeeze and oring cross section has an effect on both velocity and "poi shifting" so I've refined my oring seal geometry over the years. Too little compression and the seal doesn't work very well with loose tolerance receiver IDs, and too much compression gives a lot of oring "stickshun",reduced velocity, and less consistent muzzle velocity. A nice advantage of a well fitted oring seal is the increase in velocity without resorting to more preload or a heavier spring, and this permitted me to use an old light wire Maccari E1500 spring (.120 wire) to get an easy cocking CPL velocity of around 860fps (actually, about the lowest velocity I can get with the oring seal) with little gun motion! Another thing that I've noticed when converting pistons to oring seals is that often the factory piston seal retaining flanges-and-or tapped holes aren't in the exact center of the piston face. This really messes up my "oring to receiver ID fit". Long ago I made it a practice to fit the oring sealed cap snugly on the piston and then lathe cut the cap to fit the receiver with the piston chucked in the lathe to maintain some sort of concentricity of cap to piston shell. For the screwed on piston cap conversions like leather sealed HW55 pistons I even make an alignment mark on the cap and piston body so the cap can be replaced in the same relative position if removed. Perhaps a workaround for this is to build in some slop between the cap and piston body to compensate, however I prefer the "machine the cap while tight fitted to the piston in the lathe chuck" method. After fitting the piston cap to the receiver ID I cut the oring groove for the proper compression, again while the piston is being turned in the lathe chuck. If I remove the piston from the lathe for checking receiver fit, I use a dial indicator to re-center the piston in the lathe chuck to .002 MAX total indicator runout before adjusting the cut. Kinda pain in the butt to do it this way but I'm pleased with the results!

IMHO.....if there is a downside to oring sealing it's the fact that the shot cycle is snappier than factory parachute sealing (almost ram like) and I do prefer the softer shot cycle of a parachute style seal, however I haven't found a factory OR aftermarket piston seal that shoots as consistently as my oring seals. A while back I tried an aftermarket seal in my R9 from relatively new supplier and I really liked the shot cycle it gave, better shot consistency than a factory seal, and not having to mess with the tedious cutting and fitting of an oring sealed piston cap.........however, I did return to the oring sealed piston cap since it's just plain gives a more consistent performance over varying atmospheric conditions.


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Joined: February 21st, 2009, 1:31 pm

June 28th, 2012, 8:15 pm #8

Take it from me my reference in the article to folks in the US experimenting with O ring piston seals is a direct reference to yourself and Hector's work.

I was converting guns to O rings from 1973 onwards and never thought much about it, it was just a means to an end for me.
In about 1982 Cardew published an article in Airgun World called Zap Pow in which he showed that an O ring piston seals friction hardly altered under the sort of pressures found in a springers cylinder, which explains why converted guns feel quicker.
Then in 1991 an article by John Bowkett appeared in Airgun World showing his 12ftlb HW77 field target tune which involved a shorter stroke and a twin O ring piston head --- this is when I realised that I wasnt on my own in my use of O rings.

My use of 70 shore 1/8 section O rings came about as that was the section used by BSA from the early 1970s so I just followed suit. Working at 12ftlbs as we do here in the UK the stickshun you mention can be used to advantage in softening the firing cycle but still giving velocity variations measured in single figures.
I have recently been experimenting by reducing transfer port diameters in O ringed guns to increase the static compression ratio and smooth out the firing cycle --- so far this also seems to have an added side effect in that the velocity variation seems to get smaller.


http://www.airgunbbs.com/showthread.php ... -And-Rusty


When my O ring article was published I to was attacked on open forum but I stood my ground as I was happy that what I had written was true. Since then another UK tuner has combined my work with O rings with his own PTFE bearing work and is having great success with short stroking springers with this configuration.




All the best Mick


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Joined: July 24th, 2010, 1:44 am

June 29th, 2012, 3:02 am #9

Here in the "States" I would need to clip a few coils, use a different spring, or some short stroke work around to get down to 12fpe with an oring seal in my HW77. A while back I did use a "shorter/weaker" spring than the old E1500 and got my .177 HW77 velocity down to 800fps with 7.9 grain pellets and the shot cycle was really sweet. The wind drift however at about 11.5fpe was a bit too much at the field target matches with my shooting skills so I upped the CPL speed to 860fps which has worked fine.

Yep....they are always a few "nay-sayers", however if the results are an improvement over what was being used previously then I just chuckle and shoot "my way" anyhow!

Regards,
Ed
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Joined: March 26th, 2004, 11:28 pm

June 29th, 2012, 3:07 pm #10

Please click the following link. I just read it. I think our friend Hector has fine tuned it.

http://www.network54.com/Forum/79537/th ... ons+-+PICS

"Great minds think alike". Aside from Hector's pistons, I wonder if anyone has tried to market some sort of conversion kit that would replace a parachute seal using the existing piston?

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