GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => German AirGun Gate => Topic started by: Kragman1 on November 02, 2024, 01:39:37 PM
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Hi all
From what I've read here and there, replacing a Weihrauch or Diana OEM piston seal with a Vac Seal seems to result in a 20-30 fps gain once the Seal has worn itself in.
Does that track with results that you have seen when changing from OEM to Vac seal?
Thanks!
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ONLY if the tubes size which does vary at the manufacturers level a slight amount happens to not be too large for the VAC seal ?
There is a reason ARH supplies Over Size nearly every seal they make so it can be correctly sized to the Air Tube one is working with.
Don't shoot the messenger ....
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That's the question. Like Scott, I have experienced pretty drastic tube ID variability with my springers. For instance, my 1988 D34 has such a large tube ID that only a 28.9mm seal will seal it, which is larger than most any 28mm piston seal, save for the biggest Diana OEM seals.
I'd like to delve into the Vortek VAC seals for my Dianas, but at a 35 buck actual cost per seal to me, the risk of getting an undersized seal is just too big. Although, having several guns with the same seal type and size the seal would likely find some use...
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Hi all
From what I've read here and there, replacing a Weihrauch or Diana OEM piston seal with a Vac Seal seems to result in a 20-30 fps gain once the Seal has worn itself in.
Does that track with results that you have seen when changing from OEM to Vac seal?
Thanks!
I tried a VAC seal in my HW break barrel and it was OK but it was replaced wit a factory HW piston seal later and I prefer a "GOOD FITTING" OEM seal. The issue with the OEM HW95 piston seals I used was the fact that the diameters varied with some fitting properly and others a bit too loose. I noticed this when a wanted me to "strip the dieseling prone factory lube" and replace it with the non-dieseling Krytox lube I used. When pulling the piston from the receiver his brand new HW95 piston seal seemed "looser than normal" so I replaced it with another brand new HW95 piston seal from my parts bin and it fit the receiver "perfectly snug".
My used VAC seal after a few thousand shots...............
(https://i.imgur.com/xMB5hMJ.jpg)
Good fitting HW95 OEM seal after 1200 shots.........
(https://i.imgur.com/DCnUGNM.jpg)
As a side note, HW piston seal design has been revised over the years like this...........
(https://i.imgur.com/SJBTo92.jpg)
The older "straight base thin parachute configuration" did "not so good up about 30fps velocity" vs the newer reduced base design. Also, notice that the oldest Beeman R9 (rebadged HW95 with different stock) piston seal even had the base of the seal reduced at the factory by grinding.
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I put in an ARH kit + a Vortek seal in my HW95L .22 and the FPS average after about 4K or 5K shots is 720. I don't have good chrono numbers for the before because the factory seal was damaged by dieseling or detonation and I did not have a chrono then. Per recommendations on this forum I also re-lubed with GPL-205, Krytox which seemed to cure the dieseling and although expensive I do recommend it. The rifle is silent cocking with a sharp dull thud for the shot if that makes any sense. Pic of a new Weihrauch seal.
(https://i.imgur.com/Npg4lcLl.jpg)
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I put in an ARH kit + a Vortek seal in my HW95L .22 and the FPS average after about 4K or 5K shots is 720. I don't have good chrono numbers for the before because the factory seal was damaged by dieseling or detonation and I did not have a chrono then. Per recommendations on this forum I also re-lubed with GPL-205, Krytox which seemed to cure the dieseling and although expensive I do recommend it. The rifle is silent cocking with a sharp dull thud for the shot if that makes any sense. Pic of a new Weihrauch seal.
(https://i.imgur.com/Npg4lcLl.jpg)
WARNING This may be a "long rambling" of uninteresting info: ::)
Years ago I started making 6061 T6 aluminum oring sealed piston caps for my HW springers due to factory piston seal erosion at the transfer port and the fact that I got a noticeable velocity jump vs the "HW thin edge parachute seal design" The metal face of the home turned oring sealed piston cap didn't erode and using Krytox for a lube alowed a rather inexpensive 10 cent 75 durometer Viton oring to outlast a good aftermarket ARH spring. As a side note, with the 30+ fps velocity increase over the old design HW piston seal I was able to use a lighter wire ARH spring and still maintain my 880ish FPS with the 7.9 grain die lot marked and dated boxed Crosman Premiers which were my most accurate pellet. Since the boxed CPLs were discontinued a couple years ago I've been TRYING to find a pellet with similar performance and after being disappointed with the consistency of 8.4 grain JSB Exacts (pellet heads were too variable) however I did find that 8.4 grain AirArms were extremely consistent in size and weight even though they were formed at the JSB factory. I also found that the 8.6 grain H&N Field Target Trophy is accurate from both my R9 and HW95 bores.
Anywhoo, I USED to do occasional tuning work on HW springers and I got good performance from proper fitting HW95 piston seals, started using my home turned oring sealed piston caps again. After finding "later design" HW piston seals from customer guns with cracked faces. I don't know the cause of the seal failures be it using loose fitting seals that allowed "slamming", use of "diesel prone lube" or perhaps even HW changing the "rubber compound", etc. Here are a few pics of damaged HW piston seals from a couple "customer guns" compared to the seal erosion I got with the old design HW piston seal (no cracking however).........
Old design HW 95 piston seal erosion at the transfer port......
(https://i.imgur.com/kfIIHga.jpg)
Later design seals with cracked faces...........
(https://i.imgur.com/bwq77JQ.png)(https://i.imgur.com/8GVRR2X.png)(https://i.imgur.com/LuCDbCj.jpg)
(https://i.imgur.com/gRq0z07.jpg)(https://i.imgur.com/R1S6sDD.jpg)
Here is a pic of the first oring sealed piston cap I turned after a thousand shot test to determine if there would be and "impact damage". The cap was still perfectly good with no signs of "slamming", only some residue on the face from the "molly grease" I was using before I "discovered" Krytox grease a couple years later by reading a post by a springer shooter using the stuff..........
(https://i.imgur.com/T0xKCEO.jpg)
Here is the later oring sealed cap design I've been using for few years..........
(https://i.imgur.com/qRSjZd3.jpg)(https://i.imgur.com/JaMH7MG.jpg)
I used to make oring sealed piston caps for friends but found that (as mentioned by others) springer receivers were rather inconsistent on internal diameter and "ovality" which required too much "messin' around" with home made hones to get the geometry suitable for oring sealing. The "flexible nature" of "rubber" piston seals didn't require precise tolerances to seal, however the 020 orings I preferred (1/16" nom cross section) requed much closer tolerances. Matter of fact, some of the early HW receivers I received for oring seal conversion had issues where the person doing the honing seemed to have "fallen asleep" so the receiver was "belled" at the transfer port end to the point that the oring "lost a lot of compression" toward the transfer port. I ended up making a "go-no go" gage to test for internal size before messing with the receiver and these these guns were simply fitted with a proper size new style factory seal. As mentioned, HW newer piston seals from a few years ago (don't know about recently) came in a variety of sizes so there was a seal for every receiver variation if a bit of "comparing seal fit"
Receive internal geometry gage...............
(https://i.imgur.com/JjxZu5W.jpg)
"High Tech" LOL cylinder hone that hones all the way to the transfer port without the a "cylinder hone ridge" of the "wings" of a cylinder hone getting caught in a "cocking shoe slot". The "shell" is simply a length of PVC water pipe lathe turned for a slip fit in the receiver with a wrap of oiled 500 grit "wet of dry" silicon carbide abrasive.........
(https://i.imgur.com/cIw23cq.jpg)(https://i.imgur.com/VfNiwdZ.jpg)
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Yea those pictures of the OEM seal beat battered & burnt I have witnessed as well.
Detonation in the compression space is brutal with the oem seal as there design is flat face creating so much heating of the air as piston is bottoming out you get that result.
ARH "Bullet" seals have a slight concave / recessed compression face that allows seal to bottom out along the outer most edges leaving @ .030-.040" of the mid seal area up off the face of compression chamber when bottomed out. Sure they too will diesel if sloppy with lube, but properly set up and lubed they don't diesel at all. * Also with no mid seal contact the transfer hole does NOT extrude into seals face further damaging it.
What I've found .. your mileage may differ ::)
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Hi all
From what I've read here and there, replacing a Weihrauch or Diana OEM piston seal with a Vac Seal seems to result in a 20-30 fps gain once the Seal has worn itself in.
Does that track with results that you have seen when changing from OEM to Vac seal?
Thanks!
Being, perhaps impolitely, forthcoming; my experience is that there is no better seal material than the "silicone rubber" that DIANA uses.
I've seen seals from all parts of the world, made by different methods, with different geometries/shapes, and I still cannot find an OEM seal that performs better over long runs.
Seals that are 20 years old and tens of thousands of shots are pretty close to "as issued" dimensions. The color changes. From light blue (new/unused) to dark blue to dark blue-green, a bit of flexibility is lost in the "cookout", but as far as sealing is concerned, they still do a smashing job.
Another aspect is that DIANA seals are made by pressure molding a compound that is thermo-fixed, meaning that all the seals are, within industrial tolerances, identical. Something that does not happen in seals that have been turned out of urethane, or other polymer.
You can know when a seal is molded if it has letter imprints, like Walther's or DIANA's. If a seal has no imprints, then it is probably machined.
The ONLY reason why I change from the OEM seals to the ORing seals in our competition/hunting guns is because of thermal stability and "first/cold shot" uniformity. Something that is not important to most shooters.
Even the majority of the hunters, putting three shots into the ground before taking to the stalk/hunt ensures a pretty uniform POI through the day. As far as hunting accuracies are concerned.
One material that was touted as the the "ACME" and the material for the future, was MoS2 nylon, urethane, or other polymer. In the end, the MoS2 actually burned out of the material and created more problems than it solved.
The "doughnut" DIANA seal keeps the center "empty" and allows for a full contact around the perimeter of the compression cylinder. At some point in time the Brits claimed that there was a "lost volume" there also, but as we have found out, the piston does not really "bottom out" on the first approach to the transfer port wall.
I do favour a concavity at the face of the piston, even with the ORing sealing method. It has proven to add stability to the MV.
Bottom line: you can test all the seals you want; in the short run, some will perform better (more efficiently) than others, but airguns are extremely stressed machines, and looking at the long run is a smart strategy.
HTH, keep well and shoot straight!
HM
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Hector,
When did Diana go to the high pressure seals?
My 5G sat for 20 years and when I shoot it after it's hibernation, the seal just disintegrated. :-\ :-[
-Yogi
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Hector,
When did Diana go to the high pressure seals?
My 5G sat for 20 years and when I shoot it after it's hibernation, the seal just disintegrated. :-\ :-[
-Yogi
Kinda off the subject but the older FWB 124 also had issues with crumbling piston seals.........
(https://i.imgur.com/GHWEki5.jpg)(https://i.imgur.com/tDpSBZX.png)
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Hector,
When did Diana go to the high pressure seals?
My 5G sat for 20 years and when I shoot it after it's hibernation, the seal just disintegrated. :-\ :-[
-Yogi
Dear Yogi;
Without better dates, your criticism feels a bit unfounded (Emphasis in "feels").
Now; from "tales from the Crypt" told by old hands at Rastatt, the Nylon seals were "only" used for a couple of decades, meaning the early 60's to the late 70's.
The Giss action guns (rifles and pistols), stopped being produced in the late 80's-early 90's, by then, most were already wearing the blue silicone rubber seals and bumpers.
The D100 Match model (SSP) was amply used in the Atlanta Olympics (1996).
The seals that "cooked and disintegrated" were made of Nylon and, AFAIk, they were replaced in the very late 70's.
That is as close as a time-line I can think of and it is unsupported by documents, this is "hearsay", so take it with a grain of salt.
It still means that you could have bought a 5G made in 1979, and by 1999 (20 years of hibernation AND 25 years ago), the seals could have 'aged beyond redemption'.
Even though DIANA conducted a thorough campaign of "free seals changes" during the late 70's-early 80's, that did not reach across the oceans because the wholesalers/distributors didn't want to bother.
HTH
HM
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Hector,
When did Diana go to the high pressure seals?
My 5G sat for 20 years and when I shoot it after it's hibernation, the seal just disintegrated. :-\ :-[
-Yogi
Kinda off the subject but the older FWB 124 also had issues with crumbling piston seals.........
(https://i.imgur.com/GHWEki5.jpg)(https://i.imgur.com/tDpSBZX.png)
Thanks, Ed!
Yup! Nylon was the "Wunderkraft materiel", and all the airgun makers used it, from FWB, To HW, to DIANA. AND, no one told the chemists that piston airguns function at extremely high temperature and pressure spikes.
What is funny is that MODERN, hard Nylon (6/6) is perfectly capable of withstanding the conditions. It is not suitable for seals because it is very hard, but it does not "cook" like the older Nylon did.
;-)
Keep well and shoot straight!
HM
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Hector,
IIRC-The 5g was purchased in 1981 or 1982.
-Y
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Earlier this year, Just Zack 2 at Airgun Nation wrote this about the Diana OEM piston seals:
"If keeping at full power, expect the OEM piston seal to last about 3000 rounds, but this isn't a "hard" number. Some seals might last twice as long. Just saying at about 3000 pellets in, I'd recommend getting a replacement seal or two to keep on hand."
These kinds of user evaluations give people ideas about aftermarket seals for the Dianas, the best of which last 10's of thousands of rounds.
Having bought and fitted a dozen or so Diana OEM piston seals I have learned their dimensions vary widely, even with this relatively tiny sample. "Identical", they are not.
Vortek seals, impregnated with MoS2, are used by thousands of airgunners, and sworn by many. Outside of Hector's vague claim earlier in this thread, I haven't heard anyone saying the moly "burned out and created more problems than it solved" with these seals.
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Sorry for the late reply, been busy with the World's and all.
Had to do some "archeology" into my bin of "Archived/Old" parts to find some old seals.
Then took a picture of a "chronological aging" set, then took measurements of seals that were made with 40 years difference. Yes 4 decades apart.
Here are the results:
(https://imagizer.imageshack.com/v2/800x600q70/923/XN701i.jpg)
From left to right, seals extracted from:
2020's D34
2010's D54
2000's D45
1980's D48
Now the front, inverse order (right to left):
(https://imagizer.imageshack.com/v2/800x600q70/922/pbehrC.jpg)
Now let's measure them (at the point of initial contact):
2020's seal:
(https://imagizer.imageshack.com/v2/800x600q70/924/AyGJBw.jpg)
2010's seal:
(https://imagizer.imageshack.com/v2/800x600q70/923/tHs7L3.jpg)
2000's seal:
(https://imagizer.imageshack.com/v2/800x600q70/923/WvB6GW.jpg)
1980's seal:
(https://imagizer.imageshack.com/v2/800x600q70/923/T4jX9B.jpg)
And now let's look at the Mfg info on each seal:
2020's:
(https://imagizer.imageshack.com/v2/800x600q70/922/hcl2VU.jpg)
2010's:
(https://imagizer.imageshack.com/v2/800x600q70/924/Th8Xvl.jpg)
2000's:
(https://imagizer.imageshack.com/v2/800x600q70/922/VYETFP.jpg)
1980's:
(https://imagizer.imageshack.com/v2/800x600q70/923/IGhVhP.jpg)
Now, these seals may not be "identical' under some criteria, but for my criteria, they are as identical as a polymer part can be produced, AND as identical as polymer parts can be when separated by time of USE.
Do note that in almost half a century, it's the same manufacturer who is making these seals.
As to the flame resistance of MoS2 filled materials, see this piston head made of MoS2 filled nylon:
(https://imagizer.imageshack.com/v2/800x600q70/922/6kpsXI.jpg)
And that is after ONLY 200 shots!
Hope these pictures put things into perspective.
Thanks for reading, keep well and shoot straight!
HM
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Hi all
From what I've read here and there, replacing a Weihrauch or Diana OEM piston seal with a Vac Seal seems to result in a 20-30 fps gain once the Seal has worn itself in.
Does that track with results that you have seen when changing from OEM to Vac seal?
Thanks!
When I put the VAC seal along with the Vortek OEM plus power spring in my R9 it gained 35 fps using Crosman 14.3 HP's over the stock parts. How much of that was the spring and how much of that was the seal I don't know? (668 fps to 700+ fps)👍