It will be interesting to revisit this topic when the Delta Wolf has been out for a year or so.
Upvote 0
PCP Leaks as a common occurrence...
- Thread starter L.Leon
- Start date
Agree 100% with this statement...
I would only add something to answer L Leon's question about higher end guns failing rate...It has been my experience that it makes NO difference but there are some designs that are better than others. As mentioned in the post before mine, there are systems using static seals and others use more dynamic o-rings and this makes a difference. FX Impact Power Plenum use 2 o-rings for their long main rod/valve and another dynamic one for sealing the valve to the block on top of a Delrin seal for the valve, those seals wear out with friction. By comparison Steyr LG-110 use an o-ring embedded in the frontal section of the valve that compresses for sealing...Friction wears more rapidly that compression. The other dynamic seals in the Steyr are 2 seals in the piston (regulator) and everything else is static sealing pressure. An FX will probably fail 3-4 times faster than a Steyr but both guns are very easy to overhaul, my favorite PCP for overhauling/repairing is the Steyr, you can fully overhaul it is 10-12 minutes in the field with only 2 hex keys and replacing the O-Rings, regulator or valve as necessary.
When using static seals and low BAR settings (Regs set at 55 to 75 BAR) as all ISSF 10 meter guns like Steyr, Anschutz Walther and Feinwerkbau use, those seals last many and I literally mean many years, even the dynamic o-rings in regulators last years before failing; that is not going to happen in a gun shooting 140-150 BAR pressures, but overhauling one of those top of the line guns is much more difficult and requires more equipment and special tools.
Regards,
AZ
Upvote 0
Static O-rings can and do last a long time provided the tolerances aren’t so sloppy that it eventually creeps and extrudes into the gap. The same issue applies if the O-ring durometer is too soft. A harder O-ring will resist extrusion better, but is simultaneously at greater risk of being damaged on installation so those considerations have to made in balance.
Dynamic O-rings, their longevity is influenced by 4 key factors:
1. Material type – how well it sustains abrasion. Polyurethane is tops amongst common materials but Buna-N is no slouch. I often point out the shelf life figures as a consideration too; I think RJ is the only other person I’ve known to shine a light on that aspect.
2. Surface quality – a rough surface promotes faster abrasion
3. Operating pressure – more pressure means the elastomer is being pressed against the surface more forcefully, meaning that it is effectively being ground into dust like someone extinguishing a cigarette on the sidewalk under their boot heel.
4. Durometer – a harder material resists abrasion better
By the way, it has occurred to me that polyurethane’s otherwise negative characteristic of taking a compression set may actually be beneficial to its longevity in dynamic applications. Nonetheless I have used 90 durometer Buna-N’s in regulator rebuilds at times and it’s not obvious to me that it is an inferior material in this application. I still tend to use a polyurethane when I have it but I won’t hesitate to use Buna-N if that’s what I have on hand.
For bolt and breech O-rings, I prefer polyurethane because they are often run dry, they are exposed to environmental contamination that may act as an abrasive, they are exposed to potentially sharp flashing on pellet heads and skirts, they are usually fairly easy to change, and they are likely to fail from use before shelf life becomes a factor.
For everything else, Buna-N.
Dynamic O-rings, their longevity is influenced by 4 key factors:
1. Material type – how well it sustains abrasion. Polyurethane is tops amongst common materials but Buna-N is no slouch. I often point out the shelf life figures as a consideration too; I think RJ is the only other person I’ve known to shine a light on that aspect.
2. Surface quality – a rough surface promotes faster abrasion
3. Operating pressure – more pressure means the elastomer is being pressed against the surface more forcefully, meaning that it is effectively being ground into dust like someone extinguishing a cigarette on the sidewalk under their boot heel.
4. Durometer – a harder material resists abrasion better
By the way, it has occurred to me that polyurethane’s otherwise negative characteristic of taking a compression set may actually be beneficial to its longevity in dynamic applications. Nonetheless I have used 90 durometer Buna-N’s in regulator rebuilds at times and it’s not obvious to me that it is an inferior material in this application. I still tend to use a polyurethane when I have it but I won’t hesitate to use Buna-N if that’s what I have on hand.
For bolt and breech O-rings, I prefer polyurethane because they are often run dry, they are exposed to environmental contamination that may act as an abrasive, they are exposed to potentially sharp flashing on pellet heads and skirts, they are usually fairly easy to change, and they are likely to fail from use before shelf life becomes a factor.
For everything else, Buna-N.
Upvote 0
To be fair do one about Taipans. If the numbers are close then we can compare the amount of posts about them leaking. Or better yet, just try to find one about them leaking.
Upvote 0
I have repaired every gun you've heard of and probably some you haven't. I have found a correlation between the quality of air people use vs how long the Orings last. I have opened guns that felt and smelled like a swamp inside I have noticed an increase in filthy air used in guns around the time cheap compressors entered the market. I'd be curious, of the guys on this thread could chime in, what they use to fill their guns. Before I opened my business I only used Nitrogen, not one leak in 5 years on any brand I had
My point is when you read stuff about "brand x" leaking, sometimes it's not always just the gun.
My point is when you read stuff about "brand x" leaking, sometimes it's not always just the gun.
Upvote 0
Been tinkering with pcp's since about 1993. AZ had some good points as the DESIGN is important but tolerances are important too. Not picking on FX because any manufacturer can have tolerance stacking but one comes to mind that is a friend's Impact. Leaked and couldn't seem to fix it but finally noticed the oring in the reg pocket seemed to not be visible when looking straight down. Replaced it with one slightly thicker and no more leak. The opposite can be true where they are squished in. Orings need about 15% compression from what I've gleaned from various manufacturers references. It can make a BIG difference. Of course, static or dynamic is part of the equation, as well as material selection. Speaking of that, Parker Orings used to have a manual with a table of selection characteristics. Their current one doesn't have this specific table but it contained everything in one table for materials. IF I'm recalling correctly, Buna had a shelf life of 7 years where Viton and Urethane had no limitation. There are many other factors... such as material quality and storage conditions but this is something I've let influence my oring choices. I've yet to see a Viton oring hard as a rock when resealing but virtually every pcp I've resealed from factory that were over 9 years old had seals somewhere that were hard as a rock.... not functional. I'm sure cost and availability are big parts of why they're used, but it's still puzzling to me when better materials are out there. Urethane seems to be the strongest but most expensive of the commonly available ones where Viton is much stonger than Buna, lasts much longer and is more chemical resistant as well as MUCH greater heat rating. Also, the Durometer rating is important. This comes down to tolerances as well as material selection but in general, 70D is recommended for 1000 psi of differential or less where 75D is much higher and 90D is highest. 90D is more difficult to get to seal, so higher differential is more or less required . There is overlap through material selection though, so there ARE options.
Sooo... for me, Viton seems the best general choice with polyurethane for difficult and dynamic uses.
Bob
Sooo... for me, Viton seems the best general choice with polyurethane for difficult and dynamic uses.
Bob
Upvote 0
Bob, FYI those shelf life figures you’re giving for polyurethane and Buna-N are incorrect, though right about Viton being unlimited. That characteristic has continued to tug at me but as I’ve used them, I’ve found they don’t seem to last noticeably longer than Buna-N in practice, and they annoyingly swell under pressure, making it so I either need to be sure I have a replacement on hand or am willing to wait 24 hours to return to their original size before reassembly can be done.
Upvote 0
Right on!!! Air should be pretty clean and dry... Correct lubricant for the seal material is a must...other than breech seals I have been shooting pcps since 83 and never had leaking problems... I can tell you that the first theoben rapid 7 in the us is still only had breech and bottle seal replaced...and a pre mk 1 huntsman never been resealed....I'm sure it will puke tomorrow now... The only new leaker I have ever had to try my last nerve has been a lcs sk-19
Upvote 0
I wanted to add a couple things to this thread, first I was having a issue with one of my airguns and reached out to arzrover because of his knowledge of this airgun which in turn he graciously helped and gave me input and ideas as to any problem areas, now in our conversations this statement caught my attention “ after -X- amount of pellets this is an O-ring we found to be a potential problem ” so that brings me to point 2, regardless of the Manufacturer or O-ring specs., with our own experience and data, maybe we all should look into planed maintenance schedules ( replace all O-rings etc. at one time or upgrade if need be) and I would assume the more O-rings in the design ( static or dynamic ) the more or sooner maintenance schedules will be required? In my field of work scheduled outages are fine, unscheduled or forced outages are not! FWIW!
Upvote 0
This has also been my experience with Viton...ALL of the European ISSF brands use them in static applications and most of the dynamic ones are Poly...The only issue here in the US is that there are some metric sizes that are just impossible to find...Last year I decided to order different non-conforming sizes in different thickness (Viton) and I ended up with a large container full of o-rings I had no use for, then the process of testing that involves disassembling and assembling the gun for every test was not the best idea; I dropped my "Brilliant" idea and opted for acquiring 10 or so factory full overhaul kits for those ISSF guns...More costly but saves much time and frustrations when what you thought was going to work leaks.
One thing I forgot to mention on my last post was the importance of lubricating very thoroughly the o-rings...Silicon grease, silicon oil or even lithium grease all work very well in prolonging the life of the seals, the silicon grease used for scuba diving is very pure and good but what plumbers use for faucets also works OK...Other than my ISSF low power guns (Anschutz 9003 and 9015, FWB 700 and 800 and Steyr LG-110 and two FWB PCP pistols) I've never been fortunate enough to have any gun lasting more than about 1.5 to 2 years before developing an o-ring failure (from small to large leaks)...I shoot: 2 Raws, 2 Impacts, 1 Daystate in power levels requiring reg pressures from 110 to 150 BAR.
The worst enemy of O-rings are UV rays followed by temperatures out of the range of the o-ring's material and of course chemicals which we are taking out of the equation...If any of you ever want to store o-rings for a long period of time, vacuum seal them and put them in a black bag or a non transparent container and keep them at room temperature...We stored them this way at the lab but lightly lubricate them with silicon grease/oil before vacuum sealing them.
Somebody mentioned "Quality of Air"..That is an important variable, those cheap Chinese compressors leak lubricants and toxic gases which are harmful to o-rings, I've never encountered this problem because I use a scuba diving compressor (Bauer Jr II) and I keep the filters schedule for breathable air quality...More costly but in the long term less compressor maintenance and issues and zero problems with rust, dirt and grime inside the air system of the gun...If you can believe this: Bauer calls for 1500 to 2000 hrs. before inspecting/replacing valves and measuring rings wear, I bought the compressor new 3 years ago and it has like 7-8 hours after 2,5 years of heavy use during the summer, this thing tops my White Shark from 3000 to 4500 in about 5 minutes...So at this rate this compressor will be part of my estate for my great great grandchildren for one of them to inspect it!!
I rebuilt a gun for a friend who uses one of those Chinese very cheap compressors and yes, I needed to clean and remove rust and grime all around the air system from cylinder to port...We have large cylinders with Nitrogen at the lab and before the Bauer I considered it for my home and tried it just for the more stable pressures in fluctuating temperatures, but the advantage was not worth the effort of getting the large tank and fixtures inside the garage; after all pure air is roughly about 78% Nitrogen and around 21% of Oxygen, the remaining gases have basically no impact...It is true that tires in racing cars use nitrogen for pressure stability successfully, and airguners have tried to follow the trend...But what has not been said is that racers use nitrogen vs. air for more stable pressures because the 21% oxygen in the air permeates the thin walls of the tires at different rates which causes pressure variations...Oxygen does not permeate our aluminum and titanium air cylinders but I hate to discuss these kind of topics because it hurts some egos not willing to listen or discern with intelligence...The size of the plenum and air cylinder capacity has more impact in variations of pressure derived from changes in temps and of course, the higher BAR setting we use the more prone the gun is to variate its velocities.
I'm going to lunch, will be back later in the afternoon to read further posts...I like what has been discussed in this thread.
Regards to all members,
AZ
Upvote 0
Great point Brian, and one not mentioned on here that I can remember. I can remember filling my gun with another shooter’s SCBA and smelling oil when I vented off the fill rig.
Upvote 0
You are dead on on this one, I opted for completely overhauling my high power guns every 2 years whether needed or not...In the past I had 2 sour experiences: Drove 400 miles each way for a good match and the gun failed while I was on the sighters before even shooting the first bull of the first target (25 M Benchrest)...I drank good coffee and watched a good match...My other experience was worse, at the 2018 Nationals shooting LV with a Steyr I used to lead the national rankings that year, I finished my first target one point behind the leader who won the nationals (Vipha Miller), but she shot in a protected area and I shot in a very windy open section, we were rotating benches so she would later be shooting from that windy position...Shooting my second target at around the 5th bull or so, the gun started hissing badly (next bench could hear it) and loosing pressure immediately after closing the slide...Shooting sighters I figured that I needed to shoot as soon as I closed the bolt...Easy to say but hard to do, especially in windy conditions where you hold for a more steady wind...I finished 4th with a mediocre score that ended up being a tie in 3rd after correcting a sum error, but the issue is that Mr, Murphy likes airguns and if something can go wrong it will go wrong, and it will happen when something important is going on...After that experience I learned my lesson and do as you mention (every 2 years exactly)...Better safe than sorry and even then, there is no guarantee that the guns will hold until the next rebuild.
Lunch is still not ready!
AZ
Upvote 0
What needs to be noted is the amount of sealing surfaces in a particular rifle will add to the opportunities for leaks. The better designs for reliability will have less.
Rob
Rob
Upvote 0
Absolutely, and as somebody mentioned: The surface finish has much to say...Anschutz, Steyr, Walther and FWB all come with mirror finish surfaces with no sharp edges anywhere, some others I shoot came with milling/lathe minute machine marks.
AZ
Upvote 0
https://www.oringsusa.com/html/shelf_life.html
ARP 5316 Elastomer Shelf Life Recommendation
The Society of Aerospace Engineers (SAE) issued Aerospace Recommended Practice (ARP) 5316. It was issued in 1998 to supersede MIL-HDBK-695 as the aerospace industry standard in governing o-rings and molded seals shelf life. ARP 5316 is often used as a guideline in determining useful shelf life of elastomers used in other industries.
Recommended Shelf life
ARP 5316 Elastomer Shelf Life Recommendation
The Society of Aerospace Engineers (SAE) issued Aerospace Recommended Practice (ARP) 5316. It was issued in 1998 to supersede MIL-HDBK-695 as the aerospace industry standard in governing o-rings and molded seals shelf life. ARP 5316 is often used as a guideline in determining useful shelf life of elastomers used in other industries.
Recommended Shelf life
- 5 years: Polyurethane (millable), SBR, Natural Rubber, Polybutadine, Polyisoprene
- 15 years: Nitrile, Neoprene, HNBR, Polyacrylate, Butyl
- Unlimited: Ethylene Propylene, Fluorocarbon, Perfluorinated Elastomer, Silicone, Tetrafluoroethylene Propylene (Aflas®), Fluorosilicone.
Upvote 0
I had a heck of a time getting this info to paste.
You can go to the link for more complete info as well as other tables on set resistance, temp ratings, permeability, toughness, etc.
Nervoustrig.... the data I cited was from memory so might not be accurate and the table here agrees with you. Of note, though, I've had maybe 60 or so different kinds of pcp's since 1993 and only a SMALL number actually made it to 15 years before needing seal replacement. Most were 7 to 9 years. ALL were hard as rock and almost certainly BunaN or Nitrile. I also have several exceptions to the polyurethane life rating, so I'm not so sure about this data, but willing to accept it as stated. I think it was covered well, but fit, material quality, and design or usage all play a big part in the life of an oring.
I'm still learning, though.
Bob
You can go to the link for more complete info as well as other tables on set resistance, temp ratings, permeability, toughness, etc.
Nervoustrig.... the data I cited was from memory so might not be accurate and the table here agrees with you. Of note, though, I've had maybe 60 or so different kinds of pcp's since 1993 and only a SMALL number actually made it to 15 years before needing seal replacement. Most were 7 to 9 years. ALL were hard as rock and almost certainly BunaN or Nitrile. I also have several exceptions to the polyurethane life rating, so I'm not so sure about this data, but willing to accept it as stated. I think it was covered well, but fit, material quality, and design or usage all play a big part in the life of an oring.
I'm still learning, though.
Bob
Upvote 0
So here's the deal with PCP's leaking.... I know it sounds cliche' but a chain is only as strong as it's weakest link. 99% of the time in a PCP, the leak is caused by an o-ring. O-rings are pliable and malleable, and if the size or seal is off by .0001" it's going to leak. I've had LOTS of leaks on my rifle. It's ALWAYS the o-rings. It's not a big deal. It's actually been a great learning curve for me. It's forced me to dissect my rifle and my regulator, and by doing that I've gained understanding of the physics of the rifle as well as gained confidence in my abilities to fix the gun myself.
But in the many o-rings I've replaced, I've become a connoisseur of them. The absolute BEST, longest lasting, most durable o-rings you can buy are Cast Disogrin Polyurethan O-rings. They are made in 70 or 90 durometer. The 90 duro can handle 10,000 psi (690 BAR). Over time they also take on the contour of the space they are sealing- like wax being pushed into a space. They are the BEST! And they last a LONG time! But they aren't cheap. Unfortunately they don't have a huge selection in metric sizes.
If you guys are interested, they can be found at the o-ring store (online). They are located in Oregon. When I order from them, they are on my doorstep in 2 working days. I live in San Diego. Here's the link:
https://www.theoringstore.com/store/index.php?main_page=index&cPath=367_1321 (70 duro standard size)
https://www.theoringstore.com/store/index.php?main_page=index&cPath=367_1322 (90 duro standard size)
But in the many o-rings I've replaced, I've become a connoisseur of them. The absolute BEST, longest lasting, most durable o-rings you can buy are Cast Disogrin Polyurethan O-rings. They are made in 70 or 90 durometer. The 90 duro can handle 10,000 psi (690 BAR). Over time they also take on the contour of the space they are sealing- like wax being pushed into a space. They are the BEST! And they last a LONG time! But they aren't cheap. Unfortunately they don't have a huge selection in metric sizes.
If you guys are interested, they can be found at the o-ring store (online). They are located in Oregon. When I order from them, they are on my doorstep in 2 working days. I live in San Diego. Here's the link:
https://www.theoringstore.com/store/index.php?main_page=index&cPath=367_1321 (70 duro standard size)
https://www.theoringstore.com/store/index.php?main_page=index&cPath=367_1322 (90 duro standard size)
Upvote 0