GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: mst3kpimp on November 12, 2014, 10:32:13 PM
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Any experience with this? I'm looking to replace the little oring in my Benjamin pump as well as a bolt probe on my Hammerli 850. I see at my harbor freight tools they have viton "brown" and hnbr "green" ring kits.. what should I get and why?
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hbnr is better quality IMO.
Josh
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Buna-nitrile is generally better in terms of abrasion resistance compared to Viton. The advantage that Viton has in the world of airgunning is it is not permeable to CO2 like Buna-N...which of course is not a factor in the two applications you cited.
However if you are referring to the -007 O-ring on the innermost piston of the Benjamin pump, spring for 90A polyurethane. It has best abrasion resistance of commonly available materials.
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Buna-nitrile is generally better in terms of abrasion resistance compared to Viton. The advantage that Viton has in the world of airgunning is it is not permeable to CO2 like Buna-N...which of course is not a factor in the two applications you cited.
However if you are referring to the -007 O-ring on the innermost piston of the Benjamin pump, spring for 90A polyurethane. It has best abrasion resistance of commonly available materials.
http://www.amazon.com/007-Polyurethane-O-Ring-Durometer-Translucent/dp/B0053UOSKK (http://www.amazon.com/007-Polyurethane-O-Ring-Durometer-Translucent/dp/B0053UOSKK) Is this the right one? does anyone have em cheaper?
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That is exactly the package I bought a year ago and they've been good O-rings.
Otherwise a lot of people recommend http://www.theoringstore.com (http://www.theoringstore.com). You can piecemeal single quantities of various O-rings and have them shipped for $5.
http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_459_458&products_id=16198 (http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_459_458&products_id=16198)
or
http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_1322_1327&products_id=27548 (http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_1322_1327&products_id=27548)
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http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm (http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm)
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Buna-nitrile is generally better in terms of abrasion resistance compared to Viton. The advantage that Viton has in the world of airgunning is it is not permeable to CO2 like Buna-N...which of course is not a factor in the two applications you cited.
However if you are referring to the -007 O-ring on the innermost piston of the Benjamin pump, spring for 90A polyurethane. It has best abrasion resistance of commonly available materials.
This part of your statement is not true. Viton o-rings are NOT compatible with CO2 unless it is compound Viton-GF. and those are not very common as standard shelf items except for specialty products.
Regarding abrasion resistance will depend on hardness more than anything, but HNBR o-rings are very common in air systems for their longevity of service. Viton's big advantage is its heat resistance capabilities. I build high pressure gas systems for a living and we always use viton when we can because our equipment gets pretty hot in compressing gasses. ALWAYS Lubricate with silicon grease when installing them.
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Thanks for clarifying the point regarding CO2 permeability against specific formulations of Viton. It's apparently a fine point not commonly understood, having seen multiple sources stating Viton is suitable for seals in CO2 rifles.
Are you saying, though, that one would be better off using either HBNR or Viton over polyurethane in this application, assuming they were all the same durometer and reasonably similar quality material?
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Buna-nitrile is generally better in terms of abrasion resistance compared to Viton. The advantage that Viton has in the world of airgunning is it is not permeable to CO2 like Buna-N...which of course is not a factor in the two applications you cited.
However if you are referring to the -007 O-ring on the innermost piston of the Benjamin pump, spring for 90A polyurethane. It has best abrasion resistance of commonly available materials.
Problem is that polyurethane orings have about the poorest resistance to heat and melt easily. When I used to cut my own piston seals from urethane rod one of my "tricks" was to heat a bolt head and apply it to a puck of polyurethane. The heat of the bolt would melt the surface of the polyurethane puck forming a "glue" that when cooled allowed me to chuck the bolt in the lathe and directly machine the seal.
The temperature range of polyurethane is -20° to +180° F. I guess that if a high pressure pump were operated very slowly as to not form a lot of "air compression heat" the benefits of wear resistance might be useful. I do know that even when I use my tire pump to pump the tire up to only 40 psi the pump tube itself gets noticeably warm! On the other hand, the Viton temperature range is -15° to +400° F. Also, where a 020 size polyurethane oring might cost $13 for (5)....the same size Viton oring costs about $6.50 for (25).
Anywhoo....I use home turned oring sealed piston caps in my R9 and found that the abrasion resistance of Viton is just fine with a properly finished and lubed receiver ID with the oring lasting longer than a good aftermarket main spring.
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Ed, what are you doing in here? Is there something you need to tell us? This is a safe place. We will not judge you. Haha ;D ;D ;D
I agree with your reasoned benefits of Viton's superior temperature rating versus polyurethane's superior abrasion resistance. Maybe it was due to unseen variables but I did not get good longevity the one time I used a Viton O-ring in a high-pressure pump. As I read around, the general consensus seemed to be that polyurethane was the recommended material in this application so, looking at materials properties, I reasoned that it must be abrasion rather than heat that dictated longevity for this particular usage. Granted I limit myself to 60 strokes per pumping session so maybe that keeps heat to a reasonable enough level.
For a piston seal, I can see where heat tolerance may be more important. Certainly for a springer which detonates. I'm not so sure about the adiabatic heating of a normal (non-detonating) compression stroke. What I know about that can fit into a thimble but I thought it was an extraordinary temperature well over 1000°F but which has almost no thermal energy since it exists only in the air molecules. If I'm not totally off-base with that understanding, the heat resistance of the seal really shouldn't be all that critical unless it's detonating a lot.
Just thinking out loud!
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I have a line of gas boosters that uses a combination of viton and UHMWPE (ultra high molecular weight polyethylene) seals for non-aggressive gasses that have pressure capabilities as high as 22,500psi, but the barrels of the boosters are cooled by the drive air (they are air driven). I also have electro-hydraulic boosters that g as high as 100,000 psi with a combination of polymers, leather and silicon, but again the barrels are cooled, in this case usually chill water. With friction and heat of compression, without cooling, they would self destruct in minutes. We try to keep the seal sets below 200F.
For air or nitrogen, Viton would be my choice of o-rings lubed with silicon grease. They have been shown to be very dependable, long lived and will remain supple and not brittle for a long period. They also have excellent memory properties. One of the biggest issues with o-rings is permanent deformation when not in use for long periods of time (for dynamic seals)... static o-rings are not as critical. Their big issue is plastic-cold flowing (and this is sometimes an issue with polymers more so than elastomers. For the static o-rings, a 90 duro hardness will give excellent life. for the dynamic seals in a high quality finished part, the 70 duro seals will give generally the best life, especially if there is a back up used. The back up can be hard nylon, leather or other more rigid material to prevent extrusion.
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Not an argument ... just an observation :o
This past couple years having owned 3 M-rods using #118's to seal the tube, valve & fill cap was using VITON rings sourced from McMastercarr. Doing frequent dismantles while my R&D was active had noticed Time & Time Again upon dismantling the o-rings were noticeably swollen and had grown in diameter ??? .... a hour or so later back to @ OEM size specs.
Obviously the HPA or a single gas ( Co2 perhaps ) had migrated into the matrix of the Viton compound swelling it up.
An observation made FWIW 8)
Scott
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Ed, what are you doing in here? Is there something you need to tell us? This is a safe place. We will not judge you. Haha ;D ;D ;D
I agree with your reasoned benefits of Viton's superior temperature rating versus polyurethane's superior abrasion resistance. Maybe it was due to unseen variables but I did not get good longevity the one time I used a Viton O-ring in a high-pressure pump. As I read around, the general consensus seemed to be that polyurethane was the recommended material in this application so, looking at materials properties, I reasoned that it must be abrasion rather than heat that dictated longevity for this particular usage. Granted I limit myself to 60 strokes per pumping session so maybe that keeps heat to a reasonable enough level.
For a piston seal, I can see where heat tolerance may be more important. Certainly for a springer which detonates. I'm not so sure about the adiabatic heating of a normal (non-detonating) compression stroke. What I know about that can fit into a thimble but I thought it was an extraordinary temperature well over 1000°F but which has almost no thermal energy since it exists only in the air molecules. If I'm not totally off-base with that understanding, the heat resistance of the seal really shouldn't be all that critical unless it's detonating a lot.
Just thinking out loud!
Heat eroded R9 piston seals.........
(http://www.snapagogo.com/uploads/source/2262014/1408104065_1920375418_ErodedR9seal.jpg) (http://www.snapagogo.com/photo.php?id=55759)Uploaded at Snapagogo.com (http://"http://www.snapagogo.com")
(http://www.snapagogo.com/uploads/source/2262014/1408104061_1677608765_seal002.jpg) (http://www.snapagogo.com/photo.php?id=55758)Uploaded at Snapagogo.com (http://"http://www.snapagogo.com")
Notice that the area of the piston seal at the transfer port is eroded by a combination of high heat and the high velocity air jet squirting through the port. At the same time the sealing edges of the piston seals are still intact. When I was using my home turned urethane seals I used one long enough for the velocity to start degrading and an inspection showed that the whole surface of the seal was cratered and even the sealing edges were hardened.
Still......I have absolutely NO experience with high pressure pumps so perhaps my ramblings about piston seals are of no import! It does seem to me that a sub 200degree service limit would have bearing on the use of polyurethane for a high pressure pump seal. The R9 compression chamber generates less than 3000psi and then only for a couple milliseconds yet the piston seals car erode at the transfer port.
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Just stopping back in for an update based on a recent experience with the -007 O-ring on the Benjamin pump. I had previously recommended polyurethane for this application, and Charlie and Ed stepped in with a good point about this material's low melting point compared to Viton.
Shortly after we had this discussion, I decided it was time to go into my pump and deal with a little aggravation I had been having. It seemed the bottom check valve had too much spring force, causing me to be unable to collapse the pump fully after opening the bleed valve. In other words, it was acting like there was still air trapped at the bottom of the high pressure stage (the innermost piston), so when I would push the handle down for storage, it would tend to just jump back up. It was about to drive me nuts so I pulled it apart and installed a weaker spring, and while I was in there I figured I might as well clean and relubricate and, oh yeah, try a Viton O-ring on the inner piston. The clear polyurethane O-ring looked fine in terms of its shape and its flexibility but it had yellowed a bit, so off with it and on went a Viton.
After reassembly, I was pleased to find the weaker spring had solved the problem I was having. It also eliminated the weird squeaking sound that the pump had always made at the bottom of the compression stroke. So over the course of the last 2 weeks, the pump was much more enjoyable to use. Felt great and pumped great.
Then last week the darn thing started acting up. Hard to pull up the handle, and sometimes after pushing it down, it would shoot back up on its own. So on Friday evening after work, I opened it up to have a look. I was shocked to find the Viton O-ring missing about half of its cross section on one side. I could not really tell if it had abraded, melted, or extruded out. In hindsight, I should have studied it more closely and took some closeup photos but alas it is gone with the trash.
So I installed a fresh polyurethane O-ring and reassembled it. Hopefully it will be as robust as the last.
In the interest of full disclosure, the Viton O-ring was rated 75A hardness and the polyurethane 90A. That may have contributed to the Viton's early demise so just take this for what it is, a single anecdotal experience.
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Just stopping back in for an update based on a recent experience with the -007 O-ring on the Benjamin pump. I had previously recommended polyurethane for this application, and Charlie and Ed stepped in with a good point about this material's low melting point compared to Viton.
Shortly after we had this discussion, I decided it was time to go into my pump and deal with a little aggravation I had been having. It seemed the bottom check valve had too much spring force, causing me to be unable to collapse the pump fully after opening the bleed valve. In other words, it was acting like there was still air trapped at the bottom of the high pressure stage (the innermost piston), so when I would push the handle down for storage, it would tend to just jump back up. It was about to drive me nuts so I pulled it apart and installed a weaker spring, and while I was in there I figured I might as well clean and relubricate and, oh yeah, try a Viton O-ring on the inner piston. The clear polyurethane O-ring looked fine in terms of its shape and its flexibility but it had yellowed a bit, so off with it and on went a Viton.
After reassembly, I was pleased to find the weaker spring had solved the problem I was having. It also eliminated the weird squeaking sound that the pump had always made at the bottom of the compression stroke. So over the course of the last 2 weeks, the pump was much more enjoyable to use. Felt great and pumped great.
Then last week the darn thing started acting up. Hard to pull up the handle, and sometimes after pushing it down, it would shoot back up on its own. So on Friday evening after work, I opened it up to have a look. I was shocked to find the Viton O-ring missing about half of its cross section on one side. I could not really tell if it had abraded, melted, or extruded out. In hindsight, I should have studied it more closely and took some closeup photos but alas it is gone with the trash.
So I installed a fresh polyurethane O-ring and reassembled it. Hopefully it will be as robust as the last.
In the interest of full disclosure, the Viton O-ring was rated 75A hardness and the polyurethane 90A. That may have contributed to the Viton's early demise so just take this for what it is, a single anecdotal experience.
My first thought before reading your "durometer choice" was that you were getting oring extrusion and that is usually a situation of too low durometer, too much clearance between piston and cylinder, or both. As the clearance between the piston and cylinder increases the durometer of the oring needs to increase. LOL....in some high pressure applications backing rings are installed to keep the oring from extruding, but the oring gland must be cut to accommodate the backing ring.
Actually, polyurethane is a very tough and wear resistant "rubber" with the only downside being the low melting temperature. As long as the compressed air in your pump doesn't exceed about 180 degrees for a long period of time the polyurethane oring should work well. Perhaps the metal gland the oring is working in is drawing off the heat fast enough that the oring temp remains reasonable, but I really don't know.
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Yeah, extruding was also my best guess as to how it would fail so soon. I would have expected as much had it been a 60A but I figured the 75A would have fared at least better than roughly 10 rather sedate pumping sessions. It's what I had on hand so figured I would try it. Next time I go in, I'll get a small bag of 90A Viton and try again.
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Any experience with this? I'm looking to replace the little oring in my Benjamin pump as well as a bolt probe on my Hammerli 850.
I'd stay away from any Harbor Freight kits. What I've seen is they are under spec and under quality.
The 007 o-ring in the benji pump that often fails from overheating is best replaced with a viton o-ring. Many who have done the swap said it was the last time they had to do the otherwise frequent swap often required with the stock (buna) o-rings that melts when it gets hot from pumping. I'm not sure 90 duro is good because they are VERY stiff and may not stretch over the pump tube. 70 duro or maybe 80 should be fine.
For the Marauder rifle breech o-ring, the urathane is the ticket and it may be for your Hammerli (which I am not familiar with) as well. It will handle the abrasion and you may not have to replace it for a very long time.
For your Marauder air tube, stick with 70 durometer buna (Crosman uses 80 duro for stock, but 70 is more common and just as good). They seal well and are easy to install as long as you lube them with silicone grease. If you go to 90 duro o-rings, you will find insertion of the parts into the airtube becomes a major pain as does movement of the parts after they are inserted.
As others have stated, hardness gives more abrasion resistance, but once you get your parts installed in the airtube, they get no abrasion. Trick is to cover the gauge hole with your lubed thumb while pushing parts into the tube with a wood dowel will prevent the o-ring on the valve or gauge block from popping out the gauge hole where it may get pinched and therefore ruined.
This place is great and the prices are very good http://www.theoringstore.com/ (http://www.theoringstore.com/) I believe they have a minimum order, so you can stock up on sizes you need most.
Ray
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just ordered some o-rings for my 13xx :-* $16.98 shipped 8) i think i got enough to last me over a decade ;D :-*
http://www.theoringstore.com/index.php?main_page=index&cPath=367_79 (http://www.theoringstore.com/index.php?main_page=index&cPath=367_79)
33 x 006 V75 VitonŽ Fluorocarbon Black O-rings 006 V75 VitonŽ Fluorocarbon Black O-rings $0.99
33 x 003 V75 VitonŽ Fluorocarbon Black O-rings 003 V75 VitonŽ Fluorocarbon Black O-rings $0.99
20 x 012 V75 VitonŽ Fluorocarbon Black O-rings 012 V75 VitonŽ Fluorocarbon Black O-rings $1.00
100 x 111 V75 VitonŽ Fluorocarbon Black O-rings 111 V75 VitonŽ Fluorocarbon Black O-rings $9.00
BTW ..... do 0-rings have a shelf life ?
should i just keep them in a ziplock baggie ?
or should a drop or 2 of secret sauce/lube be added and worked around to keep them very slightly damp ?
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just ordered some o-rings for my 13xx :-* $16.98 shipped 8) i think i got enough to last me over a decade ;D :-*
http://www.theoringstore.com/index.php?main_page=index&cPath=367_79 (http://www.theoringstore.com/index.php?main_page=index&cPath=367_79)
33 x 006 V75 VitonŽ Fluorocarbon Black O-rings 006 V75 VitonŽ Fluorocarbon Black O-rings $0.99
33 x 003 V75 VitonŽ Fluorocarbon Black O-rings 003 V75 VitonŽ Fluorocarbon Black O-rings $0.99
20 x 012 V75 VitonŽ Fluorocarbon Black O-rings 012 V75 VitonŽ Fluorocarbon Black O-rings $1.00
100 x 111 V75 VitonŽ Fluorocarbon Black O-rings 111 V75 VitonŽ Fluorocarbon Black O-rings $9.00
BTW ..... do 0-rings have a shelf life ?
should i just keep them in a ziplock baggie ?
or should a drop or 2 of secret sauce/lube be added and worked around to keep them very slightly damp ?
Perhaps this will help.........
https://www.oringsusa.com/html/shelf_life.html (https://www.oringsusa.com/html/shelf_life.html)
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"Fluorocarbon (VitonŽ) FKM Unlimited"
thank you sir :)
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I used Aflas 80A in my Hill pump. Aflas can handle slightly higher temps than Viton. Seems to be holding up just fine.
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my o-rings arrived today :)
only 5 days shipping time including the weekend ;)
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After reassembly, I was pleased to find the weaker spring had solved the problem I was having. It also eliminated the weird squeaking sound that the pump had always made at the bottom of the compression stroke. So over the course of the last 2 weeks, the pump was much more enjoyable to use. Felt great and pumped great.
are you still using the same spring? if so, do you have any other information about the spring you installed? I would like to eliminate that noise. I would like to eliminate that noise too.
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Yes, the lighter spring is still installed and working great. Sorry, I didn't measure it...I just rifled around through my Sour Cream Container O' Springs until I found something that would just barely press the bullet-shaped check valve against its seat when the brass plug was screwed in. Back pressure from the outlet takes care of the rest.
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Yeah, extruding was also my best guess as to how it would fail so soon. I would have expected as much had it been a 60A but I figured the 75A would have fared at least better than roughly 10 rather sedate pumping sessions. It's what I had on hand so figured I would try it. Next time I go in, I'll get a small bag of 90A Viton and try again.
forgot to ask which oring would you recommend? im getting vacuum on the upstroke on my Benjamin pump. I will be taking it apart and cleaning it soon. is the polyurethane holding up?
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I had good longevity from the 90A polyurethane until finally burning it up while pumping _really_ fast, pumping a rifle from zero that had a leaky valve seat. After getting it to 500psi or so, it sealed but the O-ring was toast.
As mentioned, the Viton 70A did not last long at all but it failed due to extrusion rather than heat which leads me to believe a hard O-ring (90A) is most important in this application. So a Viton 90A seems like a good choice, or an Aflas type like Sean recommended.
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is the oring store a $5 flat rate or am I missing something?
http://www.theoringstore.com/index.php?main_page=shippinginfo (http://www.theoringstore.com/index.php?main_page=shippinginfo)
I was thinking of ordering one of each out of three and bulk order the one that lasts longest.
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thats what they charged me .....