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.
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 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!
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.
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.
just ordered some o-rings for my 13xx $16.98 shipped i think i got enough to last me over a decade http://www.theoringstore.com/index.php?main_page=index&cPath=367_7933 x 006 V75 Viton® Fluorocarbon Black O-rings 006 V75 Viton® Fluorocarbon Black O-rings $0.9933 x 003 V75 Viton® Fluorocarbon Black O-rings 003 V75 Viton® Fluorocarbon Black O-rings $0.9920 x 012 V75 Viton® Fluorocarbon Black O-rings 012 V75 Viton® Fluorocarbon Black O-rings $1.00100 x 111 V75 Viton® Fluorocarbon Black O-rings 111 V75 Viton® Fluorocarbon Black O-rings $9.00BTW ..... 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 ?