HW/Weihrauch What a difference a seal makes.

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EMrider

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Jan 12, 2016
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CA, United States
I've been tinkering with tune kits, springs and seals in my springers for more than a decade. No fancy tools and no sophisticated skills, but I consider tinkering to be part of the fun. I just got my first lesson on the importance of a properly fit piston seal.

A few months ago, I bought another .177 hw30s when Krale had them on sale. This was my third hw30s or R7 in .177. It was such a great deal that I'm kicking myself for not also buying another hw50s in .177 🤦‍♂️. This gun sat on my workbench for a few months until a move was completed, and the snow started to melt. A couple of weeks ago I installed a new ARH kit in the gun, removed the factory lubes and applied ultimox 205. My go-to combination is an ARH kit and a Vortek piston seal, but I didn't have a Vortek seal in my spares bin. I replaced the factory piston seal with another 25mm seal of unknown origin (I think it was from Custon Air Seals, but not sure). Snugged everything up, mounted a Hawke Vantage 2-7x32 scope, and then started shooting. I put probably 150 JSB 8.4s through the gun, mainly just plinking pine cones and off hand shooting at targets. It was a delight to shoot, very smooth to cock, and very accurage. I figured that I had a winner, and then pulled out my chrony to record the numbers. First shot was 405fps. Can't be right 🤷‍♂️. Five more shots, all about 405-410fps. What the heck? I knew something was way off, but did not know if it was a problem with the spring or the seals. Went back to my workbench and reinstalled the factory piston seal. Velocity bumped up to about 500fps on average over a dozen shots. Better, but still not right. Back to the workbench, took the gun completely apart and did a thorough check of all parts. Nothing appeared to be amiss.

Next step was to order a couple more Vortek 25mm piston seals. Those arrived today, and I immediately went back to the workbench to install the Vortek piston seal and put everything back together. Put about a dozen pellets (JSB 8.4s) through the gun, and everything felt great as it did before. Pulled out the crony, and the first shot was 625fps. A few dozen more shots over the crony all give me very similar results. Mounted the scope, and accuracy remained excellent. All is now well.

I've never experienced such a wide variance in FPS from changing the piston seal alone. And subjectively, I really did not 'feel' any meaningful difference in the fit of the first seal that shot 405fps and the Vortek seal that shot 625fps. But the chrony reveals the truth that even slight differences in fit (maybe beyond what you can subjectively feel) make a huge difference.

R
 
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Struckat said:
I think the factory/ARH seals need to be fitted.

I’ve tried that without success. Sure I didn’t do it correctly.

I use Vortek seals in my HW95
The factory seal in my 30 is still as good as new, performance wise. But I have a vt to put in there when needed.
Click to expand...
YES ... ARH expressly states to be installed by a knowledgeable / experienced airsmith stating they are oversize requiring sizing & fitment * Which is a Good thing !!
As very few air tubes are the same exact size, perfectly round etc .... So the one size fits all approach is weak by comparison. Tho does fit a nitch for many who self service w/o miens to do a better job starting oversize and fitting comp tube for a perfect fit.

Also seals come in different configurations ( Type sealing edge utilized ) Those undercut being a semi flexing lip and those that are solid on outer edge requiring precision fit, which are generally faster seals, but lack being able to seal well in out of round or tapered comp tubes.

For OP, great to hear your finding success and getting the power wanted (y)
 
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Some ways into my springer fixin' journey I learned piston seal fit can give or take 100 fps just like that, and that springer bore figures such as "26mm", or "28mm", are little more than approximations, as incredible as that sounds. Your gun can actually have a 25.8 or a 28.9mm bore, which obviously makes it impossible for cookie cutter seals to work well.
 
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Motorhead said:
YES ... ARH expressly states to be installed by a knowledgeable / experienced airsmith stating they are oversize requiring sizing & fitment * Which is a Good thing !!
As very few air tubes are the same exact size, perfectly round etc .... So the one size fits all approach is weak by comparison. Tho does fit a nitch for many who self service w/o miens to do a better job starting oversize and fitting comp tube for a perfect fit.t

Also seals come in different configurations ( Type sealing edge utilized ) Those undercut being a semi flexing lip and those that are solid on outer edge requiring precision fit, which are generally faster seals, but lack being able to seal well in out of round or tapered comp tubes.

For OP, great to hear your finding success and getting the power wanted (y)
Click to expand...
Airguns tuning includes many nuances most folks don’t really want to deal with or take time to master.
Piston seal fitment is not one of my strong points, I originally walked away from ARH seals mainly because I didn’t understand Jim’s (need to customize) approach. I thought you just jammed the seal in there and you were done.
 
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SpiralGroove said:
Airguns tuning includes many nuances most folks don’t really want to deal with or take time to master.
Piston seal fitment is not one of my strong points, I originally walked away from ARH seals mainly because I didn’t understand Jim’s (need to customize) approach. I thought you just jammed the seal in there and you were done.
Click to expand...
In the past, I have also not used ARH seals because I'm not comfortable with sizing them myself. After this experience, I'm far more aware of the importance of proper sizing. But, I'm even less confident in my ability to get it right without a lot of trial and error, because I did not 'feel' a big difference in fit between two seals with vastly different outcomes. I'm just going to order a few more Vortek seals and use those whenever necessary.
R
 
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Yeah, I’ve mainly just re-used OEM seals when I do a tune shortly after buying the gun or the green Aussie seals. I’ve haven’t seen an oversized OEM seal and Aussie seals don’t require taking off too much material (on my lathe) for a solid figment.

I just installed my first Vortek seal in a HW30S last week, we’ll see how it works as it breaks in. I didn’t reduce Its size when installed and was getting about 690/700 fps after about 50 shots with AA 7.33 pellets.

Years ago on the GTA, a member said “a good seal fit“ should require about 3lbs of pressure applied to the piston ….. to side in.

If you know what you doing, ARH seals allow a good seal fit no matter what condition you find the gun in. However, this approach usually requires more fitting time on the seal as their intentionally oversized.
 
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