Tuning Power Plenum a NoGo (Taipan Veteran)

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Dave

Dave

Member
Jun 20, 2015
416
11
Ohio, United States
Installed the Power plenum on my Taipan last night, and found that the gun would not refill with air. After trying for a little while it even stopped taking air into the fill valve. It took me awhile to figure it out last night, but was able to get check valve unstuck, but still not filling with air.

Today I called Utah airguns and talked to them about filling issues. Travis confirmed the one issue was check valve related. However, he mentioned that the power plenum was designed for FX guns and not really suited for the Taipan. With this in mind, I took everything back apart and removed the power plenum. During removal, I noticed that the o-ring to air tube seal, as well as the seal to the dun seemed less snug than the normal air tube to gun seal.

Since I was already into the gun, I pulled out the standoff for the stock reg and saw that it is shorter than the one that comes with the huma reg. Nowing that the Huma I purchased is set slightly higher that stock, and the slight increase in plenum space, I went ahead and installed the Huma.

Now that everything was back together, it was now the moment of truth. After a little pumping, the pressure started to rise in the tube and pump gages.Yes, I am hand pumping from empty! I was planning on purchase of a tank and compressor, but car repair depleted my funding, so it will be awhile till I get a setup.

I would like to hear from others that installed the Power plenum on whether they had any Issues, or something I could have done differently to make it work.
 
I checked my order and it was for the Taipan power plenum. Everything when together as expected, bug it doesn't seem like it sealed tight. 

20210727_181743.1627424440.jpg

 
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I bought a boxed o-ring assortment last year. I replaced my Marauder breech o-ring with the same nominal size and it was way too loose. After checking the SAE o-ring standards and several of the ones in the box I found a couple of sizes were manufactured to nominal size, not specified size, the 1/16” cross-section was .0625, not the .070 specified. A trip to NAPA with calipers produced the correct o-ring. I never checked the rest of the box but I haven’t used another ring from it.
 
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When I put the extra plenum on my Vet, I had to use a different oring. Can’t remember the size. I dug it out of my collection of metric orings. The one that came with my plenum was a no go. Like Motorhead, when I looked at it, I knew there was no need to even try it. Sadly with my Vet standard .22, the plenum project was a waste of time. My barrel is too short to see the benefits of it. The good news is Taipan got the plenum size right when they made the .22 standard.
 
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I left it at 200 bar over night and pressure held. I brought it up to 250 bar this morning, and will let it set all day. 

Tonight I will start testing with the stock spring, as 900 FPS is all I need for the 34gr JSBs. I will set some money aside for a slug barrel, and make the purchase once they become available. I the first 6 NSA slug weights to get started with, as that was my original plan for this gun, and pellets were not available other than H&N Barracudas at the time I got the gun. Fortunately, I had one tin of the 34s that I purchased at the PA cup in 2019, that have gotten me through for now. I did just order 2 Tins from TT, which was a little high priced, as tonight's testing will eat up most of what I have left.
 
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Would agree looking at Pic, cross section diameter of O-ring looks too small .... that or the o-rings groove is correct width but cut too deep ?
Click to expand...

From your description it seems you are referring to the 2nd pic posted, right? That is the one that is sealing. It's the one with the o-ring that looks blown out of the groove that is leaking.
 
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I just battled this on a wildcat. No matter what size o ring in thickness I used on the Huma reg, air from the high pressure side would push past the first o ring on the reg and out the air tube’s vent hole as the tiny bubbles would show from my leak detector. 

Best thing to do is clean off the air tube of all lubes with acetone. From there I rigged up 1000 grit wet/dry sandpaper onto a piece of 3/4” PVC, and lightly sanded the area that the regulator would sit in. 

Another wipe down with acetone, and after re installation of parts, no leaks. The scuffing that the sandapaper gave was an area for the o ring to bite down into. Like crosshatching for a piston in automotive.
 
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It looks like everything sealed well this time around. I set to 250 bar this morning and left it all day. When I got home after work the pressure was exactly where it was before. 

I did a little initial testing to see how the mods changed things. First I ran 2 each of 36.2 and 38.9 grain NSA slugs at full hammer spring setting, which showed speed consistent with 61 ft-lbs energy. This didn't surprise me, as both choke and breach of barrel seem really tight in the Taipan. The probe actually indents the 26 FX hybrid slugs during chambering. 

20210728_203028.1627518669.jpg


Then I ran 34gran JSBs through at max and saw 930 FPS, for 65 ft-lbs. I actually had to lower spring pressure a huge amount to see the velocity start to drop, so I believe that this is the max speed this barrel will allow for that pellet, with a bunch of wasted air, or the hammer needs more weight to let enough air in the increase above this velocity. I suspect the first is correct, as I put stock spring in and adjusted for 900 FPS, I noticed a big difference in sound level, which I think was the wasted air at the higher velocity. 

I got 20 shots from 250 down to 155 bar by gage on rifle, with reg set at 143bar. I think I should get more now after reducing velocity for peak accuracy. Now I am able to run the stock spring at a reduced force on the hammer to provide sufficient air for the 34s. Once the longer slug barrel becomes available, I will put that on and see what she is able to push.

What surprised me the most is that after total disassembly and putting it back together, my zero was still nearly perfect to prior setting.
 
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I'm not doubting the wisdom of this mod, but, for my education, what is the net gain from this installation?
Click to expand...

The mod increases plenum volume and allows reduced hammer spring pre-load for the velocity. I am sufficiently less than maxed out with stock spring now, while before it was completely maxed. 

Also this will give me the extra air needed once I go to a slug barrel for long range use, which was my intention from the beginning. However, barrels are not available at the moment, or I would have purchased and changed that out first. 


 
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I'm not doubting the wisdom of this mod, but, for my education, what is the net gain from this installation?
Click to expand...

The mod increases plenum volume and allows reduced hammer spring pre-load for the velocity. I am sufficiently less than maxed out with stock spring now, while before it was completely maxed. 

Also this will give me the extra air needed once I go to a slug barrel for long range use, which was my intention from the beginning. However, barrels are not available at the moment, or I would have purchased and changed that out first. 

Click to expand...

THanks Dave, that's basically what I assumed. I have a Veteran standard .22 and like it a lot. I shoot the 18 gr at 890 or so. It shoots great, no interest in slugs.or more power.
 
Upvote 0
I'm not doubting the wisdom of this mod, but, for my education, what is the net gain from this installation?
Click to expand...

The mod increases plenum volume and allows reduced hammer spring pre-load for the velocity. I am sufficiently less than maxed out with stock spring now, while before it was completely maxed. 

Also this will give me the extra air needed once I go to a slug barrel for long range use, which was my intention from the beginning. However, barrels are not available at the moment, or I would have purchased and changed that out first. 

Click to expand...

THanks Dave, that's basically what I assumed. I have a Veteran standard .22 and like it a lot. I shoot the 18 gr at 890 or so. It shoots great, no interest in slugs.or more power.
Click to expand...

I almost forgot, If one desires highers shot count, the increased plenum space allows lowering regulator setting to still produce the same velocity as the smaller plenum, but you can shoot it down to lower pressure before falling of reg. 

However, someone else will have to give you data of reg setting and shot count increase. 
 
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