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Non-PAL QB 79 on HPA

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rsterne:
I installed the .22 cal barrel and bolt, and the initial testing with stock regulator pressure (~850 psi) was just under 550 fps with 14.3 gr. JSB Express pellets.... I shot it down until the velocity dropped below 500 fps, and the pressure was about 650 psi, so that was my goal.... OK, so now it's time to reduce the regulator pressure to get the velocity under 500 fps.... I removed the barrel and unscrewed the tank.... You can do that with the tank under pressure provided the regulator output is under about 1000 psi, over that I wouldn't recommend it.... There is a vent hole in the tank block and just after it is unscrewed far enough to seat the check valve, the O-ring uncovers the hole and the air in the gun (but not the air in the tank) vents.... If you're not expecting it, it will scare the heck out of you.... Just go slow, and when it starts to vent wait until it quits then unscrew it another 1/4 turn and make sure it's completely vented before you take the tank off completely.... Alternately, you can shoot the gun down to zero, and if you don't have a way to dump the remaining air in the tank you will have to do that, as the tank must be completely empty before you can take apart the regulator....

The Ninja tank comes with an allen wrench to undo the setscrews in the "bonnet" and a long screw of the same thread to use as a handle to loosen the bonnet.... Remove the setscrews completely, screw in the long screw until it stops, back it out 1/4 turn so the tip doesn't drag on the regulator body and then unscrew the bonnet 1/4 turn ONLY.... Remove the long screw and continue to unscrew the bonnet by hand.... If it won't turn easily, there is probably still some air in the tank, and you MUST dump that air before proceeding.... The reason for removing the long screw is that if it is sticking through the bonnet it will hit the threads on the aluminum regulator body and ruin them, making removing the bonnet difficult if not impossible.... I speak from experience.... 

Once the bonnet is removed, you will find the following parts inside....



Left to right: the tank and regulator body.... two silver shims (0.005").... two red shims (0.021").... piston and spring.... pin valve.... bonnet.... Also shown are the allen key, long screw for leverage, and the two setscrews that hold the bonnet in place.... Inside the piston there is also a small spring for the pin valve.... It’s not in the photo, but be careful not to lose it....

There will be two red shims, but the number of the thinner silver shims may vary as they are used to "fine tune" the regulator to ~850 psi.... I have done a bit of playing with these regulators in the past, so I guessed that removing one of each thickness shim would be close to what I wanted.... I reassembled the regulator with only one silver and one red shim, filled the tank to 1000 psi and checked the output.... It was ~670 psi, pretty close to what I wanted, so I reassembled the gun and checked the velocity.... The first shots over the Chrony were 484-494 fps, averaging 490, but that was only with a 1000 psi fill.... It is common for the regulator output pressure to creep upwards very slightly as the tank is filled more, so I filled the tank in 500 psi increments with the following results:

1000 psi down to 500: 32 shots, averaging 490 fps, 484-494
1500 psi fill, 10 shots, 497 fps avg., 489-500
2000 psi fill, 10 shots, 500 fps avg., 496-504
2500 psi fill, 10 shots, 501 fps avg., 496-504
3000 psi fill, 10 shots, 504 fps avg., 497-508

The velocity was just a little too high, so I drained the tank, took the regulator apart again and removed the second silver (0.005") shim.... That dropped the pressure to ~635 psi.... Of course that was too much, and with a 3000 psi fill, 10 shots averaged 487 fps, ranging from 480-492.... I took the regulator apart yet again, and added a 0.002" shim and ended up with 650 psi.... About now I was wishing I had trusted my original plan.... I refilled the tank to 2950 psi (all the air I had) and shot two 32 shot strings.... The first averaged 491 fps (487-495) and the second averaged 489 fps (485-492).... The pressure at the end was 2000 psi, so I used 950 psi for 64 shots averaging 490 fps which is 7.63 FPE for a total of 488 FPE.... The air used was 950 / 14.5 = 65.5 bar x 13 CI = 852 CI.... The efficiency worked out to 488 / 852 = 0.57 FPE/CI which is pretty low.... However, even with that, I should be able to get about 160 shots per fill.... I didn't check the total number of shots, or the velocity at the 650 psi regulator setpoint.... but I would expect the velocity to be about 480 fps at the end of the string....

This particular regulator takes about a 0.001” shim change to change the output pressure by roughly 7 psi.... That in turn, changes the velocity by about 3 fps.... Another regulator and a different gun might not react in quite the same way.... so if you decide to follow my lead and build a non-PAL QB 79 on HPA be prepared to play with the output pressure to keep the gun under 500 fps.... Having said that, in .22 cal, you could probably remove one red shim from the regulator before initial assembly.... and then fine tune after that if necessary....

I looked at the pressure curve for this regulator, and it looks like the minimum pressure I can achieve is about 500 psi or a bit less.... I can't get to the roughly 350 psi needed to keep the .177 version under 500 fps without making other changes, so at the moment I don't plan to pursue a non-PAL in .177.... I have been thinking about the rather low efficiency, and it kind of fits with the fact that higher pressures tend to lead to higher efficiencies.... The QBs have a very strong hammer spring, and I'm wondering if that, in combination with the low pressure, is lowering the efficiency.... It is possible that running a higher regulator pressure and a lighter hammer spring might result in an increased shot count.... On the other hand, it might just mean the same shot count but less air used.... or it might not be any better.... In any case, I think this project has come to a successful conclusion.... I have made possible a non-PAL QB 79 in .22 cal, running on HPA, that will deliver about 160 shots per fill.... All in all, I think that's a success....

Bob

renowntwo:
great work.

redone1992:
Very nice post.
I have a qb 79 i have been play with it is a 177.
I m on hold on it for now waiting for a new regulator under warranty.
It leaks internally the pressure creeps up to tank pressure after a bout 2 hrs.
The first time the burst disk blew it was in the corner in the shop i was at the bench working i a bout jumped thru the roof! 

rsterne:
You can purchase a rebuild kit from Ninja that consists of a Piston, O-rings, new screws, a burst disc, and some shims.... I think they are about $15, and that, plus some Silicone O-ring lube and the photo above should allow a DIY rebuild....

Bob

lloyd-ss:
Bob,
Just noticed this thread.  I have always heard a lot about the QB's but have zero experience with them, so thanks for the learning opportunity.  I can tell I'll have to read thru this several times to pick up all the detail you have presented.
Thanks for sharing this with us.
Lloyd

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