New Qb79 ALU/DEL Valve (HPA) *UPDATE* Need help

[tronickero]

Hello

Im Tron from Chile ,Recently designed and machined a new valve for my qb79 (the factory valve was badly machined), after reading many posts (Jason, Bob and SeanMP) this was the result:

made of 7028 aluminium and delrin seat
valve throat : 0.219"
and exaust port: 0.20" (Also radiused the inside edges of the exhaust to reduce turbulence)
Poppet OD: 0.236"
transfer port: 0.17 (poly tube)
Poppet Angle 30*

670 fps with 18.13 gr (18FPE) /1000psi regulator output pressure/all other parts stock of factory







(The parts are with silicone-teflon grease so it has that look)

Sorry for my bad english

Is my first airgun mod (to be continued 30 FPE is the goal) I'm student of chemical engineering, 21 years old and I'm already on the dark side hahaha

Regards
Tron

[tronickero]

What is the best way to enlarge the barrel port ?

[nervoustrigger]

Enlarging the barrel port is easy enough to do with a hand drill.  For .22 cal, something in the vicinity of 0.160" - 0.170" is about as large as you should go to prevent pellets from getting marred as they pass over it.

You can remove the burr by quickly and easily by reaching in with a 1/8" diamond ball grinding bit loaded in a Dremel.  If you don't have access to those tools, you can get it done with wet/dry sandpaper taped or glued to a dowel or skewer.  Something like 320 grit to knock down the burr followed by 400 for smoothing.

[tronickero]

*Actualization*

My qb79 configuration

AluDel valve

Valve throat : 0.219"
Exaust port: 0.20"
Poppet OD: 0.236"
Valve stem OD: 0.117"

Barrel port: 0.165"
Transfer port: 0.16 (poly tube)
Barrel secured: M5
Reg output pressure: 1550 PSI
The nose of the bolt probe out to 0.165"

Original cock-on-close action
Hammer spring: Stock tension (No RVA)

Chrony testing:

800 fps JSB 15.9gr    22.50 FPE    GROUP: 0.45" @  45 yards
760 fps JSB 18.13gr  23.08 FPE    GROUP: 0.3"   @  45 yards

I hoped more velocity.   the goal is 30 FPE

some suggestion ?

[a1rgunz]

Your limiting factor might be the short QB79 tube, but I would try adding shims to the stock hammer spring. I modified the original valve in my QB78 to have very similar specs to your valve, and have been able to reach in the low 800s with beeman kodiak pellets. That was with three washers added to shim the stock hammer spring.

[Hobbyman2007]

The plenum is small on the qb79, you're going to need more air pressure to get to 30 fpe. I would try closer to 1400psi. Once you pin the valve and the tank block with the proper strength screws of course.

[MJP]

Not by much more pressure, I'm getting 22fpe on my .22 qb78 with 1100psi.
But I have bigger valve and ports. 6mm ports from valve to oval barrel port.
Other than that 5mm longer hammer stroke stock spring and cock on opening mod.

Marko

[Chako]

*Actualization*

My qb79 configuration

AluDel valve

Valve throat : 0.219"
Exaust port: 0.20"
Poppet OD: 0.236"
Valve stem OD: 0.117"

Barrel port: 0.165"
Transfer port: 0.16 (poly tube)
Barrel secured: M5
Reg output pressure: 1550 PSI
The nose of the bolt probe out to 0.165"

Original cock-on-close action
Hammer spring: Stock tension (No RVA)

Chrony testing:

800 fps JSB 15.9gr    22.50 FPE    GROUP: 0.45" @  45 yards
760 fps JSB 18.13gr  23.08 FPE    GROUP: 0.3"   @  45 yards

I hoped more velocity.   the goal is 30 FPE

some suggestion ?

1550psi out put and stock hammer spring?
I'm not a professional, but I'm pretty sure that all you need is a little more hammer spring...

[nervoustrigger]

I agree, need more hammer spring preload.  In stock form, it is about right for 1100 - 1200psi.  For 1550, add preload.

[tronickero]

thank you very much to all 

I have a doubt

it will be possible to increase 100 fps only adding hammer spring preload? 

Tron

[nervoustrigger]

It's very much possible.  With a 1550psi setpoint, the valve is harder to knock open so the lift and dwell may be very little.  One of my earliest experiments was a similar arrangement and the valve barely opened enough to lob the pellet across the yard.  With some preload added, it came alive.

[a1rgunz]

^^^^ What he said. I've experienced the same thing.

One thing I'm currently doing with mine is the addition a second, larger diameter spring instead of increasing preload. It is a shorter spring as well and goes between the rear of the spring guide and the hammer. I find cocking the two springs together to be more pleasant than the preloaded stock spring, while giving the same results.

[SpiralGroove]

It's very much possible.  With a 1550psi setpoint, the valve is harder to knock open so the lift and dwell may be very little.  One of my earliest experiments was a similar arrangement and the valve barely opened enough to lob the pellet across the yard.  With some preload added, it came alive.

Yes ............ unless you drastically cut your receiver (reduced plenum) you should be able 26 to 30 fpe by getting more hammer strike.
I inserted a 3/8" brass sleeve into the hammer/spring guide to get more hammer spring compression.  Also, it's very easy to add the RVA and then you can adjust velocity between 10 fpe and 30 fpe.  By adjusting velocity to be about 85/90% of maximum, the rifle will shoot most efficiently and get the most shots per fill.
Jason is the GTA's expert on these guns .