About to take the plunge .... QB-79 on HPA question ?

[rsterne]

But considering that air pressure increases less drastically than co2 with temperature increase, a good argument can be made that an 850psi HPA tank is LESS likely to cause a problem than a co2 tank.  IF both exposed to 98F (which is not a terribly unusual temperature), which would stress the tank block mounting system more?

Air pressure increases with the ABSOLUTE (*R) temperature (*R = *F + 460), ie very slowly.... If you start with 850 psi at 70*F (530*R), at 100*F (560*R) the pressure will only increase to 850x560/530 = 898 psi.... CO2, which starts at 850 psi at 70*F is up to 1400 psi at 100*F (when the gun is full).... What started out at the same pressure is now a 500 psi difference.... In addition, once you make the shot, the next shot will be back down to 850 psi because of the regulator.... No question that 850 psi air is less stressful to the tank block mounting system than CO2.... at 100*F, so is 1400 psi HPA, because at 110*F, the CO2 is once again at a higher pressure.... Here is the pressure chart for CO2....

Know of no tests made of the real strength of QB tubes.  Suspect that the type of steel and heat treatment has varied over the years.

I agree, that's why I used mild steel (no heat treating) in my calculations and still got a safety margin of 3.9:1 at 1800 psi.... With any safety margin over 2.2:1 fatigue is not a factor for steel.... All I'm really trying to say here is that if QBs don't explode when left filled with CO2 in a hot car.... or laying out in the Texas sun at 120*F.... then I can't see why there should be any more problem with any HPA setup providing it is equipped with a 1.8K burst disc.... In order not to blow the burst disc that places an absoulte limit on the regulator pressure of 1500-1600 psi.... IMO, using 1400 psi will be no harder on the gun or more dangerous than using CO2 on a 100*F day.... 

Bob

[Motorhead]

IMO, using 1400 psi will be no harder on the gun or more dangerous than using CO2 on a 100*F day....  

Bob

So ... optimal internal working pressure and guns performance with a margin on safety, would it be a safe bet that @ 1200# regulation on HPA would be very near a sweet spot that would allow all the valve and flow tricks to work in harmony ?

[rsterne]

There is one other consideration with using a QB on HPA.... and that is what the hammer spring can dump.... I did quite a bit of experimenting with a QB 78, with the following results....



Note that I was just filling the tube only, and shooting the gun as a non-regulated PCP.... The "stock" curves were with just the bolt probe cleaned up to 5/32" ID.... The "ported" curves were with the filters in the valve removed, and a poly transfer port (0.161" ID).... The "modded" curves were for a completely modified valve.... no piercing pin, slotted body, beveled poppet, new spring & seats, 0.218" throat, ports streamlined.... The "spring" curves were with the hammer spring shimmed about 3/16".... Here are the important things to note....

With a stock gun.... the peak velocity was reached at 1200 psi.... with very little change from 1000-1300....
With the filters removed and a poly port mod.... the peak velocity was reached at 1100 psi.... with very little change from 900-1200....
With full house mods on the valve.... the peak velocity was reached at 1100 psi.... with very little change from 1000-1200....
In order to utilize more than about 1200 psi.... you need to shim the hammer spring.... With 3 washers, it peaks at ~1800 psi.... with 2 ~1600 psi.... and with 1 ~1400 psi....

In conclusion, 1200 psi would appear to be the best pressure for performance on HPA unless you shim the hammer spring.... It will allow a wide variety in the state of tune while supplying the best velocity with a stock spring preload.... For maximum performance, 1 or 2 washers (1/16" thick) under the hammer spring will allow the use of higher regulator pressures.... More than that is not required because of the requirement for a 1.8K burst disc for safety.... Using a stronger hammer spring preload than is required for the pressure being used will result in wasting air with no increase in power....

Bob

[Motorhead]

Bob,
Thanks for the VERY informative postings !!
Took us a bit to actually say in Blank & White terms what I was after in my inquire, but we got there easy enough tho 
Will get the 13ci HPA tank with a 1200# Regulator and start the mod process after Christmas.

Thank you again !!

Regards,
Scott

There is one other consideration with using a QB on HPA.... and that is what the hammer spring can dump.... I did quite a bit of experimenting with a QB 78, with the following results....



Note that I was just filling the tube only, and shooting the gun as a non-regulated PCP.... The "stock" curves were with just the bolt probe cleaned up to 5/32" ID.... The "ported" curves were with the filters in the valve removed, and a poly transfer port (0.161" ID).... The "modded" curves were for a completely modified valve.... no piercing pin, slotted body, beveled poppet, new spring & seats, 0.218" throat, ports streamlined.... The "spring" curves were with the hammer spring shimmed about 3/16".... Here are the important things to note....

With a stock gun.... the peak velocity was reached at 1200 psi.... with very little change from 1000-1300....
With the filters removed and a poly port mod.... the peak velocity was reached at 1100 psi.... with very little change from 900-1200....
With full house mods on the valve.... the peak velocity was reached at 1100 psi.... with very little change from 1000-1200....
In order to utilize more than about 1200 psi.... you need to shim the hammer spring.... With 3 washers, it peaks at ~1800 psi.... with 2 ~1600 psi.... and with 1 ~1400 psi....

In conclusion, 1200 psi would appear to be the best pressure for performance on HPA unless you shim the hammer spring.... It will allow a wide variety in the state of tune while supplying the best velocity with a stock spring preload.... For maximum performance, 1 or 2 washers (1/16" thick) under the hammer spring will allow the use of higher regulator pressures.... More than that is not required because of the requirement for a 1.8K burst disc for safety.... Using a stronger hammer spring preload than is required for the pressure being used will result in wasting air with no increase in power....

Bob

[Ribbonstone]

I'd guess that 1200psi would be a good spot for the happy working of a QB with out having to do a major remodeling.I would say it is "safe" in that the tube (no more likely to have a problem than hot weather co2..which is not to say there can't be a problem...but the problem would have also happened with co2),

I USE to recommend changing the valve stem for a Delrin one right off the bat, and I have had some of the standard ones give up pretty quickly.  But on one of mine that has been in service for well over a year, I used an issue valve stem...and I'm still waiting for it to &^^& out.   Evidently, swapping out the valve stem for a tougher one isn't something you HAVE to do right away (but I still suspect you will blow that seal sooner).

Would at least take out the valve's fiber filter.

[Motorhead]

Being a 30+ year now retired small engine mechanic and still part time machinist, no such thing as STOCK 
The Qb's getting a reworking tip too tail with all potential mods looked at ....

I'd guess that 1200psi would be a good spot for the happy working of a QB with out having to do a major remodeling.I would say it is "safe" in that the tube (no more likely to have a problem than hot weather co2..which is not to say there can't be a problem...but the problem would have also happened with co2),

I USE to recommend changing the valve stem for a Delrin one right off the bat, and I have had some of the standard ones give up pretty quickly.  But on one of mine that has been in service for well over a year, I used an issue valve stem...and I'm still waiting for it to &^^& out.   Evidently, swapping out the valve stem for a tougher one isn't something you HAVE to do right away (but I still suspect you will blow that seal sooner).

Would at least take out the valve's fiber filter.

[rsterne]

I still have the stock valve seal in my 1500 psi QB 78.... but it's sure got an awful big groove in it.... I imagine a Delrin seal is in store fairly soon.... 

Bob

[Lastmanout]

 I have a couple QB79's. Nothing fancy= just screwed a tank on. One is a Ninja at 850 and one is at 1200 psi. I get a lot more shots at 850. No problems after 3 years and approx 2000 shots. Both 177 caliber. All stock they are not a real powerhouse in 177, great plinkers. I use a Mrod for huniting.

[rsterne]

No question that the shot count is dramatically affected by the regulator pressure.... Basically, if the gun is setup to be reasonably efficient, the amount of air used should be proportional to the total FPE in the shot string.... If the efficiency was a constant, there would be no difference in the air consumed between a gun that shoots 100 shots at 10 FPE and 50 shots at 20 FPE.... In practice, however, more power is often associated with lower efficiency.... which further swings the shot count in favour of lower power.... When you start trying to get REALLY big power from a gun, the efficiency, and the shot count, tend to go south in a hurry.... At some point, the valve will still be open after "Elvis has left the building" and all further increases in valve opening will do is waste air and add muzzle blast.... with no additional velocity gains....

Bob

[TimmyMac1]

I have 1200 PSI Ninja 13 CI Tanks in Stock. Any of the Ninja tanks running more than a 850 psi output all use 3K burst disks for the downstream burst protection. No reason you couldn't change it to a 1.8 but they claim it can still blow (the 1200 & 1400 PSI) disk if it gets worked enuf times. That surprised me but that is what Ninja Says.
I use a 14090 on my US FT. Works geat.

[rsterne]

I've run 1600 psi with a 1.8K burst disc but that's really pushing it as the discs are plus/minus 10%.... ie they could blow as low as 1620 psi.... I guess if it works once, it will work until/unless it fatigues and fails....

Bob

[Ribbonstone]

Think they do fatigue, which will let them fail at under their designed pressure.  The heart of a burst disk is a thin sheet of metal (and from color, it has a coper/brass base).  Each time the regulator cycles, the disk is flexed (decrease pressure...increase pressure) 

Takes a lot of cycles, but be it a coat hanger being bent, or a B52 wing strut, sooner or later it will crak and fail.

[Motorhead]

In years of Paintball play using Co2, indeed they do fail from fatigue.  Our semi auto markers running unregulated much harder on them than those regulated.

Think they do fatigue, which will let them fail at under their designed pressure.  The heart of a burst disk is a thin sheet of metal (and from color, it has a coper/brass base).  Each time the regulator cycles, the disk is flexed (decrease pressure...increase pressure) 

Takes a lot of cycles, but be it a coat hanger being bent, or a B52 wing strut, sooner or later it will crak and fail.

[rsterne]

I would think extra volume in the plenum between the regulator and the valve would help their life.... The pressure variation is much less than with, for example, a QB 79 with the regulator mount right up against the valve.... As an example, I've had a pressure gauge mounted on a QB 79 tank block fail in just a few shots from the vibration due to the huge pressure fluctuation during a shot.... Same setup with 20cc of plenum, the gauge barely wiggles and stands up basically forever.... I'm betting the burst disc will act in a similar fashion....

I've had some 1.8Ks on guns regulated at 1500-1600 and no failures after 1000s of shots.... so if one goes eventually it's a lot cheaper than a main spring on a springer, I reckon.... and a lot easier to replace....

Bob