DFG Canadian Airguns

ExoticWoody · Posted: Sun Jun 08, 2008 10:07 pm Post subject:

Funny thing, when the bottle emptied it wasn't on full throttle, which meant it was being regulated as it emptied ... Confused

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Keyrigger · Posted: Sun Jun 08, 2008 11:11 pm Post subject:

To let everyone know what the extent of the "Injuries" were, I sustained a small cut and a very sore thumb from being hit with the stock securing stud. It did take quite a few minutes for the adrenalin to work its way out of our systems as both of us were completely taken by surprise. How EW describes the tank as spinning, does show that at the time the pressure had separated the tank, regulator, and front tube block, the pressure was being reduced as it left the tank. Prior to that, the regulator was under so much pressure (2600 psi, to be exact) that it could not be spun out to vent the tank via the hole in the block.

This did show us that the block securing system is NOT up to the task of holding up to 3000 PSI and the stretched holes in the front of the tube prove it. The heads of the two screws were sheared off and that is why the two halves of the assembly parted company with such a bang. It was rather lucky that the tube was pointed straight up in the air as the screwdriver that was being tapped to vent the valve and the valve hammer left with the tube and the screwdriver was found on a table 5 feet from where it was being used.

At this junction in time, I would not trust the two Phillips head screws that hold the QB 79 front housing in place on the tube. The thread size is 4 mm and both of them should be replaced with grade 5 or better capscrews and only used with Co2, not with regulated air or unregulated air over 1250 psi. The system cannot hold back over 2000 psi for extended periods of time, and this was 3000and has been acting on the system for about 12 hours. Take this warning seriously.
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Scruffie · Posted: Mon Jun 09, 2008 1:34 pm Post subject:

Very glad that no one was seriously injured. Cool

So to use a couple of cliches. Is it live and learn & back to the drawing board?? Seems like a heck of a great system if it could be made too work safely
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DoctorFrankengun · Posted: Mon Jun 09, 2008 6:43 pm Post subject:

ExoticWoody · Posted: Mon Jun 09, 2008 7:12 pm Post subject:

Keyrigger · Posted: Mon Jun 09, 2008 8:11 pm Post subject:

That is the real sad part of this particular rifle. The results were so good, it was really tough to see that there was the potential for a catastrophic system failure. As I pointed out to EW over the phone, the work that was going on at the exact time of the screw failure only made the failure happen sooner, and as it happened, in a much safer direction than only a few minutes before. Screws that are so easily stripped, when you are taking a rifle apart and putting it back together on a regular basis, should be discarded and replaced with those that are of high quality and known pedigree. A trip to any fastener supplier, that carries metric machine screws, should give you a little piece of mind and long lasting hardware. I bought lots for my European rifles, and I have never regretted spending the coin for them. Hope this helps.
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windbag · Joined: 09 Jun 2008 Posts: 71 : Items

DoctorFrankengun · Posted: Mon Jun 09, 2008 9:55 pm Post subject:

Keyrigger · Posted: Mon Jun 09, 2008 10:25 pm Post subject:

Windbag:

Funny you should mention your 850. Both of us had thoughts that immediately went to those that have converted their 850's to HPA using the identical system that EW had on his. The failure of the regulator would result in an identical senario of the pressure locking up the valve. After the two of us had a hard look at all the individual components, we really found out that the way we should have removed the pressure, was to spin the bottle off of the regulator. Sounds hard to imagine that it would be the best way, but the design of the vented threaded section that goes into the bottle, seems to leave a longer section of material holding the bottle, then when you spin the regulator and bottle off of the rifle to bring the vent hole in the rifle's transfer block into play. Hindsight is 20/20, of that there is no question. The one possitive thing that we came out of this learing, is that there is no replacement for buying the best equipment out there, not the most handy, or popular.

With these rifles, the best system would be an 1800 psi blow out disk on the low pressure side of the regulator. If the regulator fails, the disk will let go and you will not have full tank pressure on the low side of the system. The hardest part is getting reliable disks to use, as these systems can be had from many suppliers. I know of one rifle that has this system in place, after a fashion. There are two gauges on the regulator (one on the high side, one on the low side), one fill fitting, and one 2000 PSI blowout disk. The system that was in this rifle, had all normal fittings on the high side, but none on the low side that worked. I do believe that the regulator was fitted with a low pressure side vent disk and THAT failed as well as the regulator.

Essentially, what we want is a fail-safe method of taking pressure off of the supply tank that can be called into play if the main systems fail. That will allow us to take the pressure off of either side of the system, but in a much more planned manor. Venting the tank of a rifle like a Daystate Harrier (BAM 50/51) will still be done in the same manor that was used to vent the tank on this rifle. The difference is that the Daystate cannot have the result happen to it, that this QB did. I can admit that I was not prepared for what happened and am fortunate that the biggest injury was to my confidence in how I had approached repairs on PCP systems in the past. Talk to you soon.
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ExoticWoody · Posted: Thu Jul 31, 2008 7:34 am Post subject:

Custom main tube by DFG.... Twisted Evil

Bottom view

Top view

Main tube next to original QB main tube

Custom valve build by DFG including new valve stem seal

Custom main tube internal safety by DFG

EW added stainless hex screws to adapter and main tube + 2 extra head in shear on the advice of Keyrigger

Low side gauge added by EW ... Internal burst disc on opposite side of gauge within the main tube

Air gun completely resealed using 70 and 90 Duro seals and all screws replaced with grade 5 hex or stainless including breech screw and valve hold screw....
Now this goody will need a new custom stock...LOL... Wink

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