GTA
PCP - HPA - C02 Gate => QB-7X Gate -W/Co2 & HPA => : iconoclast December 26, 2008, 02:25:55 AM
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I'm looking at the QB78 Parts Diagram and trying to understand how the QB78 works.
It's not clear to me what are the functions of the valve assembly and hammer and how they interact.
Also, I'm trying to understand the CO2 flow from the cartridges to the pellet.
Would someone be willing to explain this to me?
Thanks.
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Hmmm. Here goes it in a nut shell. CO2 in front of the valve after piercing gives high pressure CO2 on front of valve. Spring pressure in valve keeps valve closed as well as pressure from CO2. As you cock the rifle, the bolt drags the hammer back over the sear and when you close the bolt, the hammer stays back behind the sear under spring pressure. When trigger is pulled, sear drops, hammer slides forward and smacks the valve stem and quickly opens the valve (kind of bounces the valve and doesn't leave it open). CO2 escapes past the valve and through the top of the port in the valve body and is transferred through the receiver tube port through the barrel port and behind the pellet. The bolt doesn't allow the CO2 to escape 'backwards' and the pressure drives the pellet forwards. To gain more power, make the flow from the powerlet through the valve, through the transfer port more efficient. You can also increase the 'dwell' or length of time that the valve stays open by either lightening the valve spring or increasing the pressure on the hammer spring. I won't go on about mods, but efficiency is what it boils down to. Hope this helps.
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Thanks, that was really easy to follow.
I now understand why adding a spacer to the hammer spring increases the CO2 flow.
It keeps the valve assembly open longer.
However, one point still not clear is how the hammer only momentarily drives the valve stem forward.
It seems that the hammer in it's rest position would keep the valve open.
Obviously, it doesn't.
What allows the valve stem to only momentarily open as the hammer drives forward?
Does the check valve spring drive the valve stem back and the hammer back after the hammer has lost it's momentum?
Thanks for the help in my understanding.
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In the GTA Library you will find what you need..
http://www.gatewaytoairguns.com/library/Charlie’s%20QB-78%20Tune.htm
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From what I gather, the CO2 pressure helps force the valve to it's seated position. It will overcome the hammer spring, but not it's inertia.