GTA
PCP - HPA - C02 Gate => QB-7X Gate -W/Co2 & HPA => : wvkeith October 15, 2007, 07:51:44 AM
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I'm getting ready to add a PCP tube to my QB78 and was wondering if I need to make any changes to the valve spring or hammer spring to prevent valve lock. The rifle has had the typical mods done to improve the gas flow but the springs are stock.
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I would reckon heavier hammer spring if you plan on running pressures higher than 850 psi (co2 average at room temperature). The VERY FIRST thing I would consider besides the springs and doodads is making sure that valve stays in the tube under pressure. We talk a lot about modding these guns, and a lot about how to make them faster, stronger, better than before....but it wont matter a bit if the valve is improperly pinned into the tube and you end up wearing it inside your chest. Ok, I'm done with my soapbox! Have you asked the guy who is making you the tube what he recommends as far as springs and such? If this person is making PCP QB conversions I would guess he has already figured this stuff out. Just a thought.
Be safe,
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Yeah I knew about adding extra screws in shear to keep the internals from blowing out the rear of the rifle. I have emailed the supplier and am sure he will answer, just thought I'd ask here too. I'm pretty sure a stronger hammer spring and one of the delrin/stainless valve stems will be needed but was hoping someone with first hand experience would share their knowledge.
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Keith, Dan has a very good point here about high pressure air. I sure hope you have all the right information avaiable to you before taking on filling a tube with high pressure air. One of the GTA's major concerns about air guns is Safety. We have some excellent talent here on the GTA but not just one person knows everything. So I hope that you are getting your info in the proper order when it comes to moding a QB or any other co2 or pcp.
Gene
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I think Ian Lamb from the UK has dabbled with this in the past but I don't know if he's had sucess. Search for QBtune on Google and you should find him.
regards,
Alan
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I heard back from the guy I'm buying the tube from and he told me how to fix it.