 |  | | | |  | |  |  | 1322/1377 Pumping problems! |  | |  |  | |
 Posted: Mon Mar 23, 2009 6:36 am |
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| AirGunEric |
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Anyone have any ideas what would stop a pumper from accepting pumps?
I don't have the gun to look over, but the issue is that after 10 pumps it appears no more air can be pumped into the chamber. Overall velocity is down as well as compared to previously.
Would a blown pump cup, or crap build-up somewhere cause this? |
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| Posted: Mon Mar 23, 2009 10:16 am |
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| DerekVinyard |
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The valve retains it's internal pressure via the exhaust valve seal, the o-ring between the valve front/rear halves and the front check valve. If the valve retains pressure over time, then they are not suspect.
The pump cup and the o-ring on the outside of the valve front create your pump seal. If the either one is not doing it's job, your pressure generated will decrease anywhere from marginally to majorly. If the pump cup is worn, a couple drops of oil will usually improve it for a few strokes. A really bad pump cup will also allow the forearm to drop due to gravity as there is no vacuum to hold it.
It's easier to diagnose when you have the airgun in your hands... |
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| Posted: Mon Mar 23, 2009 10:59 am |
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| AirGunEric |
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| After getting more of the story, it appears as though additional modifications done to the valve (stem mods and lighter spring installation) on a unit with an FTP kit installed may be allowing the valve to bleed out due to a lack of spring tension to hold the valve in place beyond a specific pressure. Probably more the re-shaped valve head than anything, but I think it may be a significant contributor to the issue beyond any seal problems... |
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| Posted: Mon Mar 23, 2009 11:18 am |
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| rsterne |
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Yeah, my guess would be either an internal valve sealing issue.... or a damaged O-ring on the F-T-P or valve due to being re-assembled without de-burring the inside of the pump tube.... Many times driving the pump pivot pin out leaves quite a burr there.... I have also seen seal-slicers on the inside of the slot in a new gun.... 
Like DerekVinyard says.... if the valve will retain air for an hour without bleeding out.... then my guess is it's the piston or valve external O-ring.... or both.... 
Bob |
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_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| | | | | | | | | 1322/1377 Pumping problems! | | | | | |
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