Tuning FX Impact Mk2/M3 - slower first shot - no reg creep - quasi-scientific analysis
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So a dash size -104.
FYI the preferred convention for metric callouts is the cross-section first followed by the ID. M2.62 x 2.84
I’m still suspicious of it being an imperial size O-ring...
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I thought viton doesn't like high pressure air and can swell under high pressure correct me if I'm wrong
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Viton does indeed swell. Whether or not that characteristic will have any influence on friction I don’t know but I’m not inclined to think it would. The pressure differential will be where all the squeeze comes from.
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The stiction issue is well known with balanced valves. However, FX designed a regular valve which is affected by stiction.
More details on stiction with balanced valves: https://www.gatewaytoairguns.org/GTA/index.php?topic=149348.40
More details on stiction with balanced valves: https://www.gatewaytoairguns.org/GTA/index.php?topic=149348.40
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It can't be a normal valve it would take a lot larger hammer to produce the power impacts can make wouldn't it my raw is a normal valve and it's used a 63 gram hammer and heavy spring I don't know i could be wrong though how heavy is impact hammer
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Hmx raw has around 30cc plenum.
Impact has more than dbl that.
I ran a 100bar plenum in my mk2 impact
same pellet same speed in hmx requires 130bar plenum
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I would say Impact valve isn't that good as it suffers from stiction. It also relies on the oring static and dynamic friction. Other guns like e.g. Cricket does not suffer from that as there is no oring involved in the valve working cycle.
Impact M3 has some improvements. I wonder if the valve stiction was eliminated there. I doubt.
Impact M3 has some improvements. I wonder if the valve stiction was eliminated there. I doubt.
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I will tell you right now. My M2 and M3 are both out so I’ll head downstairs to the chronograph with the M3.
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Reg had crept up 2-3b over a couple days but I have my hammer spring set close to the knee of my reg setting so I don’t think 2-3b is a big deal. First shot 866fps. Then reg was where it should be and the second shot was 873fps. Then 881, 877, 878, 878, 880. This is with a .22 M3 Compact with a reg setting of 137b. My M2 that has a more pronounced problem with first shots is a 600mm .25 with a reg setting of 128b. It does have dual regs so that puts that part of the equation on a level playing field with my M3.
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7 feet per second isnt bad at all
Corny my raw hammer is lightened from original by like 10 or more grams and am running a external plenum so at 125 bar on the raw pushing 34 gr jsbs at 907 to 913 and using a Huma reg external plenum is 25 cc so it wouldn't be more than double the size of it I was thinking mk2 plenum my point was is 60 grams more than double the hammer weight that is in a impact so if it were a true conventional valve wouldn't it take more to open it I don't know I know it has a sticktion problem for some people and others have seemed to be able to tune it mostly our of equation 7 fps difference isn't really anything why are some having more of a problem than others I'm just curious I haven't been inside my impact and not trying to be wise ass just curious is all
Corny my raw hammer is lightened from original by like 10 or more grams and am running a external plenum so at 125 bar on the raw pushing 34 gr jsbs at 907 to 913 and using a Huma reg external plenum is 25 cc so it wouldn't be more than double the size of it I was thinking mk2 plenum my point was is 60 grams more than double the hammer weight that is in a impact so if it were a true conventional valve wouldn't it take more to open it I don't know I know it has a sticktion problem for some people and others have seemed to be able to tune it mostly our of equation 7 fps difference isn't really anything why are some having more of a problem than others I'm just curious I haven't been inside my impact and not trying to be wise ass just curious is all
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Oops 15 fps still isnt a game changer after sitting for 2 days 25 to 30 I would consider something would have to be down but how long does it take to set in I burn the first shot any way before loading and my hunting is pretty close by usually pretty fast pace to . I can see where the oring could bind more towards the cone seal it would be pinched more
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As I remember is that in 1st generation Impact, there was an X ring to act as dynamic O ring and it was placed in a groove from the outer side of the plenum.
This may be one of the reasons that 1st generation Impact had not such issues.
The X ring would continuously hold some of silicon oil and keep it as friction free as possible.
But that O ring needed to be replaced much earlier as compared to the now used PU round O ring.
Looks like FX wanted to give the users peace of mind that this O ring will not leak.
Yes it lasts much longer but perhaps at the cost of stiction.
Bhaur
This may be one of the reasons that 1st generation Impact had not such issues.
The X ring would continuously hold some of silicon oil and keep it as friction free as possible.
But that O ring needed to be replaced much earlier as compared to the now used PU round O ring.
Looks like FX wanted to give the users peace of mind that this O ring will not leak.
Yes it lasts much longer but perhaps at the cost of stiction.
Bhaur
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Why not give a quad ring a try they make small ones I don't know how hard they make them though not a bad idea I would think it would give pretty good number of shots before replacing would be needed does the mk2 use any quad rings ?
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It used to be 90 shore quad O ring. Later they replaced it with ordinary PU 90 shore O ring.
They also made this change in their part list available on their website.
So if you now check their Impact mk1 parts list you will not find this quad O ring there.
Bhaur
They also made this change in their part list available on their website.
So if you now check their Impact mk1 parts list you will not find this quad O ring there.
Bhaur
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When I picked up a bunch of orings for my impact I went off a list and wasn't sure exactly what I needed and ended up with a bag of smaller quad rings too that maybe what they were for was mk1
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This oring list was something someone else put together and was reposted and I believe mk1 and mk2 we're both in the list I'll look at the size and post it if you like I can do so tomorrow
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Hi guys,
After scratching my head even more and exploring the resources I think I managed to find the reason why FX Impact Power Plenum valve suffers from severe stiction. The answer is: there is a design flaw. Let me describe it in greater details.
Early balance valves were suffering from severe stiction issues. Bob Sterne from GTA forum managed to identify the problem. Please familiarize with the following post by him:
The direction of valve movement exaggerates the stiction issue be wedging the oring even deeper between the valve rod and plenum. Please take a look at PUR90 oring which I removed from my plenum.
It is obvious there was wedging involved. The first shot after sitting for a while suffers from the stiction because the rod movement makes the wedging even worse. Then, when the valve closes it removes the lip of the oring from the gap.
The conical cavity which I presented you is not that deep. It is shallow enough for the oring to fill it entirely.
The conclusion is FX Impact Power Plenum valve has a design flaw promoting stiction issue.
After scratching my head even more and exploring the resources I think I managed to find the reason why FX Impact Power Plenum valve suffers from severe stiction. The answer is: there is a design flaw. Let me describe it in greater details.
Early balance valves were suffering from severe stiction issues. Bob Sterne from GTA forum managed to identify the problem. Please familiarize with the following post by him:
The direction of valve movement exaggerates the stiction issue be wedging the oring even deeper between the valve rod and plenum. Please take a look at PUR90 oring which I removed from my plenum.
It is obvious there was wedging involved. The first shot after sitting for a while suffers from the stiction because the rod movement makes the wedging even worse. Then, when the valve closes it removes the lip of the oring from the gap.
The conical cavity which I presented you is not that deep. It is shallow enough for the oring to fill it entirely.
The conclusion is FX Impact Power Plenum valve has a design flaw promoting stiction issue.
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