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Power Drop As Air Fill Drops

Discussion in 'Anything Airgun Related' started by Dannaz, Nov 12, 2019.

  1. Dannaz

    Dannaz Member

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    I have a fx impact mk2 the power drops at the same time as the air fill pressure drops any ideas?
     
  2. hamza

    hamza Posting Addict

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    What's your reg pressure set at?

    Presume you've confirmed this over a chrono?
     
  3. robs5230

    robs5230 леший

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    Has it been "tinkered with" ?
    if power starts to drop from full with every shot, giving a power slide, somethings amiss. Possibly even reg not working.

    Or do you mean power starts to drop with every shot from a certain pressure as it drops off reg, which could indicate everything is normal ?
     
  4. Dannaz

    Dannaz Member

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    Power is at 12fp at 250 bar and is consistent 6fps spread but as the air is used the power slowly drops I have recently had a HuMa reg fitted
     
  5. robs5230

    robs5230 леший

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    Then It looks like its been badly set up.
    I'd take it back to whoever fitted the reg and get them to sort it.

    Many think fitting a reg is easy. In some respects thats true. But its generally NOT plug and play.

    Setting it up properly is the time consuming bit
     
  6. Dannaz

    Dannaz Member

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    How would you set it up? Do you mean with valve and hammer adjustment?
     
  7. robs5230

    robs5230 леший

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    Thats what I mean.
    Give @bucketboy a message.
    He knows his onions and has recently sorted his Impact. I've never worked on one.
     
    Blackmax and Dannaz like this.
  8. Dannaz

    Dannaz Member

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    Thanks m8
     
  9. Dannaz

    Dannaz Member

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    60bar
     
  10. BallisticBill

    BallisticBill Posting Addict

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    Valve and hammer adjustment shouldn't make any difference to power profile when the cylinder is above the reg set point (but will raise/lower the power). If the reg chamber is at the same pressure irrespective of cylinder pressure then the air delivery will be constant for any particular hammer and valve spring setting. So the problem must be with the reg or reg inlet valve operation.

    All regs have a slight cylinder pressure dependency, so it's not unusual to see a slight power drift when the cylinder pressure is above reg set point. Typically, a higher cylinder pressure would give a slightly higher reg pressure. If your reg set point is well below the gun's unregulated power peak the downward drift would be more than if the reg set point was higher. If you imagine the reg set point is on the downward slope of the bell curve, a small overrun of the actual reg pressure would cause the power to increase. If the reg pressure is set at, or close to, the peak of the bell curve, any small deviation in actual reg pressure will have no significant effect on power.

    Someone might be tempted to set the reg pressure on the low side, expecting this to give more shots (from the bigger pressure difference between fill and coming off reg). This can be counter-productive because the air efficiency can decrease (a given mass of air carries less energy at lower pressure so you have to use more air for every shot to get the same power). So regs should be set close to the peak of the unregged curve.

    How much of a drop are you getting?
     
    Pete2 likes this.
  11. bucketboy

    bucketboy Keyboard Hero

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    All regs have have a slight difference in reduced pressure as the fill pressure changes because it’s harder for the reg to shut against higher fill pressure

    if you are getting maximum power at 250bar then I would guess that you are using all the air available push the pellet. As the fill pressure drops, so will the reg pressure particularly it the reg is set on the low side. The reduced reg pressure at lower fill pressure will result in lower velocity because you have used all the air reserve.

    I would up the reg pressure slightly, then reduce hammer load. Better still if you can bypass the valve bump stop, use that to fine tune the speed. There are plenty of good YouTube videos on how to balance the power on an impact.

    I have fitted one of these to my impact this evening, once I have fine tuned it, I will make an A/T to stop accidental adjustment.

    FC509190-5D75-484C-9027-7FBB1CBF5CBE.jpeg

    Bb
     
    Blackmax likes this.
  12. Dannaz

    Dannaz Member

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    Wow sounds very complicated ,much appreciated for the info and time taken ,so do you suggest I turn the reg up ? Reg is at 60 bar , air fill pressure is at 250 bar at 12fp and 150 bar 11.3fp
     
  13. BallisticBill

    BallisticBill Posting Addict

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    I don't have an Impact but 60 bar seems low. What do FX say it should be set at?

    In the absence of any specified setting I'd up the reg set point by 10bar and adjust the hammer only after you've seen what happens to the power. If the profile is okay, leave it at that, otherwise you could keep going in 5 or 10 bar increments, testing after each adjustment. You will know if you've gone too far - you will see an increase in power as the gun comes off reg.
     
    Dannaz likes this.
  14. Dannaz

    Dannaz Member

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    Fx set a sub 12fp reg at 50 bar I got a HuMa reg fitted and there reg pressure starts at 60 bar for low pressure sub 12fp
     
  15. BallisticBill

    BallisticBill Posting Addict

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    Just looked at the FX manual - doesn't make any distinction between FAC and sub-12 - but that says default is 140 bar and reg should never be set below 100bar. (It may be the FAC manual but it doesn't say so.) I would expect a Huma reg to be no lower than the original unless there are other mods to the firing valve and transfer port. You would need to open up the port to operate at lower pressure.

    The manual says you lower the reg pressure to 40-50 bar to change the bottle, then turn it up again to use the gun.

    If the gun is optimised to run at 100-140bar and you are running at 60 that would certainly explain the difference. I see the Huma Impact Mk1 reg is designed to run at 50-90 bar; they don't quote a range on the website for the Mk2. You won't do any harm turning it up to 90 and it will be obvious if you've gone too far.
     
    Last edited: Nov 13, 2019
  16. Tim_B

    Tim_B Pro Poster

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    Normally sub 12 impacts are set around 60bar from the factory - mine is.

    You can spend hours setting it up - this is half the fun. Follow the instructions given And you’ll be on the right track.

    Some FX’s benefit from higher reg pressures - my crown did. I haven’t messed with my impact as I haven’t needed to.
     
    Dannaz likes this.
  17. Dannaz

    Dannaz Member

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    I have fitted a gen 3 HuMa reg I think it's between 60-135 bar.
     
  18. MikaMutt

    MikaMutt Engaging Member

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    Dannaz likes this.
  19. Dannaz

    Dannaz Member

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  20. Dannaz

    Dannaz Member

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    The fx reg had issues it had the 1st 4/5 low fps problem if left for to long the power would be down by up to 100fps
     

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