Reg pressure inconsistent.

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ImpactX

ImpactX

Member
May 4, 2019
636
18
Minnesota, United States
Anyone else having this issues or maybe just my gun. It's the fx impact with wika gauges and huma gen 3 regulator installed. I set my reg pressure to 140 bar. When I fill my gun to 250 bar, the reg pressure jumps to 150 bar. If I shoot it 2-3 times, the reg pressure will go down to 145 bar. It will stay there until the bottle pressure gets lower. Then it will started declining even though the bottle pressure is still over 150 bar.

Example. Reg pressure set to 140 bar. Fill gun to 250 bar, reg climbs to 150 bar. Shoot 2-3 shots, reg drop to 145 bar. Shoot till bottle pressure is 200 bar, reg is at 140. Bottle pressure at 180 bar, reg pressure is then at 135 bar. Bottle pressure at 140 bar, reg pressure is then at 130 bar.

So my question is, why does the reg pressure go over my set pressure when filling the gun. 2nd question is, why is my reg pressure declining when the bottle pressure gets lower, but still above the set reg pressure. From my understanding is, the reg pressure should always be at the set pressure aka 140 bar on my gun while the bottle pressure is above 140 bar. Once the bottle pressure is lower than the reg pressure then it starts to decline. But on my gun, reg pressure deline as bottle pressure decline even though bottle pressure is still over my 140 bar I set it. Is this normal? Or maybe these wika guage from huma air isnt as accurate as ppl claim them to be? I think I spent like $90 on both wika guage and like $120 the huma reg.
 
Try not looking at those manometers and go shoot in fact put some painters tape over them just shoot for groups. Any accurate? Yo!
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My range is my backyard and its 30 yards max. So at that distance it doesnt tell me much since its leaf clover or hole on hole. I needed to test out to 100 yard but havent got time to go out plus they charge $25 to shoot there. And it's for firearm so really loud with those firearms few feet from ya. I did shoot over a chrony and results vary between 930 to 970 fps with 34gr jsb mk2. That is from 250 bars to 140 bar on bottle gauge. But on reg guage that is 150 bar to 130 bar.
 
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How many total shots have you taken since installing that HUMA? I always thought the max sweet spot for a NON POWER PLENUM IMPACT was around 130BAR? Assuming yours does not have a power plenum. Yo!
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That truly depends on caliber/barrel length. A 500 mm barrel should have higher optimal pressure for a particular energy level than a 700mm. Pre plenum and pre-upgraded valve seats these fx's commonly needed 140-150+ bar to make any considerable power...their 700mm barrels were a bandaid for awhile for smaller calibers, but ultimately for .25 cal and above to make real power they had to redo the valve seats to allow larger ports, and increase plenum volume.
 
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Try not looking at those manometers and go shoot in fact put some painters tape over them just shoot for groups. Any accurate? Yo!
Click to expand...

My range is my backyard and its 30 yards max. So at that distance it doesnt tell me much since its leaf clover or hole on hole. I needed to test out to 100 yard but havent got time to go out plus they charge $25 to shoot there. And it's for firearm so really loud with those firearms few feet from ya. I did shoot over a chrony and results vary between 930 to 970 fps with 34gr jsb mk2. That is from 250 bars to 140 bar on bottle gauge. But on reg guage that is 150 bar to 130 bar.
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I wish I could draw you an animated illustration, its quite simple but as pressure differential increases so does the amount of creep in a rifle exhibiting a lot of creep...you need to resurface either the seat or piston (I would ask someone who has experience with humas, or ask huma for a new delrin seat after explaining your situation)
 
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Not really experiencing any major swings with my AMP regulator. My reg is set to 150 bar. On a 250 bar fill it will climb to 152-153 bar, hard to tell, but just a slight increase. After a shot or two it will hold at 150 bar until the tank hits 150 bar.

That said, I have dealt with Huma regs and have rebuilt them with the kits a few times. My experience is that the Huma does take quite a number of shots to settle in to the set point running much higher than the set point starting out. I am not sure about yours dropping lower before the tank reaches the set point. That doesn't sound right at all. If it were mine I would be getting a rebuild kit and rebuilding it after say 50 shots or so if it didn't settle down.
 
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Just realized something. HUMA MAKES 2 DIFFERENT REGS for the IMPACT one is a standard and another's HIGH POWER. Which one do you have? Yo!
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My impact was the impact X mk1. But I did install the power plenum. And have 600mm slug liner. To achieve 950 fps, I have to set my reg pressure to 140 bar as for the Huma regulator, it's the standard gen3. I still have the amp reg that came with my gun. Maybe I can put that one back and see if it makes any difference. 
 
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Ackuric is spot on about either dressing the surfaces of the valve seat or replacing the plastic seal. If the latter, be advised the new part will likely have small imperfections that will need "ironing out" by cycling the regulator some number of times before it stops creeping (more accurate to say creeping drops to a level that is inconsequential). How many times depends on how good or bad the surface is to begin with. FWIW, the lottery element associated with it is annoying to me so many times I will go ahead and disassemble a new regulator and dress the surfaces as a precaution.

There can be other causes of an erratic output pressure but the behavior you describe is almost certainly a combination of creep and just the inherent output regulation characteristics of the regulator. We have no influence over the second one but the first one we do.

Having said all that, a 10 bar swing (140-150 bar or 2030-2175psi) will have no meaningful effect on the extreme spread if you have the hammer strike adjusted to give you about 95 – 97% of maximum velocity. When you do that, the system will be operating in a similar manner as a conventional (unregulated) PCP where it self-regulates with a subtly varying lift and dwell as the pressure varies. In other words, just as you might hold a 2% ES over a 400psi range with a conventional PCP, so can it be with a regulated one.
 
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Just realized something. HUMA MAKES 2 DIFFERENT REGS for the IMPACT one is a standard and another's HIGH POWER. Which one do you have? Yo!
Click to expand...

My impact was the impact X mk1. But I did install the power plenum. And have 600mm slug liner. To achieve 950 fps, I have to set my reg pressure to 140 bar as for the Huma regulator, it's the standard gen3. I still have the amp reg that came with my gun. Maybe I can put that one back and see if it makes any difference.
Click to expand...

I would reinstall the AMP reg which came with the gun. If there was no particular reason you changed the reg, the AMP reg should be just as good, and handle the same pressure.
 
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