Tuning Bad Regulator?

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jbravo103

jbravo103

Member
Jan 20, 2019
381
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North Dakota, United States
I recently rebuilt the AMP reg in my Impact X MKI hoping to reduce or eliminate creep. I replaced all orings including the action oring, piston, and washers. Before testing, I dry fired the gun about 500 times to break in the new reg parts. I probably ran another 200-300 shots (with pellets) during the tuning process. I ended up at 120 Bar shooting JSB 18.13 gr at 895 fps. Everything seemed good.

The gun sat idle for a couple weeks before I got a chance to check repeatability. So tonight I shot a string over the chrony as follows.

No. of shots: 48
Starting Bottle Pressure: 200 Bar
Ending Bottle Pressure: 150 Bar

Starting Reg Pressure: 124 Bar
Ending Reg Pressure: 112 Bar

It took about 10 shots before the fps settled in around 880. Then after 20 more shots the fps started climbing to 886-887 with 870’s mixed in. I started looking at my reg pressure and noticed after every shot my reg pressure was different. It was varying between 108 and 116 Bar, but never got back up to 120 Bar where I had previously set it at.

Not sure where to go from here except to take the reg back out and go through it again.

impact-11-13-20.1605325505.jpg


impact-11-13-20_2.1605325517.jpg

 
Eliminating reg creep is all about the surface quality of the valve seat. Both sides need to be free of any scratches, machining marks, mold flashing, etc. Anything that allows the seat to almost mate fully but not quite, allowing high pressure air to migrate slowly into the plenum until finally it climbs high enough to squish the seal fully closed.

https://www.airgunnation.com/topic/how-to-fix-reg-creeping/#post-461772
 
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Hmm, that’s interesting. Worth trying anything that’s free and won’t kill you :) You know me though, I want to know why it works or at least a plausible theory. I struggle to remember things that work by magic. My mind has to tie together cause and effect for it to stick.

I was unaware Jesus knows airguns too but I do have it on good authority he can hit a curveball!
 
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I understand creep is caused by poor sealing surfaces between the piston and set screw. In my case the reg creeps from about 112 Bar to 124 Bar, hence the reason my first shot was way low (827 fps). I don’t understand why it took another 8-9 shots for the velocity to come up and settle in.

Could this be indicative of a slightly bent valve rod?

Also curious why my reg pressure jumps around after every shot by 8 bar.

I have Huma reg on the shelf that I might throw in and see if that helps.
 
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It fixed temperamental regs from 2 of my Impacts.

Or may have been all Jesus on both occasions IDK...
Click to expand...

I agree with nervoustrig. Not saying it didn't work for you, but without an explanation of why it worked, nothing is gained.

Or is this something particular/perculiar to FX guns?
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I have to say FX guns sometimes mysteriously fix themselves. It's true!

So what other (unexplainable) explanation other than divine intervention could it possibly be?
 
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I would think that turning the reg housing 1/8 to 1/4 turn would make the piston seat in a slightly different spot at the same pressure. That may or may not be a good thing depending on the outside surface of the regulator piston/rod. Does that make any sense?
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That’s a good point. For example a new regulator often needs some break-in shots for the “soft” side of the valve seat to conform to the imperfections on the other side. In that way, they may develop a preferential clocked orientation. To then twist them relative to each other may introduce creep again.


If instead they were well mated but somehow got unclocked, you might get lucky with a random attempt to reorient them. The odds of that being successful seem quite low but I suppose it costs nothing but time so might as well try it. 
 
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Install your Huma Regulator and while your at it replace the valve pin seat with a new one, and make sure you don't have any air leaks after doing so; and check the reg air gauge to make sure it is not leaking...if you suspect it is then just replace it with a quality Wika Gauge. The valve seats are just made of Delrin and can become deformed slightly, so order a few extra from FX USA...they are pretty inexpensive.
 
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Update:

I installed the HUMA regulator and re-tuned my gun. Shooting 885-887 fps average with RP around 116-117 Bar. I left my gun sit idle for at least a week. I checked RP today and it was still sitting where I left it a week ago so I was pretty stoked about that.

I decided to shoot a string through the chrony and see how the gun was acting. Results shown below in fps, approx 5 seconds between each shot except between 11 and 12 when I reloaded the mag (about 2 min).

1 - 840
2 - 846
3 - 861
4 - 866
5 - 869
6 - 869
7 - 874
8 - 870
9 - 876
10 - 876
11 - 878
Reloaded mag
12 - 861
13 - 858
14 - 868
15 - 865
16 - 869
17 - 874
18 - 879
19 - 886
20 - 890
21 - 885
22 - 884
23 - 888
24 - 887
25 - 887
26 - 884
27 - 884
28 - 890
29 - 888

My first two shots were pretty low even though my RP did not creep. It is possible my RP did creep 1 Bar over the week, since it is pretty hard to see that on the analog gauge. It looks like things didn't settle in until Shot #19, then fps was pretty stable through #29. I can't explain what is going on from Shots #3-18. It is pretty frustrating and I'm getting to the point of just sending it back to FX for repair. I shouldn't have to shoot this gun 20 times whenever I want to take it out - that is nonsense. The gun was purchased from SPAW back in February 2019 so it should still be under warranty, however my warranty may be void since I messed with the regulator. Ugh.
 
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Could it be not enough hammer for the reg pressure, or too much reg for the hammer? I recently degassed to clean/degrease hammer and valve rod to shoot in the cold,backing out (CCW) the reg adjuster in the process. When I went to re-tune, reg was about 115-118 vs my old 110 setting but I went with it. I was getting markedly lower initial shots, 20-30 fps slower, then creeping up. If I waited 30 min and started again, slow shots. If I kept on shooting, velocities stayed up.

So I eased back the reg a little at a time. Initial shots were not as slow. When I got to 110, slow shots went away altogether. Not a big reg change, and my average velocities stayed about the same. I think my reg creeps just a bit, and with the slightly higher reg setting and after sitting awhile, pressure was too high for the hammer. Shooting steadily doesn't allow time for creep.

Could also increase hammer, but you may want to try taking 5 bar of the reg.
 
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