Tuning Reg. Creeping Down

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Drumsnguns

Member
Jun 14, 2016
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North Carolina, United States
Well I’ve heard of regs generally creeping up but on my Impact MKII it creeps down. This is the FX AMP Reg. set to 164 bar. Three times now I’ve had to bring it back up from 154 or 157. And this happens within maybe 1/2 to 1 hour. 


Does anyone have an idea as to why?

I have a high pressure Huma that I might swap in. Been experimenting with higher reg pressures for slugs. Seems to improve things. 


Thanks. 
KP
 
What follows may not be the answer but perhaps will help get the brainstorming going.

Once a regulator has reached its setpoint, it needs to experience some amount of pressure drop before it will reopen and top off the pressure back to the setpoint. How much of a drop it needs to see will vary from regulator to regulator depending on a number of things, among them the nature of the spring rate & travel and the compressibility of the valve seat material. So perhaps if the plenum has a slow leak, that could be what you’re seeing. A 7 – 10 bar delta is a lot though so I kinda doubt it.

At the very least we can say the following:
1. The only way the plenum pressure can decrease is if it loses air or if it cools.
2. If it isn’t either of those, it means the gauge is somehow lying.
 
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I'll have to do a leak check this evening.

I have not noticed a leak on the gauges and I'm using Sekhmet gauges so I trust them over the analog gauges, (though no gauge is truly accurate).

What happens is I take the gun out of the case and check the reg and lately its been lower than when the gun was put away. I fire a couple of shots and sometimes it resets to the proper setting and sometimes not.

Yesterday while shooting I noticed twice that the reg pressure had dropped down from around 160-164 to 157 or even 154. So I upped the reg back to 160+

I'll check it this evening and see what it's settled to. 

I know that low temperature can decrease plenum pressure but I'd think that the reg would keep supplying air to the set point.

But as always, open to suggestions.

Thanks

Edit: I might pull the reg and check o-rings and give all mating surfaces a good polishing with 3M polishing paper. That might be what it needs. I've just never seen the pressure go down with creep.
 
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Swap it out for a Huma and never worry about the reg again.
Click to expand...

If only it were so simple. 


@Drumsnguns I initially thought you may have a leaking reservoir. Then when you said the reg pressure increases after a shot, @nervoustrig’s idea of a plenum leaks makes sense. I haven’t heard of regs going down other than when the reservoir pressure falls below the reg set point. Had the gun been sitting unused for a long period of time prior to this issue? Are you sure that you took the proper steps to adjust the regulator? I’m not an experienced technical person in this area, but I’ve run into a couple regulator issues myself. I am curious as to what you find at the root of the issue. 
 
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My Impact sometimes does it after a tuning session. Sometimes it takes me a couple days to get it to stay put. And when I say a couple days, that doesn’t mean me messing with it 24/7. It’s just one of the side effects of a digital gauge that makes us dysfunctional. A normal gauge guy would never notice it and is probably better off. The creeping down or sticking down a couple bar hasn’t even messed with my slug tune but because I have 127b written in my note book, my dumb ass won’t stop until I get it settled right on 127b.
 
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Hi guys, thought I'd report the latest....oh, and BTW, thank you for your responses!!!

I took the AMP Reg out and examined. There was a good sized fiber on the reg body which may or may not have been across an o-ring, I just don't know. But the AMP Reg has always had a bit of a slight creep problem....not much mind you but never the downward creep before. So I decided to install the HUMA Extra high pressure reg I had on hand.

This is a "slug" Impact so I'm going for higher speeds, (and higher reg pressures), like around 960-980 fps for the 38.9 gr NSA. 

I tuned the gun with the Huma and got my target speed of 970 fps at 145 bar. I like to add 3-4 bar on top after the tune to kind a bed things down and that put me at 149 Bar. That's where I left it last night around 7:30. Checking today, about 17 hours later, and it's still sitting exactly on 149 bar. This is a good sign, but unfortunately, this weekend we're having sustained 20-25 mph winds on top of gusts so no-go for checking things. (So tired of windy weekends in this part of the country)!

Anyway, once I get a chance to see how things shoot I'll report back.

Weather says windy all week...UGH!

Cheers,

KP
 
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