REGULATOR CREEP OR SLOW LEAK?

Forums PCP Airguns REGULATOR CREEP OR SLOW LEAK?

  • Views : 344
  • Link

    CHUCK
    Participant
    Member

    Here I will attempt to shed some light on a friend's recent problem with his Wildcat .30 MKII that he mistakenly referred to as "regulator creep", in the hope that others may benefit from this explanation also. First, let me tell you what happened…

    Not long ago he bought a used Wildcat .30 and then recently installed a new Huma regulator under my supervision over the telephone. I taught him how to install the new reg, set the feeding pin's depth, and how to adjust his hammer spring tension. When he would shoot the rifle over his chronograph with just a second or two between shots the numbers he got were all very close to each other…but when he would let it set for say a half an hour and then shoot it over his chrono his first shot would be much lower than expected. But after that first low shot all the others would be where they should be. 

    As a newbie he jumped to the conclusion that his rifles' problem was due to the dreaded "reg creep" problem erroneously described here on many occasions. "Reg creep" would result in his first shot being abnormally higher than his other shots…not lower. The problem with reg creep is caused by two basic problems…either the regulator valve is allowing a little extra air to "creep" past into the plenum space over time, or the o-rings on the regulator are allowing a little air to "creep" past the regulator into the plenum space. Thereby causing the regulated pressure of the air in the plenum to be higher than normal, subsequently causing the first shot to hit higher on the target than the ones that follow it.

    This is a fairly common malady that can be cured by cleaning and reinstalling the regulator, replacing the o-rings on the regulator, setting the regulator to a lower or higher pressure & tuning the hammer spring tension accordingly, or if all else fails the regulator itself can be replaced with a quality regulator known for its precision and reliability…of which there are several brands available.

    So since my friend's problem was not "reg creep"…what was it? Well I told him that more than likely his problem was a simple air leak, and pointed out all the places he should check with some leak detector. After some investigation he discovered air leaking out of the vent hole in the air tube…a simple problem to solve by installing new o-rings on the regulator. The problem he encountered can be incredibly frustrating to diagnose and isolate. An air leak on the plenum side of the regulator will cause the pressure in the plenum to be low, thereby causing the first shot to hit low on the target.

    One thing that can be very frustrating is that the air gauge may appear to show the same pressure as it did hours or days or weeks in the past, leading us to think there is no air leak. A very slow air leak on the plenum side of the reg can leak out enough air for the first shot to be abnormally low, and yet not have leaked out enough air to cause the reg valve to open and refill the plenum. This can be maddening to figure out if you don't know what to look for or to find even if you do know what to look for.

    Below is a picture of a pesky air leak I had at the Dowdy washer (rubber steel washer) where the air tube connector seals against the rear end cap of the air tube. I had been using an eye dropper or an Allen wrench to put big fat drops of soapy water on this very spot but it didn't show a leak until I sprayed some soapy water on the Dowdy washer with a little spray bottle. Even then it would take several minutes to show just a few micro-bubbles…but after awhile it would show a pretty good sized ball of suds and revealed the leak.

    So don't automatically jump to a false diagnoses of "reg creep" if your first shot is hitting lower than all the subsequent shots…and don't immediately convince yourself that you need a new regulator either until you have explored all the possibilities. True regulator creep is usually caused by a tiny spec of dirt inside the reg or old dried up shrunken o-rings on the outside of the reg itself. 

    Below is a picture of the most elusive leak I ever encountered on the plenum side of the regulator. Hope any of this helps someone to have a better understanding of these problems.

    All the best, Chuck

     

    • This topic was modified 5 months ago by CHUCK.
    Link

    Dairyboy
    Participant
    Member

    Very interesting. Shouldn't the reg refill itself when the pressure is leaked out?

    Link

    ghoststalker
    Participant
    Member

    That’s very cool of you to help him out the way you did ! There are still some good people after all.

    Link

    zx10wall
    Participant
    Member

     "Reg creep" would result in his first shot being abnormally higher than his other shots…not lower

    Chuck, reg creep definitely causes the first shot or first several shots to be low not high, at least if the gun is tuned half-way decently. This is because the plenum is being charged to a higher than set pressure due to the “creep”. Because the hammer strike is not changed to overcome this added pressure, the shot(s) are lower than normal. 

    I’ve known a valve-poppet to have a slow leak. It would leak plenum pressure because that’s where it’s supplied from. It never showed a “creep” symptom because the reg keeps feeding pressure when called upon. It would have to be a gusher for the reg to not fill faster than the leak can dump. A plenum is filled by the reg in a few seconds.  

    I think your friend does have a reg that’s creeping. It sounds like he also has a leak to address being that he found one. Just my .02  

     

    • This reply was modified 5 months ago by zx10wall.
    Link

    nervoustrig
    Participant
    Member

    In the scenario you are describing, the first shot would not always be slow.  When there is a leak on the plenum side, eventually the pressure will fall enough that the valve seat will open and top off the plenum.  Thus sometimes the first shot would be slow and other times it would be normal.

    Is that what you observe?  I got the impression from Augie that the first shot was always slower than expected.

    As to the usual cause of creep, I agree it may be a bit of debris trapped in the valve seat but it has been far more common in my experience that it is due to the surface quality of the valve seat.  Many times I have remedied a creeping regulator by dressing the surfaces carefully with fine wet/dry sandpaper.  I reasoned that debris doesn't tend to get trapped at the seat because of the very high velocity of air rushing to fill the plenum every time a shot is fired, it will usually just blow right on through.  To get stuck in the seat, it would need the unfortunate coincidence of being timed just right to get pinched and squeezed into the soft side of the valve seat right as it is closing.

    Link

    JoeKool
    Participant
    Member

    This can be true.  I have just replaced the o-ring opposite of that dowdy seal on my Wildcat MKII .25 after discovering leaky bubbles there (like your picture but nearest the block side). This leak was significant enough to drop from a full 230 bar to 50 bar overnight.  My gun has had a Huma regulator installed for a good while now (working well, untouched) but started strangely, erratically, and randomly shooting a low velocity shot.  It’s tuned to shoot JSB MKII 33.95 grain at 850 fps.  Over the chronograph randomly it would shoot 850’s, 850’s, 850’s, then 775, and right back up to 850’s fps again.  After repairing the leak the velocity is again consistent in the 850 fps range from the first shot to the last.  Never touched my regulator or hammer spring during this o-ring change.  

    Airguns in general have potential to hit you with issues that seem way out in left field.  Systematic troubleshooting, logical thinking, some understanding of the guns mechanics, and a little luck has helped me fix so many different issues on various guns that I’ve lost count.

     

    Link

    2fast2furious
    Participant
    Member

    Like someone stated. Reg creep will make the 1st shot low.  This is due to reg creeping making the reg pressure higher. You think higher pressure means faster fps. But no. Higher reg pressure means the hammer cant struck it hard enough to open all the way. That's why you get lower fps. My impact stock amp reg will shoot 820 1st shot. Then 840. Then 3rd shot and after will be around 860-870 fps. So reg creep does not mean higher fps.

    Link

    nervoustrig
    Participant
    Member

    Reg creep can cause either a slow first shot or fast first shot, it just depends on how much hammer spring tension is dialed in.

    Link

    leadfoot
    Participant
    Member

    I was under the impression that a recognizable symptom of reg creep is that your reg pressure gauge would show a higher BAR number than normal, 

    As explained above, you would guess that would result in a higher velocity shot, but if your hammer spring is not able to overcome the valve opening resistance you would get a slower shot. It could happen either way. Very interesting.

    Link

    CHUCK
    Participant
    Member

    The increased pressure in the plenum caused by air creeping past the regulator rarely would be enough to hold the valve pin shut and require hammer spring tension adjustment.

    We're talking about a shot hitting higher on the target 1/2 inch or 1 inch higher on the target with a slight amount of regulator creep, just enough to be annoying … and an increase in velocity of 30 feet per second or thereabouts.

    The same applies to a shot hitting 1/2 inch or 1 inch low on the target because some of the air has leaked out of the plenum… it's normally only 30 or 40 feet per second less than the other shots, but the problem clears up immediately after a couple shots have been fired.

    Neither one of these scenarios are all that dramatic, just very annoying to people like me with overblown OCD!😂

    All the best, Chuck

     

     

     

    • This reply was modified 5 months ago by CHUCK.
    Link

    lenweber2
    Participant
    Member

    Some confusion here? Low trajectory or low velocity? Regulator creep should mean higher pressure on the plenum  side of the Rev, higher the pressure should equal higher velocity  lower impact point. I think, lol.

    Link

    zx10wall
    Participant
    Member

    Think of an unregulated PCP tuned with a good bell-curve. Let’s say you fill to 210 bar and shoot to 135 bar. The shot string would look like this: Begins at 860 fps (210 bar), peaks at 890 fps (175 bar) and ends at 860 fps (135 bar). You know that you should only fill to 210 bar max to begin the string at 860 fps.

    If you were to fill to 225 bar, the valve is not going to open as it should when the hammer strikes it at the set hammer spring tension. You would get what’s referred to as “valve-lock”.

    Instead of 860 fps you would see 825 fps or so. Each shot would gain some speed until you get back to 210 bar and you would get the 860 fps. A similar situation is going on when your regulator creeps and allows the plenum to over pressurize.   

Viewing 12 posts - 1 through 12 (of 12 total)

You must be logged in to reply to this topic.