Huma reg. belleville washer stack losing "springiness"?

No clue but good luck at EBR Mike My the winds be in your favor.

Now bevel washers come in differing thickness's and how configured with differ. HuMa does offer a few variants with many of there regs based on models specifics and pressure range of adjustablity.

IMO ... if you were using a Reg calibrated to be used at the lower bar ranges at pressures much higher, then the preload on the bevels will be very high when the spool has moved far enough to close the seat. so much so the bevels are nearly flat and won't have good memory / tension stability & won't hold the set point well either.



just sharing ...

I dont know about the reg in the bobcat works, but if it were my Crown I'd think the reg adjusting screw was turning out, increasing the pressure.

If you complete empty the air out if the gun, and then recharge it the reg would be where it was when you purged the air if I'm right.

Mike, I had a similar problem years ago with my Wildcat .25. I cured the problem by removing the little 4 mm screw that sets down inside the brass adjustment screw on my Huma. Best regards, Chuck

Fatigue is something to wonder about. Seems it was definitely more common when I was much younger to see springs fatigue. I read several articles quite a few years back concerning this concept with CF magazine springs and they predominantly said it was rare to have fatigue in modern magazine springs. I have a handful of pistol magazines that I've kept loaded for long periods and they always function normally with no tactile change in pressure. Maybe spring making techniques are better now. Don't know specifically how this would apply to bellevilles but they are springs.

You have leakage between the hp oriface and seat. Very small but allows the lp pressure to creep up. When the lp side creeps up it put an indentation in the seat effectively adding distance, this is equivalent to backing out the adjuster. When you readjust your are compensating for the damaged seat and the cycle repeats.

Look for damage or debris on the hp oriface face and replace the seat again. These surfaces must be perfect. Use a good magnifier to inspect.

A weak spring stack will lower your set point.

Centercut, have a look at this fatigue life chart...



...even for the high travel (low preload and high upper stress) where fatigue is highest, it shows in excess of 100,000 cycles. Or more than 2 million cycles for low travel setups. Granted we don't know how much deflection the springs in the Huma reg are experiencing in this particular case, but for a gun that has an adequate plenum volume and the hammer strike adjusted properly, the pressure drop during the shot cycle will be fairly modest. Thus the deflection and fatigue would likewise be modest. So for the behavior you're seeing, fatigue does not seem to be a plausible explanation. Well, unless you shoot ten thousand pellets every few days

As to the question of whether operating Bellevilles near the top end of their range, such that they are nearly squeezing flat, I could not find a good source that addresses this question to my satisfaction. However I know they are commonly used in bolted connections to maintain thread preload, and are frequently squeezed flat in this application. Also, manufacturers often give the flat load rating. If it were bad juju to squeeze them flat, I would expect the spec sheets to give a "max usable load" or "max deflection". Lastly, manufacturers of quality Belleville springs will pre-stress them by squeezing them flat. Solon Manufacturing, for example, says "the spring will no longer yield during subsequent loadings". Taking all these things together, I do not think squeezing them flat is a problem.

With that said, a stack of series Bellevilles like is used in airgun regulators, e.g. ()()()()(), I perceive an elevated risk of inverting one or more of the washers in the stack if it's pressed to the limits. The runt of the litter may be just a little weaker than the rest due to manufacturing tolerances, so it could get turned inside out and permanently damaged. Worse still is this risk if a modified stack were used. For example, the lone washer in the middle of this stack would lose out (( )) ( )) ((. However this type of damage would weaken the stack and the setpoint would fall, not climb as it's doing for you.

So what is the likely cause? Well, I can think of just two things. One is a valve seat that is starting to show signs of wear. Could think of it as creep or just a logical consequence of the piston having to move a tiny bit more before the flow of air is halted, thus the pressure climbs just a bit higher over time.

The other possibility is along similar lines. If the gun sees big temperature swings, the seat may be getting indented. That will cause the setpoint to migrate upward. Let's take a hypothetical example...let's say the gun has a 2000psi reg setpoint and it gets fired at a modest temperature of 70°F. Later on the gun is left in a car in the summer sun and the temperature climbs to 130°F. The plenum pressure would increase to about 2200psi, squeezing the piston hard against the seat and potentially indenting it. From here on out, the piston has to travel further to reach the seat which means it now has a new higher setpoint.

That's about all I can think of. Good luck! Keep us posted, I'd love to hear back when you find the culprit.

No problem! It sounds like you have your hands full. Good luck at the EBR next month. 

Holy krapole! And all this time I though aN EBR competitor just showed up with one gun!! Man, you are seriously into this CC. That just means I need to get more guns. Think my wife will understand? 



Lets see- got a PRod for the 100 yarder, got a 14 lb hatsan hercules Bully 30:cal for the FT event, cause one has to move fast, and the large pellet will for sure hit those targets, got the 25 cal Marauder for whatever finals that I get into, and my Wildcat as back up if needed, but I doubt it, not with that PRod. 



Im good!!