Signs of a failed regulator?

[Kragman1]

Hi all

I have a new to me DAR Gen 3 in .22 that is acting strangely, at least to me.  Keep in mind that this is the first time I've owned a regulated PCP, and I'm starting from zero, knowledge-wise.

I was getting around 425 fps with a 90% filled tube and the hammer adjustment set to be flush with the rear of the action.  I was able to turn it in roughly 3 full turns then back it out 1/8 turn or more, which got me up into the 600 fps range.  However, for the next three magazines (30 shots) the velocity increased by roughly 10 fps for every shot until I was into the 900's and making 33-34 fpe.

I don't understand that.  Even if the regulator simply didn't work, I would expect the rifle to perform like an unregulated PCP. 

So if anyone can point me in the direction of a solution, I'd really appreciate it.  Hopefully, I'm doing something dumb since getting to the regulator adjustment requires more disassembly than just popping it out of the stock. And I'd be perfectly happy with the OEM setting.  Not looking for max power.

Tha ks all!

[billygee]

Some regulators are kinda finicky and need to be Degassed before any adjustments

Did you Degas before adjusting the regulator ?

Bill

[nervoustrigger]

The behavior you describe is that of a regulator that has experienced a failure of the seal on the adjuster. 

The DAR gen 3 regulator is similar in construction to a Huma regulator:



The adjuster is the brass part on the bottom right.  What happens when its O-ring fails is reservoir pressure bypasses the regulator and feeds directly into the plenum.

[Kragman1]

Thank you guys.

Bill - no, I did not.  I didn't expect.to need to do anything like that.

Nervoustrigger - that what's I imagined might be happening, but I still don't understand why the rifle doesn't simply act as if it's not regulated, rather than going through the long steady climb....

Well, I'll have to see what I can do about it. 

Life is an adventure!

[nervoustrigger]

I still don't understand why the rifle doesn't simply act as if it's not regulated, rather than going through the long steady climb....

What was the reservoir pressure when you stopped shooting?

[Kragman1]

I don't remember exactly NT, but somewhere around 1300 psi maybe.
The next night I ran another mag though it - it climbed again for the first 4 or 5 shots then began to decline steadily.  So I assume the regulator is doing something....

[nervoustrigger]

I don't remember exactly NT, but somewhere around 1300 psi maybe.

Okay yeah that is consistent with what would be expected when a regulator goes into bypass.  In other words what you were observing was the gun started at a state of partial valve lock due to the high pressure of the reservoir making it difficult to knock open.  As the pressure fell, the velocity continued to climb and then eventually plateau and begin to decline.

[Kragman1]

I didn't see a plateau, but I can follow what you're saying.

My chrono isn't trustworthy after a fall, but I'll see if backing.off the hammer by 1 turn gives me steadier results.

Any thoughts on a fix?  If I need a regulator, is there an aftermarket improvement over the DAR one?


UPDATE:  just backed off nearly 1 turn, pressure 90% of max, fired 10 shots - started at 559, ended at 607, steady increase starting with roughly 10 fps change for the first shot or two, only 2 or 3 for the last few.

[billygee]

Something to consider as to :

Increasing pressure to regulator W/O Degassing can cause damage to the regulator

Bill

[Kragman1]

Would making a large adjustment to the hammer spring be able to damage the regulator? 

[JimD]

Brian,

I don't think there is anything you can do with the hammer spring that will damage the regulator.

I would try filling to lower pressure and see if you don't get more typical unregulated gun behavior.  I think the tank pressure is too high for the hammer spring to fully open and as the pressure falls, the valve opens better and the velocity increases.  Then later when the pressure is low enough the velocity starts to fall.

I had to rebuild the Huma regulator in my Caiman X after about 100 shots because it completely failed.  I was a little reluctant but it was easier than I thought.  It had much too much silicone grease in the spring washers and none on the O-ring on the adjuster.  I fixed those things replacing no parts and it works great.  It's important to keep track of all the little parts but otherwise I think regulators are not a big deal.

Jim

[billygee]

I failed to include increased pressure against the  (depending Lft or rt handed thread)
 spring or washers assembly W/O degassing can cause damage

Hammer spring tension applies to the amount of timed air applied to the port

Usually there are procedures on regulator adjustments in user manual

[shaky2]

Same thing happened to my Dar Gen 3.. I knew it was a reg failure so I ordered a Huma Air Reg and its been great since. That was well over a year ago.I did rebuild my old reg to have for a spare and the reg adjuster oring was falling apart when I took it apart

[nervoustrigger]

A brief public service announcement regarding O-ring longevity with pressure regulators.  The two smallest ones—the one on the brass adjuster and the one on the small end of the piston—are subject to heat stress which causes them to become brittle over time.  In my experience, the overwhelming majority of regulator seal failures are of this sort.
 
Switching from Buna-N to Viton for these two will improve longevity.
 
True to the trend, the regulator on my DAR gen 3 failed in this manner.  I rebuilt it using Viton O-rings.  While I had it apart, I noticed the conical orifice at the end of the adjuster was tall and sharp compared to most regulators.  In other words, it looked like it would dig into the sealing disc pretty aggressively so I decided to blunt it slightly by wet sanding it and then polished the tip.  Pleased to say it has been working splendidly.  The setpoint is very stable and I can leave it idle for days or weeks and the first shot is always spot on.

[Kragman1]

I want to thank everyone for taking the time to give me such good info.  You guys are killin' it!

I'm swamped at work (pulling a double tonight for example) so it will probably be a while before I can do anything with it.  But I'll be looking forward to it.

Shakey & NerousTrigger - do you recall what size O rings, etc that I'd need to do a rebuild?  I'd like to have everything on hand when I pull it apart, so I'd like to order in advance.

Thanks again!

[nervoustrigger]

Here's a copy of my notes with the O-ring sizes:

Code: [Select]

O-rings
=======
* tube end caps: M2.5x21 2ea
* tube segment for regulator & gauge: M2x20 1ea
                                    M2.5x21 3ea
* regulator body OD: M2x14 2ea
* regulator spool top: M1.5x9.5 -> OEM one seemed fine after ~1.5y despite other two reg O-rings being compromised
* regulator spool bottom: M1.5x3 -> OEM one was semi-brittle after ~1.5y, replaced with -005 Viton with its ID abraded using a conical diamond until it was reduced from 0.070" to 0.060"
* regulator adjuster (brass): M1.5x4 -> OEM one was brittle like plastic after ~1.5y
* Foster check valve: M1.5x3, used -005 to replace it
* air tube assembly to receiver: M1.5x17 2ea
* valve body insert (brass): M1.5x9 3ea -> the one that holds pressure was extruded after ~1.5y, replaced with -011 70duro HNBR

gauge uses a Delrin washer
Foster uses a Delrin washer

And here's a photo of the gen 3 regulator courtesy of Privateer: