How to restore a Piston Regulator that has IP creep

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Since this was a Sherwood and the seat is on the piston I removed the seat and flipped it over and polished the orifice according to a Sherwood Technical Service Bulletin. It was reading about 140 psi at first and I finally shut of the air when it got to about 180. Now it is a nice, solid, 120 psi :) It's an adjustable first stage but the stop screw is frozen but 120 is fine for my air tools. I could always add a shim if needed... I also cleaned the hole in the piston and it now has air bubbling from the purge valve, albeit a bit more slowly than specified.
 
Fortunately I've found your youtube channel and followed your piston restore method.
Due to covid, I've left my mk25 on an island for almost 3 years. It was working after I got it back just with a little IP creep. so I thought maybe it's okay not service it and had about 100 dives with it. With all the corrosion buildup in side the IP creep just got worse.
Finally got all the tools and opened it up.
20230716_143548-01.jpeg
while I was waiting for the kit, I puted it back together after cleaning. It had an IP creep of 20PSI. And with new kit, still had about 10-15PSI creep. but it will luck up but takes a long time.
So I took your method gave it a polish.
The first time didn't fix it. I think I was too gentle, started with 8000.
20230723_103955.jpg
(BTW, I don't have a microscope. I was gonna use my DSLR with a micro lens and tethering to my monitor, but the camera on my phone turned out better then I thought. here is a photo of my old seat that I took just with my samsung smart phone.)
20230724_173341.jpg

1st attampt, IP creep got better and much more slower. about 10PSI in 10 minutes.
So I did it again, but this time I've started with 6000 and slowly worked my way up to 8000-10000-20000 grid.
puted it back. Voila!!!
still having 3psi creep, but like you said with new seat, it will settle after some use.
Thanks so much for all your great effort putting together all the information.
Cheers
 

Continued from previous post


Having polished the piston end, you also need to devote a little attention to the shaft. Inspect the shaft under the microscope, looking for any vertical scratches from piston insertion or removal at an angle, that may serve as pathways for leaking high pressure air. Keep in mind that piston shaft defects will not result in IP creep, but rather air bubbling from the ambient chamber holes when the reg is pressurized and submerged.

So when you get a reg for testing, make sure to do a submerged check for bubbles in addition to an IP check. If the ambient chamber bubbles, tilt the first stage while submerged, first with the LP ports up, and then with the HP end up. See if you can determine whether the bubbles come from the piston head end (piston head oring or land defect), or from the HP end (piston shaft oring or land defect). If the defect is on the HP oring land, your first stage is likely toast. Any other problem you can fix with new orings or polishing.

In any case, with this regulator, while grasping the shaft of the piston wrapped in Micromesh, twist it firmly with successively lighter grades of cloth until it is smooth under the microscope:
It is rare that you need grit coarser than 4,000 for the piston shaft. I take it all the way to 12,000 grit. It is sometimes argued that leaving the shaft satiny traps lubricant better. But any benefit from lube trapped in the coarser finish of a satin piston shaft will last only until the lube has been wiped away. I believe that a better HP o-ring seal will occur against a mirror finish, and I polish my piston shafts as smooth as I can get them. In any case, Atomic's HP o-ring is Teflon impregnated.

EDIT: My good friend @couv has taught me that I'm wrong about polishing the piston shaft to a mirror finish. He comes from a long career dealing with this very issue in aircraft hydraulic pistons, and points out that a mirror finish will increase friction. The easiest way to think about it is that a drunk driving too fast around the corner on a cobblestone street will skid. The same drunk on a smooth road will roll his vehicle.
So maybe take the shaft to 4,000 grit in removing any scoring, and leave it at that. Your HP shaft o-ring will thank you.

Only now is the regulator ready for reassembly. After reassembly per the Service Manual (including proper torque of the HP seat retainer, the turret bolt (if any) and the yoke retainer), it is time to put the reg back on an IP gauge. Keep in mind that you have microscopically shortened your piston shaft. That means that to reach the seat, the piston/spring has to compress slightly more. Typically you won't see more than 1-2 psi IP rise. But if you take out a deep nick, you may have to remove one or more shims to prevent the spring from compressing so much that IP rises out of specification.
There is nothing like the crisp lockup of a previously leaking regulator to give you confidence in your repair skills! In this case, the brief 2 psi of creep that you saw before lockup is typical of a new seat. The lockup becomes more crisp after a few thousand cycles, and IP typically rises 2 psi as the sealing edge buries itself slightly deeper into the seat, with slightly more spring compression as a result.

But how to prevent the original problem from happening again? This reg was perhaps the victim of a rusty tank, with tiny particles of iron or aluminum oxide getting past the sintered metal filter to impact the piston. And it was clearly flooded and not dried out or serviced. Though the piston land was smooth, my prejudice is still to environmentally seal the regulator so that water never gets inside again. But in any case, the bottom line is still meticulous care after a dive.

Watch for a thread coming soon on "How to environmentally seal your piston regulator."View attachment 513208
Can't tell you how grateful I am reading your great articles....
 
https://www.shearwater.com/products/teric/

Back
Top Bottom