Fall first-stage rebuilds that are O2 “clean enough”

I discovered that my car battery was dead Thursday morning before work so I figured I would work-from-home and use that opportunity to do something truly productive. I figured I would catch up on a little scuba gear maintenance and rebuild some regulators, specifically first-stage rebuilds. All in all, it was a very productive day. I rebuilt a bunch of my regs that were well overdue.  I have a bunch more that I’ll save for a rainy/snowy day sometime this winter.

Why Rebuild Regulators?

My philosophy for most regulator rebuilds is simply..don’t do it.   I realize that this goes against everything the dive industry tells you but if you know they have not flooded and they are still holding solid IP without showing any signs of high pressure creep then you know they are “probably” good.    Servicing something for the sake of doing it is stupid especially if you have a perfectly functioning and in-spec regulator.  You risk introducing another problem.  It’s the old adage “if it ain’t broke, don’t fix it.”  Having said that, my opinion on regulators that see high concentrations of O2 (deco regs with o2/50% or first stage on O2 side of rebreather)  is that these should “probably” be rebuilt more frequently if you want to maintain something of an “O2 clean enough” status.  Even that is argued by some people but I do like to try to rebuild my deco/stage regs every other year.     I typically do first-stage rebuilds a lot more often than second-stage rebuilds provided they are not leaking or free flowing.

O2 Clean

The whole “O2 clean” requirement is something that is very hard, if not possible to adhere to in the diving world.   Once you use that regulator multiples times in a non-O2 clean environment or get a tank filled from an unknown source then your precious “O2 clean” status is suspect.  The best anyone can truly hope for is O2 “clean enough.”   I treat pretty much every regulator rebuild as if it needs to be O2 cleaned, using vinegear, simple green for cleaning and tribolube for any parts that require lubrication.

On to the rebuilds..

The first regulator on the chopping block was my generic Highland/XS Scuba suit inflation first stage. I’m pretty sure that thing has flooded multiple times by now but I have not bothered to rebuild it since I had a backup Apeks DS4 that I was using for suit inflation.  It was purchased new in 2013 at the beginning of the season so it has some miles on it and has not been serviced since then.   It’s pretty easy to take apart, you just need a pin spanner to remove the cap where the piston is.   After that it’s a bunch of generic o-rings easily sourced and a generic HP seat.   The parts were given a quick dip in the ultrasonic cleaner with a hot water / white vinegar bath. They came out looking clean and good as new.


I had a service kit but I admittedly didn’t bother using it.  I inspected the o-rings, replaced those that looked worn or needed to be replaced and I flipped the HP seat over to the other side.  This particular reg you can actually re-use the HP seat by flipping it over on the other side. Of course no manufacturer is going to ever tell you to do that.  I also rebuilt the OPV on the first stage. The highland/xs scuba first stage is a really simple piston design that is easy to rebuild.  I had ordered a service kit from DiveGearExpress since I was/am pretty sure the DGX suit inflation first stages are the same reg; I’ll keep it as a spare kit.

The next first stage I needed to be rebuild was a HOG D1.  This is one of my backup stage/bailout regulators.  I think it unfortunately flooded in salt water about 6 months ago so it needed to be rebuilt since the IP was not holding at all.    Upon opening it up it was pretty obvious that salt water had gotten in there.  Not terrible inside but meh.  Surprisingly it was definitely “cleaner” than some regs that I’ve opened that should have leaked but didn’t.

Overall I don’t mind HOG regulators.  They are essentially knock off Apeks clones that are very easy to rebuild and part kits are readily available.  I haven’t had nearly the same problems that some other people on the Internet claim.  Some people like to spend to lots of money to have “the best” to justify themselves.   The only issue that I’ve had with HOG regs and I guess it’s a big one is that they don’t seem to nearly last in service quite as long as my Apeks regs do.  For example, my Apeks can go 2-3 years+ without rebuilds and the IP will hold fine.  I would say my HOG regs are 1-2 years before I start noticing IP creep.  Different quality HP seats I don’t know?  I would say that part of the reason maybe is because I use HOG first stages on a lot of my deco and bailout bottles which are more likely to flood than my singles/back gas first stages I guess.  Either way I am not really going to replace them at this point unless I can find some really cheap Apeks DSTs or DS4s for the right price.

Since I do use this reg interchangeably on my 50% and O2 bottles an “O2 cleaning” was warranted…  First a dip and water/vinegar in the ultrasonic and then a dip in a solution of Simple Green, followed by fresh water rinse. Probably overkill but I figured I had the time so I might as well do it.    The HOG D1 rebuild process is almost identical to rebuilding an Apeks DST first stage. Minor differences in parts but if you can rebuild an Apeks first stage then you can rebuild a HOG first stage and vice-versa.

Once assembled the D1 first stage held steady IP without issues.  I de-tuned mine to around 125psi for cold water although the manual says to put it at 135psi (+/-) . It’s a habit/something I learned a while back although I’m not actually sure if it makes a huge difference.  According to the HOG service manual, you need to “Repeatedly purge the second stage or open and shut the test gauge bleed valve at least 100 times to ensure that the intermediate pressure locks up consistently.”  That seems little excessive but I probably did it about 25-30 times for good measure and left it on a tank with 3100psi for few hours and then did another round of purging while I was catching up on work emails.

The last regulator on the chopping block was the Apeks DS4 on the oxygen side of my rebreather.  According to my Petrel it has something like 325 hours of use so I think it was definitely time for a rebuild.   I had a minor issue with the constant flow orifice in Scapa Flow leaking way more O2 than normal but when I put the reg on an IP gauge the IP held steady without any creep.   I checked it several times and it still did not creep but I suspected it might have issues.  Later I discovered that the fitting on the orifice had actually cracked and was leaking O2 at the fitting.  Long story short but nothing a 4GBP 1/8″ BSP plumbing fitting couldn’t temporarily fix. Not too many hardware stores in the Orkney Islands of Scotland!  It was probably my fault I took the orifice apart to clean it a few months back since it was clogged and I may have over-torqued the brass fitting.  Either that or the IP went way too high and contributed to splitting/cracking the fitting. I decided to rebuild the first stage anyway since it was probably well overdue.

It might have gotten a little water in it at some point but didn’t look too bad inside at all.   I essentially repeated the same process as the HOG D1.  A bath of hot water / vinegar, followed by a Simple Green solution in the ultrasonic cleaner and then a fresh water rinse.  I figured I probably should make a valiant attempt at O2 cleaning this first stage since all it ever sees is pure O2. 🙂

The only real difference between the Apeks DS4 on the rebreather and a normal Apeks DS4 is that the Hydrostatic Load Transmitter is removed and the environment seal is capped with a solid blanking plug that essentially disables the depth compensating ability of the regulator to sense outside pressure thereby converting it into an absolute pressure regulator for use with a constant flow orifice.   Lots of fancy words there, sorry.   What does this mean? Well for me it means you can simply use the normal Apeks rebuild process and use the same Apeks service kits.

Rebuildng Apeks DS4 First Stage

Speaking of which I realized that my personal supply of Apeks service kits was dwindling so I had to order some more on eBay since they are getting a little harder to source.  Luckily there are still sellers in Germany that have plenty of Apeks kits so I stocked up on some more.   I had a friend of mine swing by because he needed a service kit for one of his Apeks DS4 so we rebuilt that one as well..   I love how easy Apeks DS4s are to rebuild..

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