Creeping intermediate pressure

[halocline]

IP creep is when the pressure keeps going up and up until one of the second stages starts leaking or popping. If it just slowly increase a few PSI and then locks up and stops thats really not a creep per say.

Sorry to disagree, but any movement after the initial stop of the IP gauge is definitely IP creep, as commonly accepted in scuba regulator repair. The question is, how much creep is acceptable, and it seems to vary from one reg manufacturer to another. SP says zero creep with a new seat is acceptable, but IME they sometimes move around a little. If it stops after a few PSI and stays put for as long as you want, it's no problem.


If I understand the OP correctly, you have a MK17 with about 100 dives creeping somewhere around 5-10 PSI? About how long does it take to do that? If you leave it pressurized for an hour, what happens? Is it different with a full tank and near empty? To me, 5 is nothing I would worry about, but 10, I would change the seat. I would also change it if the reg did not hold steady IP over an hour or so of being pressurized.

If you can answer those questions, we might have a better idea of how bad it is. FWIW, the two MK18s (same seat/orifice after upgrade, which I did) that I've worked on creeped 5 PSI right out of servicing, as well as right before I serviced them. I never felt that they locked up immediately and perfectly like my MK5s. Some seats just creep a little. The MK17 has great IP recovery so setting it a little lower, as Awap says, is no problem, you'll have PLENTY of flow. What's the 2nd stage? If it's a balanced 2nd it will be more tolerant of some IP movement. If it were mine I would pressurize it, checking the IP after an hour or so, and leave it overnight. Then I might cycle it a few times and watch it. It's kind of a judgment call as to how much creep is indicative of an imminent problem.

Regarding the post about the seat acting differently in salt vs fresh water, I really have no idea where that one came from. The seat/orifice seal is never exposed to water, and IP creep has absolutely nothing to do with what kind of water you're diving in.

In this case, it can't be the HP o-ring because there is no HP o-ring like in the balanced piston stages. There are only two causes of creep in this reg, a leaky seal at the seat/orifice and a leaky balance chamber o-ring which is letting HP air into the balance chamber, where it goes through the poppet stem and into the IP chamber. That's a pretty tiny o-ring and leaks are not nearly as common as seat/orifice leaks. And it does not seem to have the same extrusion issues like the piston shaft o-rings that cause some friction on the piston and IP rise.

Sorry for the long winded post, I hope it helps some.

 

[Couv]

Good stuff from the usual suspects. I am interested to know exactly what the dive shop said. Did they indicate you have lock up within acceptable limits? If they found no problem, you might want to check your gauge. One of the IP gauges I have has a small opening that goes to the bourdon tube to prevent gauge shock. This idea is good for the gauge, but can fool you into thinking there is IP creep when in actuality the gauge is just taking time to stabilize.

Couv

 

[Joris]

They did find the creep, but thought it wasn't big enough to give a cause for concern. I'm not sure how many psi it is because the gauges here are in bar, and I don't believe the gauge I used myself is very accurate.

Right now I can't check anything at all, because I don't have cylinders at home.

 

[halocline]

Re-reading your first post, are you going on a lengthy dive trip on which there is no way of repairing the reg? Usually if I go on a long trip I bring a few tools and a rebuild kit, or just a few seats and o-rings.

Anyhow, if there is no chance of fixing your reg on the trip, you should definitely bring a back up reg.

 

[cbmech2]

Generally the diaphragm regs have very stable lockup characteristics. I am a Scubapro certified tech and have pretty much worked on the whole line minus a few of the vintage set ups. I am not sure how much of a creep you have but, there are two components that are suspect. One is the seat and the other is the removable crown o-ring. I also concur with Herman. My advice to you is to get it serviced before your trip.

 

[Joris]

Thanks everyone for all of the replies, it's great that one can get so many knowledgeable responses here.

I don't expect to be anywhere near a dive centre when I get there, so I'll see if I can have the reg serviced and dived before I'm leaving, and try to bring repair parts and/or a back-up regulator.

Come to think of it, it's kind of stupid that I didn't think of having it checked out before...



@ mattboy: FWIW, yes, the second stages are downstream override (overhauled R109 and G250V).

@ cbmech2: the removable crown o-ring would be the one in the balance chamber?

 

[DA Aquamaster]

Find a new shop. 10psi of creep in a Mk 17 is not acceptable. The Mk 16/18 seat could be a bit mushy but the Mk 17 has a rock solid lockup and you should have zero creep. If you have any it is too much. More importantly, you have 100 dives on the reg and it is most likley in need of service anyway. If you were doing local dives their advice might work, but leaving for a month long trip is really asking for a serious HP seat leak mid trip. '

In some regs, 5 psi or so of creep is "normal" as they have mushy lockup traits to start with. THe Mk 17 is not one of those regs. In general when a reg starts displaying IP creep it has not always had, something is going bad and 90% of the time the creep will get worse with continued use, the only variable is how fast it goes from bad to worse.

Also, the IP is leaking out the upper end of the range (over 145 psi), so with very little more creep the second stage will start to freeflow.

Get it fixed before you leave. I would not worry about not being able to dive the first stage before you go as if it works on the benech it will work period and it is not prone to the same break in/adjustment issues as a second stage.

 

[hg frogman]

I once had a Mk17 which began to creep after 50 dives. My LDS changed only the HP valve (a poppet with a white seat) and the sleeve that guides the poppet (a white plastic crown), and also took a look at the orifice and cleaned it with a few gusts of compressed air (both changed pieces are parts of the annual replacement kit). Then the LP was checked and found to be OK, so no need to readjust it. Overall it took 10 minutes and the reg served me well for more than 200 dives after that.

The same thing happened to one of my wife's Mk17 after about 80 dives. Same process but this time the tech had to slightly readjust the LP and that took 5 extra minutes.

In both cases the seat was the cause of the creep, but in some other cases the cause can be the small o-ring(s) sealing the balance chamber of the first stage.

With the HP seat being the most critical point of a diaphragm reg, if it begins to creep it's time to change it, as DA Aquamaster says. In my experience with the Mk17 the seat can last from 50 (if you're unlucky) to 200 dives (if you're lucky) but most probably around 100 dives.

BTW, to make sure there's a creep or not, it's not always enough to look at the needle showing the LP (especially when you use a small gauge), you may also have to immerse your second stages in a bucket of water to make sure there's a free-flow (even very slight : a small bubble every 15 seconds, for instance) or not. When the HP seat is leak-proof, it's REALLY leak-proof !

It's very handy anyway to bring your spare Mk2 as you're planning to do. Enjoy your trip !

 

[Joris]

I've just collected the reg from another check at a dive shop. They've had it pressurized for a day, and used a reliable gauge, and the creep is actually a lot less, less than 5 psi.

They couldn't have it serviced before I'm leaving, but they've adjusted the interstage pressure, and I'll bring plenty of spare equipment, so I should be fine. Thanks for all the advice!

 

[divedrewsf]

Hi - sorry to revive a very old thread, but it just goes to show that there is such great info contained in this board!

I just overhauled my MK11, and it's holding pressure steady at 133. Second time overhauling this one and it's super easy. I also overhauled, for the very first time, a MK25, which has been my primary for the past year+ (around 100 dives). FYI, the MK11 was also used somewhat regularly this past year+ by a buddy, but not quite as many dives.

Anyway, first time overhauling the MK25 and it also was pretty easy. But I am seeing some IP creep...just a bit. My gut is that the HP seat is just settling. I think I will try to cycle it and see if it improves. The only thing is that I use a small 7ltr tank for my overhauls so I'm not sure how much air I will have before needing to fill it. I know I know....I need to get a larger tank (I live in Manila so don't have the room for a proper bench). LIve and learn. Haha.

Anyway, thanks to all who contributed to this thread. Very helpful!


EDIT: as a follow-up....yes, cycling the reg has settled the HP seat and it's holding steady now at 138. An observation: although my sample size is tiny (one, ha), I have noticed that the piston (MK25) reg will drop about 5psi on a cycle/breath then slowly creep back up and hold. The diaphragm (MK11) reg appears to behave differently by dropping on a cycle/breath then sticking right back where it started (little to no creep back up). interesting!