Scubapro MK20 Maintenance Issue/Question

[aquaursa]

Hi -

We're trying to figure out what went wrong with my girlfriend's MK20 and want to be prepared to have the discussion with our LDS by seeking out your input. (We had a previous failure due to improper maintenance with the shop and, although we don't want to automatically assume their fault, we also want to go into the discussion with our eyes wide open.)

The gear:
* MK20
* S600
* AirSource Power Inflator Octo (like Air 2)

Serviced annually. No noteworthy repairs beyond standard parts replacement. MNK20 was purchased new; has 800+ dives on it. Was serviced just prior to our December dive trip.

Approx 10 dives into the trip, the 2nd stage began to vigorously free flow after air pressure was turned on (she might have bumped the purge button while gearing up, but free flow was constant until she put her thumb over the mouthpiece).

On a subsequent dive we heard air flow coming the 2nd stage prior to the dive (not a vigorous free flow but noticeable); the DM grabbed her 2nd stage and increased resistance the inhalation resistance control.; he may have also adjusted the VIVA.

On Dive 16 we noticed significant airflow coming from the AirSource power inflator octo (like Air 2) through the gills. By significant I mean: constant, with large bubbles.

On Dive 17 tried a replacement inflator hose, but then the octo free flowed at a low rate, we believe she lost 200 PSI in 15 minutes (based on our normal SAC)

The liveaboard's technician tested the IP and came up with reading of 180, which he said was beyond the 135 or 140 that the MK20 should be delivering.

Before we take this in for assessment, we'd like your thoughts. Seen this before? Possible causes? User error?

Thanks. Please let me know if I can clarify any statements or add to the detail.

Tracy (aquaursa)

 

[dumpsterDiver]

I would take it back, tell them the IP was way too high, you just paid for a full service, it messed up your vacation dives and you want it fixed, presumably for free.

It amazes me that people spend a ton of money on service and gear, but don't own a $10 IP pressure checker guage..

 

[redacted]

with IP of 180. there is a clear problem. But had that been the condition coming out of service, there would have been a problem on the first dive. I would guess you are looking at a defective HP seat.

Get an IP gauge so you can inspect your gear.

 

[johnnywulff]

Normally when the high pressure seat is replaced it has to be cycled minimum 15 time's to re ajuste the IP, because it's making the initial groves in the seat, that's why it was fine at the firsts dives or at the LDS

 

[halocline]

You have what's called IP creep, meaning your intermediate pressure has risen way beyond what the 1st stage is supposed to provide. It's either the seat as awap said or the piston. Those are the only two possibilities for IP creep like that. Some MK20s have a piston with a brass tip, and those are very susceptible to IP creep. If yours is one of those (ask the tech) you should replace it with a new composite piston, the one that comes in the MK25. That will fix your IP creep for sure.

If you've owned this reg since it was new and it's still under warranty, this should be a free repair. If not, expect to pay about $60 for the piston if you need it.

 

[halocline]

Normally when the high pressure seat is replaced it has to be cycled minimum 15 time's to re ajuste the IP, because it's making the initial groves in the seat, that's why it was fine at the firsts dives or at the LDS

Nope, not in this case. THe MK20 uses a rounded tip piston. There is supposed to be zero creep with a new seat, right from the start. On the older SP balanced piston regs with a knife edge piston, it takes a couple of taps on the purge, maybe a few minutes or so pressurized, to eliminate any creep.

A single dive has several hundred cycles, maybe a thousand, so this isn't about the reg not being broken in. It's either a bad seat, or my guess, that lousy brass piston. Or maybe just a really bad job of inspecting the piston edge (like not bothering to do it at all) during service.

 

[johnnywulff]

I agree we are guessing, but remember the Mk20 have change the piston from the start to late production 3 types: knife, rounded, composite this last one with the external adjust IP became the Mk25

 

[aquaursa]

It amazes me that people spend a ton of money on service and gear, but don't own a $10 IP pressure checker guage..

Fair enough. I'd say that there were several contributing factors:
1. Have never heard of this condition before
2. Have never experienced it before (have 1200 dives on my own gear)

I will certainly buy one now and use it appropriately. How often or, after what events, should one test IP? After each service, before each trip, before each dive?

Best,
Tracy

 

[halocline]

I agree we are guessing, but remember the Mk20 have change the piston from the start to late production 3 types: knife, rounded, composite this last one with the external adjust IP became the Mk25

No, the MK20 never had a knife edge piston. That ended with the MK15. It is true that there were three generations of pistons, but none of them had a sharp edge designed to cut into the seat. I also believe the composite piston was found in some of the latest MK20s, but I'm not 100% sure about that.

 

[guruboy]

No, the MK20 never had a knife edge piston. That ended with the MK15. It is true that there were three generations of pistons, but none of them had a sharp edge designed to cut into the seat. I also believe the composite piston was found in some of the latest MK20s, but I'm not 100% sure about that.

Was the stainless piston knife edge?

He agrees that the late model Mk20 had composite.