Operations Questions: SP MKV / 108 (not really vintage but not plastic either)

[george_austin]

[h=3]Operations Questions: SP MKV / 108[/h]Sun Aug 02, 2015 2:19 pm
So 1 year ago I installed the SP 108 service packs from VDH on my SP 108's and used the instructions to replace the soft seat and the O rings for the second stage, downstream valve, set the adjustable orifice / downstream valve as directed via the SP instruction data sheet. The MK V was just rebuilt 2 years ago but not used - stored in a plastic bag in a cool basement year round.

Yesterday I was setting up my rig that will be in pool sessions with dive prospects and other new divers - BP/W / MK V / 108 and just did some routine leak checks and checked the IP - IP locked on a 2,100 psi tank at 145 psi with no creep observed after 15 minutes under pressure- cycled purge valve on primary and octo (SP108 also) - looked fine.

Last night I went to Fisherman's Cove / Mermaid Grotto in Laguna Beach, CA. for a solo night dive.
Dive depth 32fsw X 62 minutes.
Started dive with 2100 psi
Ended dive with 200 psi
Vis. 10 ft / surgy at 20 ft and above
First dive since first / second stage service!
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Conditions:
The regulator delivered plenty of air from full tank to nearly MT but at times the air delivery was noticeably , well, "urgent" and seemed to "surge". This condition happened infrequently at varying tank pressures throughout the dive and seemed to be a little more noticeable in a head up position while inspecting the wall/reef. The surgy air delivery happened maybe 3 or 4 times total but was a little alarming as I have been diving nothing but my PRAM for the past 100 or so dives and have grown accustomed to its smooth delivery despite varying tank pressures and exertion levels in currents and what not.

Upon returning home I checked the IP on the reg and the same tank - (200 psi post dive) and the IP is a rock solid 125 psi.
I'm thinking I may have a downstream valve on the SP 108 slightly too hot?
Should I back out 1/8 of a turn? - Detune
The regulator does not hiss at all when connected to a full tank and pressurized, I might add.
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The conditions noted that I dislike are -
1.) Inhalation effort is a little too sensitive for my taste - the regulator feels "too anxious" to deliver the next breath
2.) The infrequent, surgy, almost "explosive" nature of the air delivery even with a tank pressure of 300 psi or even 200 psi.
3.) Since the first stage is coupled to the tank which is mated to a "tec" style BP, I feel that the tank strap slots push everything up too high or more accurately, bring the BP lower on the ST72 cylinder. - yes, I can easily reach my cylinder valve but I'm not always in a GUE style horizontal trip and I am annoyed by being able to snap my head back and feel that the first stage is too high.
4.) I can hear the first stage working during breathing cycles during the dive - I hate that.
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Anyway, I am wholly unfamiliar with the MK V / 108 and its peculiarities - I understand the operational characteristics of the flow thru balanced piston design and how the downstream valve is intended to work however.
Maybe I'm just comparing apples to oranges WRT the PRAM and the MK V / 108.
Gimme back my double hose!! (not allowed with students in pool or open water)
Anyone have any thoughts?
Thanks,

 

[redacted]

I would be mildly concerned with what is going on with your Mk5. It should not be an IP of 145 on one day and 125 on another with no intervention. I like 125, but I would monitor it closely.

You might want to consider replacing that 108 with a 109 to get more control. But, it seems to me like the 108 is working pretty well. It costs nothing to try a slight de-tune.

 

[scubafanatic]

Like awap, I went with 109s instead of 108s to get 'in the field' control offered by the 2nd stage adjustment knob. Also, as previously mentioned, 1st stage IP should be pretty stable, def not randomly swinging by 20 psi ! I'm not a reg expert, but have learned a lot over the last approx 18 months as I've acquired enough Mk 5's and 109/156's to build over a dozen complete reg sets (I should have a total of 8 complete sets dive ready by end of this month). I know how to tune the 2nd stage cracking effort, the actual rebuilding/upgrading duties I leave to veterans like 'couv' and Bryan @ VDH, so you might consider contacting them for examination/service.

 

[george_austin]

Thanks
The IP was rock steady with a full tank but post dive it was at 125 psi with only 200 psi tank pressure so I think this is a normal drop on a first stage connected to a near empty tank. There's reall no point in checking IP on first stage when it's connected to a tank with only 200 psi - it's really not giving me any useful feedback with a tank pressure below 400 or so - am I wrong?
As well, after revisiting my Scubapro specs, I see that they call for between 2-3 inches of water for cracking pressure on the 108/109 and my primary was 1.75 inch - that's too light for surgy beach condition diving with hanging out at 15 ft with 2 ft swells passing overhead. I'm thinking, obviously, refill that tank, recheck IP to repeat normal IP number of 145 psi and bring a little more spring force to bear on the back side of diaphragm by turning in downstream orifice CW by 1/8 turn - then recheck cracking pressure - supposed to be between 0.072-0.108 not 0.063 which is what I have now. I like the relatively neutral way the reg feels in my mouth although the closest fitting mouthpiece I can find is still just a tad loose so the brass body breaths wet plus a not great seal at the mouthpiece is making it wetter. Not a big issue.
My initial root cause for the surge last night is pretty much a reg with too light cracking, and surgy beach diving conditions.
Yes, a properly set up 109 with diver adjustment would have been nice.

The MK5 is pretty amazing though - delivers the same air at 2100 tank psi or 200 - me like that.

Has anyone even done monitoring of their IP during the entire course of a dive? Full tank to empty, drifting to finning really hard against a current - etc

 

[redacted]

Thanks
The IP was rock steady with a full tank but post dive it was at 125 psi with only 200 psi tank pressure so I think this is a normal drop on a first stage connected to a near empty tank. There's reall no point in checking IP on first stage when it's connected to a tank with only 200 psi - it's really not giving me any useful feedback with a tank pressure below 400 or so - am I wrong?
As well, after revisiting my Scubapro specs, I see that they call for between 2-3 inches of water for cracking pressure on the 108/109 and my primary was 1.75 inch - that's too light for surgy beach condition diving with hanging out at 15 ft with 2 ft swells passing overhead. I'm thinking, obviously, refill that tank, recheck IP to repeat normal IP number of 145 psi and bring a little more spring force to bear on the back side of diaphragm by turning in downstream orifice CW by 1/8 turn - then recheck cracking pressure - supposed to be between 0.072-0.108 not 0.063 which is what I have now. I like the relatively neutral way the reg feels in my mouth although the closest fitting mouthpiece I can find is still just a tad loose so the brass body breaths wet plus a not great seal at the mouthpiece is making it wetter. Not a big issue.
My initial root cause for the surge last night is pretty much a reg with too light cracking, and surgy beach diving conditions.
Yes, a properly set up 109 with diver adjustment would have been nice.

The MK5 is pretty amazing though - delivers the same air at 2100 tank psi or 200 - me like that.

In a perfectly balanced 1st stage IP will not change with tank pressure until that pressure falls below IP. My Mk5s can present quite a bit of swing but rarely as much as you are seeing. I believe the biggest contributor is HP piston o-ring friction. You might want to check the HP piston o-ring and make sure it is duro 90. When I get a lot of swing, I go to a urethane duro 90 with lots of lube which seems to help a bit.

I like an adjustable 2nd when I have to deal with surge and current. Your referenced spec seems too high. A good 2nd should work well at 1.2 to 1.5". I take my adjustables below that and control with the user adjustment.

 

[george_austin]

Good, ok - thanks

 

[scubafanatic]

Thanks
The IP was rock steady with a full tank but post dive it was at 125 psi with only 200 psi tank pressure so I think this is a normal drop on a first stage connected to a near empty tank. There's reall no point in checking IP on first stage when it's connected to a tank with only 200 psi - it's really not giving me any useful feedback with a tank pressure below 400 or so - am I wrong?
As well, after revisiting my Scubapro specs, I see that they call for between 2-3 inches of water for cracking pressure on the 108/109 and my primary was 1.75 inch - that's too light for surgy beach condition diving with hanging out at 15 ft with 2 ft swells passing overhead. I'm thinking, obviously, refill that tank, recheck IP to repeat normal IP number of 145 psi and bring a little more spring force to bear on the back side of diaphragm by turning in downstream orifice CW by 1/8 turn - then recheck cracking pressure - supposed to be between 0.072-0.108 not 0.063 which is what I have now. I like the relatively neutral way the reg feels in my mouth although the closest fitting mouthpiece I can find is still just a tad loose so the brass body breaths wet plus a not great seal at the mouthpiece is making it wetter. Not a big issue.
My initial root cause for the surge last night is pretty much a reg with too light cracking, and surgy beach diving conditions.
Yes, a properly set up 109 with diver adjustment would have been nice.

The MK5 is pretty amazing though - delivers the same air at 2100 tank psi or 200 - me like that.

Has anyone even done monitoring of their IP during the entire course of a dive? Full tank to empty, drifting to finning really hard against a current - etc

I can 100% confirm the following 3 mouthpieces will fit the 109/156 tightly:

Seacure 1
OEM Atomic Aquatics mouthpiece (these run $ 14.00 each) https://www.divegearexpress.com/atomic-mouthpiece-kit-gray-black-oem
Diverite mouthpiece: these run $ 4.00 each) https://www.divegearexpress.com/c-bite-mouthpiece

 

[george_austin]

Great - thanks for the mouthpiece info - I like the guys at DGX - great customer service and prices

 

[Couv]

Hi George Austin,

If I'm reading the symptoms correctly, it sounds like something is binding in the second stage. But before we go any further, let's properly troublehoot this thing. First, isolate the problem to the first or second (possibly both) stage. Remove the 108 from the MK V put a "known good" second stage in it's place and test it. Does the problem still exist? If so, Master Awap has probably nailed it. The piston stem o-ring might very well be extruding. Put in a good hard 90 duro o-ring, make sure the piston itself has not glazed where it interfaces with the o-ring. If it has, take some Scotch Bright and rough it up a little. HEAVY on the lube in that area.

Do the same with the 108. Hook it up to your PRAM and breathe it in a similar fashion as you were when you noticed the issue while diving. Has the problem followed the second stage? If so, remove the cover and diaphragm. Exercise the lever. Any binding noticed? Perhaps the seat carrier, lever feet, or something else if binding. Check the spring to make sure it isn't broken. One issue I've seen a few times with a regulator that age is on the metal diaphragm disk itself. The metal lever rubs striations into the disk and causes the lever to hang up and then skip. You can replace the diaphragm, turn it 90 degrees to the position that it's in, or polish out the striations.

But again, first isolate the problem.....it might be something simple like sand getting into the second stage.

Good luck and keep us posted.

Couv

 

[george_austin]

Thanks, couv - I suppose testing as written above likely ought not be done on a 110 ft wreck dive next weekend? - I guess I'll do another local night beach dive this week or hell, if I go early before the lifeguards show up, I can do a solo dive. anyway -

I refilled that tank and retested the Mk5 IP and it went straight to 145 again, rebounds immediately after a cycle. I set cracking pressure to .072. I have a great little Swimmaster MR12 that I think I got from you? I can use that for the testing - also some Conshelf XIV seconds. The Swimmaster is the talk of the dive boats here sometimes as I call it a Harley Davidson (AMF / Harley, get it?) Thanks all for the input.