Mk5 Questions

[Zung]

You're right: here's a chart stolen from here (is it appropriate to steal if I quote the source?):

AL6 - .8
AL13 - 1.8
AL19 - 2.6
AL30 - 4.1
AL40 - 5.5
AL50 - 6.8
AL63 - 8.6
AL80 -10.6
AL100 - 12.4

S lp12 - 1.9
S lp20 - 3.1
S lp27 - 4.2
S lp72 - 11.9
S lp85 - 13.23
S lp95 - 14.8
S lp104- 16.2
S lp108- 16.8
S lp120- 18.7
S hp80 - 9.4
S hp100-11.9
S hp120-14.3
S hp130-15.5
S hp149-17.8

It's a bit confusing because in Europe we only use (water) capacity; tanks are filled to 200 bar except for some very old ones rated for 175 bar. The most common sizes are: 10 lt for kids, 12 lt for noobs, 15 lt for "regulars", and 18 lt or 2 x 9/10 lt for the big dogs.

 

[Couv]

.....Littly snip here, little snip there....It's a bit confusing because in Europe we only use (water) ..... The most common sizes are: 10 lt for kids, 12 lt for noobs, 15 lt for "regulars", and 18 lt or 2 x 9/10 lt for the big dogs.

Thanks for the chart, but if you only use water, why bring a tank along at all.

c

 

[Zung]

Bro, you should have your gills checked: since when can you breathe air?

 

[LeadTurn_SD]

Thread Back On Track ( ):

The rebuild parts arrived, and last night I cleaned, lubed and carefully assembled and tested the Mk5 that began this thread.... thanks again to all the usual suspects for all of the help and advice!

Observations & Lessons learned:

1.) I was very worried about safely removing the piston stem o-ring without damaging the seating surface, and approached the task with the caution of a neurosurgeon.... the patient survived. I settled on the "slip it out" using a dulled brass pick rather than "impale" using a sharp steel pick.... I'm normally an "impaler", but decided not to for this o-ring.

Note: The old piston stem o-ring was noticeably "softer" than the new "hard" replacement. I wonder if that was contributing to the high IP?

2.) I discovered that a well-lubed piston stem o-ring, when pinched just right with plastic-tipped tweezers will fly 6.5 meters into the darkest corner of the work area, and takes an average 5 minutes of searching, 6 minutes of epic swearing, and 1 beer to safely recover.

The third try was the charm, and the o-ring was installed with family-safe language.

3.) Three different "flavors" (heights) of HP seat come with the annual service kit. I chose the "medium" seat.

I used 2 of the 3 shims, positioned per instructions in this thread, and the "medium" seat.

IP is now 128 with immediate lockup, no creep, @ 3,000 psi tank pressure, but I need to test at low tank pressure still, and may end up putting the last (3rd) shim back in if IP is below 125 at low tank pressure.

Best wishes.

 

[redacted]

IP is now 128 with immediate lockup, no creep, @ 3,000 psi tank pressure, but I need to test at low tank pressure still, and may end up putting the last (3rd) shim back in if IP is below 125 at low tank pressure.

Best wishes.

I think you will be happy with 128. It might even go just a bit higher as the seat breaks in a bit more. I usually set mine on the low side even letting it drop a bit below spec at lower tank pressures.

Another recourse is to add a large washer/shim like is used in a Mk20 (01.060.219) between the body and the seat retainer. Remove the o-ring to add the shim, then reinstall. I just did that to the reg I dove yesterday and it took IP from about 121 at 400 psi to about 125. It must have been one of my Xmas regulators because it still had a bright red o-ring on the seat retainer. BTW, that same reg is 130 IP at 2800 psi with another 3 psi creep in 15 seconds. It has the old style flat seat so it might need a new seat some time in the next couple years.

 

[Zung]

...
1.)... The old piston stem o-ring was noticeably "softer" than the new "hard" replacement. I wonder if that was contributing to the high IP?

I've also found what appear to be Duro 70 o-rings in that position in previously serviced regs. I don't think it makes a big difference with the MK5/10 though.

...
2.)... takes an average 5 minutes of searching, 6 minutes of epic swearing, and 1 beer to safely recover....

You're fast. I was doing a MK20 this afternoon, and the upper bushing rolled off (not fly). I took me well over 20 minutes to recover it.

... I need to test at low tank pressure still, and may end up putting the last (3rd) shim back in if IP is below 125 at low tank pressure...

Try the halomagic: turn off the valve and purge the second stage lightly to reach whatever pressure you want.

 

[Couv]

I think you will be happy with 128. It might even go just a bit higher as the seat breaks in a bit more…..

I concur. Before you take any more action such as adding shims etc, give it a good set of cycles (25 or more.) Save gas with a device such as the one picture below:




It is a 175psi pressure relief valve. You can remove the hoses off your first stage, plug the ports except one where you screw this into. Then you could let it sit all night under pressure without worrying of a run away IP, or as I prefer. Air on, air off, pull the ring…psst 1 cycle, repeat until the wife throws something at you.

Couv

 

[redacted]

I concur. Before you take any more action such as adding shims etc, give it a good set of cycles (25 or more.) Save gas with a device such as the one picture below:



c

I tap the 2nd stage cover rapidly with the tip of my finger. I can get 1 cycle per second or better. Plus I like tools that are hard to misplace and have multiple useful applications.

 

[halocline]

I've also found what appear to be Duro 70 o-rings in that position in previously serviced regs. I don't think it makes a big difference with the MK5/10 though.

Actually it does make a big difference in the HP o-ring for MK5/10. The later regs have the bushing system to prevent extrusion, but the MK5/10 rely on the o-ring hardness.

Leadturn, an IP of 128 is perfect. These regs have great IP recovery and function perfectly well at the low end of the scale.

Edit: This thread, combined with a tiny bit of whistling from one of my MK5s, plus a healthy dose of procrastination on my part, and an upcoming dive trip, has resulted in me having a freshly rebuilt MK5 with viton o-rings throughout and a packed ambient chamber with tribolube 66. Now I have a cold water-ready O2 clean reg to dive with in the caribbean on air. You guys are a bad influence.

 

[LeadTurn_SD]

...Try the halomagic: turn off the valve and purge the second stage lightly to reach whatever pressure you want.

Very good idea. Thanks (to both of you ).

I'll test at low pressure per the above advice, and assuming the IP stays within "spec" I'll leave it alone.

Now I need to clean and tune the R109 that came with the Mk5

I see an order to McMaster-Carr in my future (to stock up on o-rings); I was surprised the annual kit only came with the "must change" dynamic o-rings.... in my case, no biggie, since all the static o-rings were in good shape and I just reused them.

Other brands often include all the o-rings, since they are so cheap.... but I could see that a dealer would probably have the various static o-rings in stock, where as the DIY'er may not.

Best wishes.