Air shooting through holes on HP seat retainer of MK7

[Reefer]

Recently brought a nice MK7 from ebay.
Initial test with 800 psi tank showed 153psi IP. All internal parts looked great except a piston where grease are mixed with green rusts. Surprisingly there was no shim for spring. Had hard time to take HP seat out from retainer. had no luck with forcing with air pressure from back side of retainer so used drill bit to take it carefully out. I was not sure if HP seat was glued.

So I cleaned, changed all o-rings and HP seat with a service kit from VDH and tested with tank with 800 psi. All looked great but IP was a bit high around 130 with one shim that I put between Spring and main housing. I just wanted to have a shim there.
Yesterday I tested that MK7 with 2800 psi tank. looked good with 135 IP until I depressed purge on 2nd, I heard bang! and there was air shooting through holes on HP retainer mainly one in center and had to close main valve to stop that.
I didn't thight HP seat retiner with a tool, just with my hand as much as I could, like a couple of other 1st I serviced. A HP seat retainer tool I made is very small one like one from Herman so there is not much leverage.
Will try to tight retainer tonight but are there any other things I have to take a look?

 

[rx7diver]

Reefer,

It's been a long time since I last serviced a Mk7, but I seem to recall that the only way air can escape from the HP seat retainer is either (1) from around the HP O-ring that seals the retainer (which can happen in the O-ring fails), or (2) through the center hole (that's used for removing the HP seat).

If the HP seat is defective and somehow broke apart or became partially unseated when you pressurized the reg, then you could have air escape through the center hole of the HP seat retainer.

If the intermediate pressure is too high, is it possible that the piston's knife edge can cut completely through the HP seat? (I don't really know. Maybe someone else can comment about this.)

I think that what is more likely is, you either installed a defective HP O-ring on the HP seat retainer, or you somehow pinched the HP O-ring when you were screwing in the HP seat retainer, or you didn't tighten enough the HP seat retainer when you screwed it in—and, in either case, the HP O-ring on the HP seat retainer blew. Can you check this?

BTW, iirc, an intermediate pressure of 130 psig isn't too high for a Mk7.

Also, a shim is in itself NOT necessary. If the intermediate pressure falls within spec without it, it is not necessary.

Let me repeat, it's been a *very* long time (>10 years?) since I last serviced a Mk7, so my memory might be getting things confused. And I am NOT a certified Scubapro tech.

Safe Diving,

rx7diver

 

[redacted]

I'm about 99.99% sure your problem is the o-ring that seals between the body, the seat retainer, and the seat was not seated well during assembly and has popped out of place. It probably was a purple o-ring when you disassembled it and is a -013 duro 70 if you need to get another. But that o-ring can probably be re-installed with no problem. The trick is it must be seated correctly in the groove in the body before you install the seat retainer. You can't just lay it in position or even get away with just pushing it in with your finger. I drop it into place, push it in a bit with my finger, and then use a socket with an outer diameter of about 9/16 inch and use it to push and rock the o-ring into the groove.

This is a problem that actually caused scubapro to replace the o-ring they used for so many years with a red washer that would seat without being pushed into place at first. There techs were having enough trouble that they made the design change. I got a Mk5 from a shop that had that problem and could not fix it. They declared the reg unservicable and I ended up with it. Sure enough, the o-ring was out of place and I installed it correctly and all is fine.

If you continue to have a problem, let me know and we can see what else might be done.

I'm not sure why air did not blow the old seat out. Did you use an air nozzle off an LP hose held tightly against the retainer? I have never had one effectively resist and I have had quite a few fly across the room when I did not have my hand positioned to catch them. But deal with that next time (5+/- years from now). At this point you do not want to disturb the HP seat in the seat retainer unless you intend to replace it.

130 psi on an 800 psi tank does not sound bad but I don't like to go much higher than that. A full tank may take that up into the 135 to 140 range. If you ever need to remove that piston for any reason, I'd consider removing the single washer. But I like to set IP fairly low and leave it room to grow over an expected 3 to 5 years of use.

I have seen HP seat failure in that design but that was from some old material seats that are gone now. If the seat fails, IP control is lost and there would be gas coming out of downstream valves. Your seat should be fine. I use bent nose needle nose pliers to tighten that seat retainer but you could get away with a single finishing nail to torque it into place. Finger tight is probably not enough which may have contributed to the original problem. Do reseat that o-ring before you try to tighten the retainer, although I doubt if you could hurt it..

Let me know if I can help. Good Luck

 

[Reefer]

rx7diver and awap,

You were right about the O-ring on top of HP seat retainer.

Opened the retainer and found the o-ring damaged probably due to misplacement. The groove (step) for the o-ring was very shallow so couldn't see well unlike my MK5 (all parts are latest except turret retainer being brass) which has very obvious clear step for that particular o-ring. Put an original old O-ring since I didn't have a -013 on hands (New ones are on the way) as precise as I could and tested. bang! this time I even didn't depress the purge on 2nd. Opend again and O-ring was not damaged. Put the o-ring back again to where I guess it should be. This time, I applied some lube at around the edge of the HP seat where it supposed to touch the o-ring to minimize friction between the o-ring and seat while retainer was being screwed in. Just in case the friction caused misplacement. Tested. Everything worked as it should! had creeping around 3-4 psi this time not sure why but could be retainer tightened more than before. Will open again and change the O-ring and HP seat to new ones once I get new o-rings.

Regarding original old HP seat, it was reddish clear color cone shaped and was very tight in the retainer.

I have a plan to use this MK7 as my main 1st. I have very nice MK25/S600 set up but want to use wireless transmitter and my old Air2 2nd G so I can remove SPG and Octo. MK7 should give me redundancy for tank pressure since I don't trust transmitter 100% with only two hoses attached.

Thank you for helpful advices. Wouldn't be able to solve the puzzle without you.

Reefer

 

[redacted]

My experience is the honk is not really reliable. It tends not to occur until under 400 psi and may not occur at all if you are a light breather. But there is one last warning. When tank pressure falls below IP the oscillator seats and lets very little gas by - not enough to breath. At that point you must switch to your alternate where you should have a few breaths left (about a spare air's worth).

 

[Reefer]

My experience is the honk is not really reliable. It tends not to occur until under 400 psi and may not occur at all if you are a light breather. But there is one last warning. When tank pressure falls below IP the oscillator seats and lets very little gas by - not enough to breath. At that point you must switch to your alternate where you should have a few breaths left (about a spare air's worth).

MK25/S600 is very good regulator. Too good so I didn't notice anything even with very low pressure in tank. I also like to have some inhale resistance so I don't care much about low cracking pressure but maybe it's just only me. It is nice that MK7 can give me two warnings or at least one hard one. it's much better than having last breath full and easy and nothing. only drawback is it's weight for me.

Reefer

 

[rx7diver]

MK25/S600 is very good regulator. Too good so I didn't notice anything even with very low pressure in tank. I also like to have some inhale resistance so I don't care much about low cracking pressure but maybe it's just only me. It is nice that MK7 can give me two warnings or at least one hard one. it's much better than having last breath full and easy and nothing. only drawback is it's weight for me.

Reefer

The instructor for my university open water course (in 1986) was also a Scubapro dealer. He used to sell quite a few Mk 7's to his certies, especially those who dove in farm and otherwise extremely muddy ponds/lakes. For this "black water" diving, he preferred—and recommended—diving with a Mk7 rather than with a J-valve tank valve. Several of my friends bought Mk7's, and I got plenty of experience servicing their Mk7's.

I mentioned once when i was TA-ing, that I'd like to learn to service regulators. The instructor handed me a stack of schematics and a bunch of the course's Mk5's and Adjustables and Balanced Adjustables that needed attention. Basically, I sat at a table poolside repairing regulators when he was teaching the wet sessions. He would wander by occasionally to check my progress and give me pointers. An excellent learning experience! Eventually the TA's and assistant instructors started bringing their personal Mk5's, Mk7's, and Mk10's to me for servicing, which I was always happy to do.

I developed a special love for the Mk7. It's such a delightful brute! Enjoy it!

Safe Diving,

rx7diver

P.S. I was a graduate student at the time, and on my own dime, so I couldn't afford the Mk7 that my fellow students' parents purchased for them. Instead, I purchased a Mk10 and never looked back! I still own and dive this Mk10, my first regulator. Still love it!

 

[Reefer]

Got new -013 V90 O-rings so replaced original -013 (pupple?) carefully with new -013 V90 and tested. Bang!
Opened retainer and found the O-ring was slightly scratched. replaced with New -013 V90. I was pretty sure O-ring was sit correctly. and Bang. again.
I started to scratch head and thinking possible problems.

A. Seat is not proper one.
I was using Trident HP seat that replaced semi transparent one which was in the MK 7 when I got it.If you see attached picture (1. Old flat seat from MK10, 2. original seat came with the MK7, 3. Cone Seat from MK10, 4. Trident Seat currently installed) Height of the seats are different and I believe the -013 Oring sits between housing and on top of the seat? How this possible to use both flat and new seat in same regulator?
I put seat (1) in the retainer and found belows.
a. Top of crown of retainer flush with flat seat(1) but slightly lower with others when seat was installed.
b. I actually could feel different force when I tighten retainer with 1 compare to with 4
c. after installing seat(1) to MK7, No Bang so far. but IP was creeping to 160 where I closed valve probably due to seat was from MK10.

B. Top edge of the crown of retainer has bad scratches around it
C. Wrong Retainer
Maybe when it serviced last time it was replaced with wrong one?

I don't think I will dive with this MK7 unless I find real root cause. I don't have another retainer or new flat seat to test with on hand. I'm kinda lost here.

Reefer

 

[halocline]

The seat is not your problem, it's the seal of the o-ring. It's just a bad spot; it's very tricky to get that 013 in place, and tiny differences in particular o-rings can cause a leak. It doesn't take much.

The best thing for you would be to get one of the red bushings that come with the current MK5/7/10 kits. Toss the o-ring and use the bushing, it will work fine. If you don't have access to one of those kits, get a few different 013 o-rings; 70 duro, 90 duro, EPDM, nitrile, maybe even a polyurethane. One of them will hopefully fit correctly and work fine. One caveat, you mentioned the crown of the seat retainer is scratched. If you're talking about a surface that the o-ring is supposed to seal against, that could be a problem. You might need a new retainer. But I've never seen one scratched enough in the right spot to actually leak.

The kits come with 3 seats of varying heights. Because your IP is a bit high and you want to use shims (I don't know why, personally I would rather not use any shims), try the highest profile seat, it will set your IP lower.

 

[redacted]

Got new -013 V90 O-rings so replaced original -013 (pupple?) carefully with new -013 V90 and tested. Bang!
Opened retainer and found the O-ring was slightly scratched. replaced with New -013 V90. I was pretty sure O-ring was sit correctly. and Bang. again.
I started to scratch head and thinking possible problems.

A. Seat is not proper one.
I was using Trident HP seat that replaced semi transparent one which was in the MK 7 when I got it.If you see attached picture (1. Old flat seat from MK10, 2. original seat came with the MK7, 3. Cone Seat from MK10, 4. Trident Seat currently installed) Height of the seats are different and I believe the -013 Oring sits between housing and on top of the seat? How this possible to use both flat and new seat in same regulator?
I put seat (1) in the retainer and found belows.
a. Top of crown of retainer flush with flat seat(1) but slightly lower with others when seat was installed.
b. I actually could feel different force when I tighten retainer with 1 compare to with 4
c. after installing seat(1) to MK7, No Bang so far. but IP was creeping to 160 where I closed valve probably due to seat was from MK10.

B. Top edge of the crown of retainer has bad scratches around it
C. Wrong Retainer
Maybe when it serviced last time it was replaced with wrong one?

I don't think I will dive with this MK7 unless I find real root cause. I don't have another retainer or new flat seat to test with on hand. I'm kinda lost here.

Reefer

A duro 90 o-ring is harder than the original o-ring and may not seal as well. You should use a duro 70. And it must be seated correctly to work reliably. That means the o-ring must be fully seated in the groove before the retainer is installed. Pushing it in with your finger is not reliable.

the problem is that if the o-ring is not seated properly, HP gas may seep by it into the area of the retainer threads resulting in HP gas in the inlet chamber where it belongs and in the area between the seat retainer o-ring and the HP seat o-ring. When the reg is cycled, the gas pressure in the HP chamber drops and the errant pressure between the above 2 o-rings dislodged the HP seat o-ring. The design does not accommodate that pressure imbalance.

The seat retainer in the Mk7 is the same part as in the Mk5 and the Mk10. If you are concerned about the integrity of your Mk7 seat retainer, you can try one from any of the compatible models. (The various HP seats are also compatible from one model to another.)

That pictured seat #1 has a very large groove and I would not expect it to hold IP very well. If the other side of that seat is unused, that flat seat may be flipped providing a new sealing surface.

I can't see any significant difference in the height of your pictured seat. Total height is not ther issue as the will differ by the design of the "cave cone". the height that matter is from the bottom of the seat to the top edge where the o-ring must provide a seal. I have played with that seat height as another means of adjusting IP and smaller differences do not compromise the seal between the seat and the seat retainer, so I doubt if that is your problem. You might also want to take a close look at the gland in the body where the O-ri8ng must sit. Scratches in that gland could allow gas to seep behind the o-ring and such a problem would be more sever with a duro 90 o-ring than with a duro 70. The softer duro 70 would tend to seal such scratches better.

Good luck.