Question Air leaking past HP seat carrier

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Tom_Ivan

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Location
Christchurch New Zealand
Hey everyone.

I have an old unbalanced piston regulator that I think is a MK1 clone. The HP seat carrier has a hex head instead of the two holes for putting a pin spanner in.

Anyway, we've been diving on this problem free for a while when all of a sudden we started getting air leaking out the little hole that is provided for removing the seat. There is no leak if the cylinder is only cracked a little and the IP stays below about 130psi but after that we get a very big leak.
Am I correct in thinking that this is an HP seat failure and has anyone had this before? It was very sudden. Worked perfectly on one dive and failed two days later.

I've removed the seat and had a look, run my fingernail around etc to try find any damage but nothing detectible that way.

Also for interest I placed a small o ring into the carrier before placing the seat back in and repressurized it. The pressure that the leak occurred dropped down to 80psi. I think something is happening when the piston touches the seat that causes the leak.


I expect that I will have an extremely difficult time finding a replacement HP seat for this reg, especially in New Zealand. If there is anything that I could try to get this reg to seal I'd be very thankful for the suggestion.

Cheers
 
Hey everyone.

I have an old unbalanced piston regulator that I think is a MK1 clone. The HP seat carrier has a hex head instead of the two holes for putting a pin spanner in.

Anyway, we've been diving on this problem free for a while when all of a sudden we started getting air leaking out the little hole that is provided for removing the seat. There is no leak if the cylinder is only cracked a little and the IP stays below about 130psi but after that we get a very big leak.
Am I correct in thinking that this is an HP seat failure and has anyone had this before? It was very sudden. Worked perfectly on one dive and failed two days later.

I've removed the seat and had a look, run my fingernail around etc to try find any damage but nothing detectible that way.

Also for interest I placed a small o ring into the carrier before placing the seat back in and repressurized it. The pressure that the leak occurred dropped down to 80psi. I think something is happening when the piston touches the seat that causes the leak.


I expect that I will have an extremely difficult time finding a replacement HP seat for this reg, especially in New Zealand. If there is anything that I could try to get this reg to seal I'd be very thankful for the suggestion.

Cheers
Hi Tom
Pics would be a big help to try and identify what reg you have, whether it is actually a SP. SP clone... or another brand altogether.

From what you describe it could just be a HP seat o-ring that has failed or extruded if not a 90 Duro specification.
Some HP seats can be refaced using fine wet'n'dry paper with soapy water on a piece of plate glass... I've used this method with Sea Hornet HP seats in the past before I got a run of new seats CNC machined from UHDPE.
 
I have an old unbalanced piston regulator that I think is a MK1 clone. The HP seat carrier ...
These are very simple systems. (I wouldn't put an O-ring in the "carrier" if there was not one there to begin with.) Maybe there is a small crack or hole in the HP seat that you can't easily see.

If your nearby Scubapro dealer (assuming there is one) doesn't have a HP seat that will fit, I would be tempted to flip over the seat in your Mk1 to see if this will temporarily solve the problem. And then I might be tempted to "punch" a new seat out from an appropriately thick sheet of something or other (like teflon).

The seat needs to fit tight enough, I think. I wouldn't want air continuing to get "behind" the seat. I am imagining what might happen if air got trapped there, and then you ascended, and then the trapped air expanded.

Thinking out loud ...

rx7diver
 
Actually, the Mk 1 was a balanced regulator.
This is confirmed by your notation of a HP seat carrier (with a little vent hole that assists seat removal). If it were unbalanced, the seat would be in the end of the piston.
Sorry - don't know which clone has a hex removal of the HP carrier.
See this schematic:
Mk1.png

In any case, as @Fibonacci indicated, your leak is due to failure of the seal at the o-ring marked #10 in that diagram. Just replace the oring (maybe a 2-013 duro 90) and you should be fine.
A leak at the knife edge would result in IP creep which would show at the second stage when it freeflowed. A leak at the HP seat carrier o-ring (#12) might give a wet compartment on disassembly, but shouldn't show a gas leak if the seat and #11 #12 were intact.
 
Actually, the Mk 1 was a balanced regulator.
This is confirmed by your notation of a HP seat carrier (with a little vent hole that assists seat removal). If it were unbalanced, the seat would be in the end of the piston.
Sorry - don't know which clone has a hex removal of the HP carrier.
See this schematic:
View attachment 772745
In any case, as @Fibonacci indicated, your leak is due to failure of the seal at the o-ring marked #10 in that diagram. Just replace the oring (maybe a 2-013 duro 90) and you should be fine.
A leak at the knife edge would result in IP creep which would show at the second stage when it freeflowed. A leak at the HP seat carrier o-ring (#12) might give a wet compartment on disassembly, but shouldn't show a gas leak if the seat and #11 were intact.

Rob,
I am following this discussion and read your post above. In my interest to understand what you wrote, could you please explain the following a bit more?:

"...if the seat and #11 were intact."

In the exploded diagram and parts list, #11 is listed a the seat.

Also, wouldn't an issue with the seat cause the same/similar IP issue as a leak at the knife edge? Wouldn't they both result, to one degree or another, in unchecked HP air flow?

-Z
 
A leak at the HP seat carrier o-ring (#12) might give a wet compartment on disassembly, but shouldn't show a gas leak if the seat and #11 were intact.
Hmmm. Seems to me that if the O-rings #10 and #12 failed with the HP seat intact, then there would be bubbles coming out around the edge of the "carrier" (seat retainer, #13), rather than out of the tiny hole behind the HP seat.

Curious. Easy enough to run a test using one of my Mk 10's, I suppose. Maybe tomorrow.

rx7diver
 
Thanks for replies so far.

Interesting, this reg doesn't have the#10 oring from your diagram.
See pictures attachedIMG20230305163241.jpgIMG20230305163247.jpgIMG20230305163256.jpg
 

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Rob,
I am following this discussion and read your post above. In my interest to understand what you wrote, could you please explain the following a bit more?:

"...if the seat and #11 were intact."

In the exploded diagram and parts list, #11 is listed a the seat.

Also, wouldn't an issue with the seat cause the same/similar IP issue as a leak at the knife edge? Wouldn't they both result, to one degree or another, in unchecked HP air flow?

-Z
I hate it when people read what I wrote, instead of what I meant to write.
Should have been "...if the seat and #12 were intact."

And yes. Leak at the seat could be either knife edge or seat.

You're ahead of me.
 
Interesting, this reg doesn't have the#10 oring from your diagram.
Gotta have one. That's what seals the HP compartment when the valve opens (during a breath). With a #12 o-ring, the only place for IP gas to go besides your second stage is that hole in the carrier.
 
You are correct. I pulled the o-ring from my Tekna t-2100 and put it into this reg. Now all is good!

I've done about 20 dives on this reg since I acquired it. Amazing that it took this long to produce a problem! My guess is salt/corrosion around the HP seat was enough to seal it. Guess the post dive rinsing/soaking was enough to remove the corrosion and allow the air to pass around the seat.

Moral of the story: Don't rinse your regs, they need a minimum level of corrosion to work properly :eyebrow:
 

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