OP
Mako1975
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What do u mean by mushy lock-up?
Scubapro MK10?
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The Mk10+ was one of the first uses of the blunt end piston and the cone seat that has become the rule today. But the piston doesn't have the mid-shaft stablilizing ring that the Mk25 and Atomics have. The only guide to closing "true" is the HP o-ring in the bore of the reg body. It may take a little polishing with a few squares of Micromesh from 4,000 to 12,000 grit to bring the blunt end smooth enough to lock up crisply. In addition, the diameter of the Mk10 piston head is much smaller than the Mk5 or Mk25. That means that the application of the relative force applied by the IP on the seat is fractionally slower, even though the end pressure on the seat is the same. It's just one more thing that makes a perfect seal harder to obtain with a simple service and seat change.
Eventually, barring a flaw in the blunt end, the cone seat will mold to the contour of the piston end and all will be well. In the meantime, there may be 5-8 psi of IP creep until it locks up completely. It may take a few hundred (thousand) cycles to get this to happen.
Part of the problem facing the blunt end piston is "sandblasting" that occurs from ?grit, ?salt crystals breaking free from the sintered metal filter at the tank end?, tank dust? that whips around the corner from the HP tank inflow down the piston shaft. It creates some minor pitting that requires polishing.
Here you can see pitting right at the point of impact, and in the second photo, more typical sandblasting, and then
a polished blunt end after a little hand work.
Eventually, barring a flaw in the blunt end, the cone seat will mold to the contour of the piston end and all will be well. In the meantime, there may be 5-8 psi of IP creep until it locks up completely. It may take a few hundred (thousand) cycles to get this to happen.
Part of the problem facing the blunt end piston is "sandblasting" that occurs from ?grit, ?salt crystals breaking free from the sintered metal filter at the tank end?, tank dust? that whips around the corner from the HP tank inflow down the piston shaft. It creates some minor pitting that requires polishing.
Here you can see pitting right at the point of impact, and in the second photo, more typical sandblasting, and then
a polished blunt end after a little hand work.
OP
Mako1975
Registered
Thanks for the advice, I will check the piston and see how it looks.
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