fmerkel
Contributor
Fine bubbles coming out of the wife's MK20, time for the yearly anyway so I opened it up. Pretty much everything normal except the Piston O-ring was breaking down with some missing pieces. I think I found one on the Octo seal. It leaked and would not 'adjust' so I pulled that apart and found a flattened black fleck stuck to the surface. Fine after I flicked that off.
O-ring, hose lining, some other crud?
So, this is the 2nd piston O-ring to break down on me. These are Scubapro out of a stock kit. I have been inserting the piston without the bullet but I've been doing that for years and this is the first time I've had problems. I DID order up the Mark 20 Assembly tool and Piston Bullet from [scubatools].
While waiting for that to arrive I found a Viton O-ring of the right size for the piston (feels by fingernail to be a tad more 'squishy' than the stock), and put it together having changed nothing but the O-ring. No leaks, kind of a mushy IP lock starting at 135 and drifting up to 145. Pulled a shim, IP dropped to 125 and the IP got even mushier.
Swapped out the Piston (old seat mind you), and the IP kept creeping until the 2nd stage would start burping. Put the shim back in and got the same result, but at a higher IP.
Put in an old 'retired' piston I had marked as having this kind of creep problem....but, I had worked the edged with 1000 > 2000 grit wet and dry.
Wham! Immediate decent lock.
Looking at all the piston edges with a +5 magnifier and a jewelers loupe I can't tell any real difference.
The questions are:
1. Why is the O-ring shredding?
2. If the Viton O-ring is working is it reasonable to use it? I certainly don't have to as I have kit replacements.
3. Why is this damn thing so difficult about locking the IP? I have a bunch of different regs, piston and diaphragm from many manufacturers and this one is a real pain that way. But my wife loves it, so I keep it going.
Kind of long winded. Thanks in advance.
O-ring, hose lining, some other crud?
So, this is the 2nd piston O-ring to break down on me. These are Scubapro out of a stock kit. I have been inserting the piston without the bullet but I've been doing that for years and this is the first time I've had problems. I DID order up the Mark 20 Assembly tool and Piston Bullet from [scubatools].
While waiting for that to arrive I found a Viton O-ring of the right size for the piston (feels by fingernail to be a tad more 'squishy' than the stock), and put it together having changed nothing but the O-ring. No leaks, kind of a mushy IP lock starting at 135 and drifting up to 145. Pulled a shim, IP dropped to 125 and the IP got even mushier.
Swapped out the Piston (old seat mind you), and the IP kept creeping until the 2nd stage would start burping. Put the shim back in and got the same result, but at a higher IP.
Put in an old 'retired' piston I had marked as having this kind of creep problem....but, I had worked the edged with 1000 > 2000 grit wet and dry.
Wham! Immediate decent lock.
Looking at all the piston edges with a +5 magnifier and a jewelers loupe I can't tell any real difference.
The questions are:
1. Why is the O-ring shredding?
2. If the Viton O-ring is working is it reasonable to use it? I certainly don't have to as I have kit replacements.
3. Why is this damn thing so difficult about locking the IP? I have a bunch of different regs, piston and diaphragm from many manufacturers and this one is a real pain that way. But my wife loves it, so I keep it going.
Kind of long winded. Thanks in advance.