How to restore a Diaphragm First Stage with IP Creep
- Thread starter rsingler
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
OP
Keep in mind that avoiding IP creep is a function of the seal (obvious), which with a hard seat is a function of the contact area (not so obvious).
Work with me on the next, because there's maths.
This circle might be 0.15" in diameter, and the sharp knife edge produces a contact ring of say, 0.012" in width.
Circumference of a 0.15" circle = 0.15 x 3.142, or
0.39 inches.
Area of contact is therefore 0.39 x 0.012, or
0.0046 sq in. For tank pressure of 3000psi to not leak past this seal (assuming it's perfect) there must be at least 3000 x .0046, or 14 lb of force on the seat.
If you dress the volcano flat on, against a somewhat flexible base (pencil eraser), you begin to dull the edge of the volcano. This then widens the circle of contact with the seat, and thus the area of contact. It is VERY easy to flatten the volcano to the point that you increase the circle of contact's width by 50-100%.
This may change the required force on the seat to 21-28 lb. At some point, this will exceed the ability of the mainspring to apply enough pressure to seal, and the reg will show IP creep due to a leak past the ring where the seat meets the volcano.
For example, I can adjust my old shop Conshelf 14 from its usual of 135 psi, to 180 psi to drive a specialty piece of equipment. But I can't get more than that before the spring adjuster bottoms out. That means I get a max of 33% increase in spring pressure. If I polish the volcano of a leaky eBay Conshelf that I got for $35, so I can dive with it, I can't dull the line of contact of that volcano by more than 33%.
This over-long discussion is a complex way of saying that dressing flat on (as opposed to polishing with a thin cone of Micromesh that also removes metal from the interior of the volcano), limits you to only a couple of restorations before the volcano is too dull to seal.
And polishing with a cone deep inside the body of a fixed volcano reg (as opposed to one whose orifice is removable) is a real PITA.
Congrats to @macado for sharing a great technique for restoring a diaphragm reg! Know only that you need to be fairly gentle in your efforts.
Work with me on the next, because there's maths.
This circle might be 0.15" in diameter, and the sharp knife edge produces a contact ring of say, 0.012" in width.
Circumference of a 0.15" circle = 0.15 x 3.142, or
0.39 inches.
Area of contact is therefore 0.39 x 0.012, or
0.0046 sq in. For tank pressure of 3000psi to not leak past this seal (assuming it's perfect) there must be at least 3000 x .0046, or 14 lb of force on the seat.
If you dress the volcano flat on, against a somewhat flexible base (pencil eraser), you begin to dull the edge of the volcano. This then widens the circle of contact with the seat, and thus the area of contact. It is VERY easy to flatten the volcano to the point that you increase the circle of contact's width by 50-100%.
This may change the required force on the seat to 21-28 lb. At some point, this will exceed the ability of the mainspring to apply enough pressure to seal, and the reg will show IP creep due to a leak past the ring where the seat meets the volcano.
For example, I can adjust my old shop Conshelf 14 from its usual of 135 psi, to 180 psi to drive a specialty piece of equipment. But I can't get more than that before the spring adjuster bottoms out. That means I get a max of 33% increase in spring pressure. If I polish the volcano of a leaky eBay Conshelf that I got for $35, so I can dive with it, I can't dull the line of contact of that volcano by more than 33%.
This over-long discussion is a complex way of saying that dressing flat on (as opposed to polishing with a thin cone of Micromesh that also removes metal from the interior of the volcano), limits you to only a couple of restorations before the volcano is too dull to seal.
And polishing with a cone deep inside the body of a fixed volcano reg (as opposed to one whose orifice is removable) is a real PITA.
Congrats to @macado for sharing a great technique for restoring a diaphragm reg! Know only that you need to be fairly gentle in your efforts.
OP
Here's how I would dress a fixed volcano knife edge.
As I suggested above, a PITA. Lots of shifting and retaping of the Micromesh to bring fresh paper to bear on the volcano. May take 20 min or more. But it beats discarding the reg body if the volcano has gotten dinged or sandblasted. "Dinged" would be an eBay reg serviced before by some other technician.
Sandblasted would be most any steel tank diver.
As I suggested above, a PITA. Lots of shifting and retaping of the Micromesh to bring fresh paper to bear on the volcano. May take 20 min or more. But it beats discarding the reg body if the volcano has gotten dinged or sandblasted. "Dinged" would be an eBay reg serviced before by some other technician.
Sandblasted would be most any steel tank diver.halocline
Contributor
That's how I would do it too, if I had any diaphragm regs to work on (I might have one conshelf left someplace). But I use the same sort of technique with pistons and I've even cleaned up a 2nd stage orifice or two like this. It works fine; you're not grinding a new edge, just honing and cleaning.Here's how I would dress a fixed volcano knife edge.View attachment 751237View attachment 751238
As I suggested above, a PITA. Lots of shifting and retaping of the Micromesh to bring fresh paper to bear on the volcano. May take 20 min or more. But it beats discarding the reg body if the volcano has gotten dinged or sandblasted. "Dinged" would be an eBay reg serviced before by some other technician.
Similar threads
