How to restore a Diaphragm First Stage with IP Creep

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macado

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picture?? I am trying to figure out what is the profile of your micromesh tip made this way, or what would be ideal shape to polish Apeks volcano.
Great work, I just got my hands on some micromesh.
IMG_20211015_145735163.jpg
 
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rsingler

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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.
 

macado

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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 pin to 21-28 lb. At some point, this will exceed the ability of the mainspring and the reg will show IP creep due to a leak past the ring where the seat meets the volcano.
Thanks! This makes a lot of sense to me. I've been fairly gentle not to flatten the volcano edge but I recognize this may only work so many more times.

I greatly appreciate your post here. It has helped me save a bunch of first tages that were flooded and deemed beyond repair
 
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rsingler

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Here's how I would dress a fixed volcano knife edge.
20220220_100114.jpg
20220220_100018.jpg

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. :wink: Sandblasted would be most any steel tank diver.
 

halocline

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Here's how I would dress a fixed volcano knife edge. View attachment 751237 View 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. :wink: Sandblasted would be most any steel tank diver.
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.
 
https://www.shearwater.com/products/teric/

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