Ok guys here is this first installment on how I make HP seats, lets start with the flow by piston regulator HP seats, they are easiest to do. Please forgive my somewhat out of focus shots, using super macro with a bunch of added diopters makes focus a little touchy. The material I am using is "Extruded Plastic NATURAL Round Teflon Virgin ". The material is listed as having a diameter of 0.1875 but my piece is 0.186 diameter (measured). It comes in pretty much any length you want but I ordered 3 ft of it, it's cheap so why not. According to the vendor it has a hardness of 50 durometer. I originally tried nylon and found it to be too hard. The teflon cuts and sands easily so working with it is fairly easy. You guys that have Scubapro MK-2s are lucky. I measured the diameter of the original seats as 0.184 but the material is soft enough that it fits snuggly as is so no size reduction is necessary- or at least with the piece I have YRMV. For USD regs the diameter needs to be reduced to 0.180. This can be done with either a lathe or if you are careful and work with a short length you can sand it down while spinning it in a drill press. Making the seats themselves for any flowby piston reg (Mk-2, Sherwoods, USD Aquarius and a ton of others) is the same process
The material can be bought at Online metals , here is a link.
Order Plastic Teflon Round in Small Quantities at OnlineMetals.com
I have ordered from these folks seveal times, always fast and friendly so no complaints about them.
I started by making a cutting jig. This is nothing more than a 0.185 hole bored into an aluminum block. The other holes are for other projects, the HP seats for SP MK-2 just uses the hole the teflon is in. Steel or most any other metal will do but I would not suggest any type of plastic. This holds the stock while you cut it to length. The hole is slightly smaller than the stock but it seems to fit nicely, very snug but reasonably easy to move. Here is a photo of the cutting block with the stock inserted, the remaining stock (several feet of it) is hanging out the back side of the block.
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I first trim off little sliver of the material to square it up. This is done with a single edge razor blade. Thin slivers are best and give you a more flat cut. Doing 2 or 3 cuts to get the seat flat is better than trying to do it all at once. You don't need to remove much material, just enough to get the surface flat.
Then I move the stock up to a thickness that is slightly greater than the thickness of the finished seat, for MK-2s the seat is 0.127 so I go up to 0.135 or so, the amount is not critical but too much is harder to trim accurately.
Next I cut off the new seat with the single edge razor, keeping it as flat as possible.
Now install the new seat with the original cut (flattened- sliver removed ) side inside the piston. If possible it’s a good idea to use an old piston for the next step but if done carefully this step will not damage a good piston. With the seat firmly seated in the piston, use the single edge razor to trim the seat flush with the top of the piston. Again, the objective is to only cut off a thin sliver, the thinner it is the better your seat will be.
And the finished product installed in a piston.
This old Mk-2 locked up quickly and after a dozen or so cycles it seems to be working nicely. I watched the IP over an hour and so far it has not moved at all. I have had a similar HP seat installed in an old USD Aquarius for a week, it has locked up solid and seems to work well, you just have to reduce the size of the stock to get it to fit. The procedure to make HP seats for any flow by piston reg is going to be the same, just different diameters.
I also have been working on a HP seats for flow thru piston regs like the SP MK-5, it's clones and one for another reg similar to the MK-5. I have no idea who made it, it has no marking but it's a nice compact little reg very similar to the MK-5. If you guys want I will do a similar thing for them but it may take me a little while, I am going diving.
