Am I being thick?

[NotDeadYet]

... entirely possible but here goes...

I was assembling a KISS valve last night, got the cap off the top of the reg, removed the piston thingie, installed the delrin blanking disc, etc... Is it necessary? Obviously, yes or the O2 addition doesn't diminish with depth but what I mean is, can't you just lop a cm or two off the stalk on the piston rather than fitting the disc?

OK, it means sacrificing a working part but other than that it should still stop pressure being transmitted to the guts of the reg. Or, like what the title says?

[The Purist]

Same thought had crossed my mind - all you're doing is stopping ambient pressure transmitting to the diaphragm.... BUT if the crappy bit of clear plastic failed due to increasing pressure then water would flood that chamber and hit the diaphragm at ambient pressure, IP goes up and you get an extra dose of O2.

Easy enough to deal with once detected, but the delrin plug does reduce the likelihood of that failure.

[NotDeadYet]

Ahhhh, that's why it has an o-ring! I wondered about that. Cunning, those Canadians.