Which of the ten are wetted
On this page15
Entirely wetted
A faucet aerator, which water passes through completely. Essentially all of its surface is in the water path.
Continuously wetted and small
A valve seat, which is the sealing face inside a valve. Small in area and permanently in contact.
Partly wetted, with a large total surface
An o ring, a supply washer and a hose washer. Each has a thin band in the water path and the rest of its surface outside.
Which is where the area weighting bites
Only the wetted band counts, so a sealing article contributes far less to the average than its size suggests.
Partly wetted, with the inside in contact
A compression ferrule, deformed onto a tube, where the bore is wetted and the outside is not.
Submerged on one side
A tank bolt, which passes through a cistern wall. A genuinely partial case and one where installation decides the answer.
Wetted at an interface
Teflon tape, compressed into a thread. Its wetted surface is whatever the joint exposes, which is thin and hard to characterize.
Not wetted at all
A pipe clip holds a pipe to a wall from outside. A push fit clip retains a fitting from outside. Neither touches water.
So two of the ten sit outside the measure
Which is a division by function and has nothing to do with the article being small or metallic.
And both are stored in the same jar as the other eight
On a shelf of 251 containers shared by nine groups, where nothing distinguishes a wetted part from a dry one.
Nothing here determines any of it
These are the ordinary functions of the ten articles, not determinations about any product or any installation.
And installation changes several of them
A tank bolt, a ferrule and a tape are all wetted to a degree that depends on how they are fitted.
Which is why the computation is per assembly
And why a component-level claim is not the same thing as a compliant assembly.
The container question is identical for all ten
Sorted, dry and findable. Which is the next section.