remember some pumps (this was mainly on shallow
well systems) that had a "Snifter Valve"; the purpose of which was to sniff
in a little bit of air every time the pump ran to maintain the air reserve
which is absolutely essential.

Never heard of that, and it sounds not only dumb but pointless, here is why. .
.. if you have a tank (no bladder ) 1/2 full w/ water and trapped (compressed )
air on top and your water outlet is on the bottom of the tank , HOW CAN THE AIR
ESCAPE ? ? SOOOO WHY WOULD THEY NEED TO PUT A SPHINCTER VALVE ON ? ? ?