Ok, Bill was right on the pressure being zero (except for the new Vertex diffusers having internal orifices).
Absent any internal orifices, my Matala dual diffusers read zero psi (on a 15 psi gage) and ballooned up maybe an inch. I held down one diffuser to close off the internal check valve and could tell there was no pressure then in that side, and all the air went to the other diffuser. The gage still read zero even with all the air going through the single diffuser.
So there is very little back pressure from the diffuser itself, even when out of the water absent any water head pressure. It appears according to Bill Cody's post above Vertex does put an internal restriction to force air to better equalize between diffusers when placed at different depths. This would lessen or eliminate the need for flow control valves to shut off part of the flow to a shallower diffuser (so the diffuser with the lower head pressure does not get all the flow). Probably a simplification for user who do not care to understand the dynamics of pressure and flow in their system. IE makes it more idiot proof.
Last edited by snrub; 04/29/14 08:01 PM.
