Im still suspect of your liq gauge, the venting would only be the air space inside the gauge from the liq to the vent which is normally on top. Often its a black rubber plug that needs to be pin punched. Most liq filled gauges will have a small decal for venting instructions. Some have a stainless pin installed into the plug which slides up and down with pressure. Either way the lower the pressure the better on all aeration pumps but especially on a vane pump.At some point when the air is calm and you have a very light rain you will see the diffuser "area of influence" as I like to call it. You should see a difference in these surface rings if you cant see a difference within the boils. You have a tremendous amount of lift so may be difficult to see a boil difference.Your valves are probably set very close regardless.
