My Circulatory System - Explain it to me :P

[Bawls]

HELLO TFP! :fro:

We bought this house about a year ago. Previous owner had 2 pumps setup. In-between the filter and the pump pictured sat a second pump connected to 1 & 2 with rubber hoses. The pump was shot and we disconnected it and plugged 1 & 2.

About the valves:
I assume "Valve A" re-routes water through the bottleneck when closed.
When I turn "Valve B" all the way to the right(away from house) I get a consistent amount of air in the pump strainer. Opening the vent on-top of the filter will vent air for a little while then turns into a water/air mix after 30 seconds or so. Turning "Valve B" back left(towards house) removes the air and the system seems to be working as it should. There are two pipes going into the intake of the pump, the pipe with "Valve B" on it is closest to the pump.

Why do I get air when turning "Valve B" all the way to the right?
What is the bottleneck for(hour-glass shaped PVC)?
The tiny connector on said bottleneck(#3), what was that for?

Backed up to get all of it in the picture:

(Nope, that's not bird do-do on the filter top)

My skimmer has two holes, the one closest to the pool is plugged.

Thanks in advance!
I <3 me some TFP!

 

[Bama Rambler]

The extra pump going between 1& 2 was most likely a booster pump for a pressure side cleaner. #2 should be connected to the pool somewhere. The venturi #3 was for a offline chlorinator.

Now for the valves. "A" was to adjust the flow through the chlorinator as you suspected. "B" is most likely the main drain or skimmer valve.