use of main drain with skimmer float

[Manslick]

http://www.poolsinc.com/jacuzzi-mode...s-skimmer.html

This may help.

[byron366]

this picture does describe my skimmer, but it still doesn't show how the part works.. i think that it must be the weir or something, but i don't know how it works

[mas985]

Restricting either the skimmer or main drain side reduces efficiency so I would leave both the skimmer and main drain fully open (i.e. remove the flap all together on the float and main drain port). This will result in the lowest head loss possible and the highest flow rates. This will usually favor the skimmer slightly but that is a better situation in my opinion. The main drain circulation isn't all that critical anyway.