Pool Return Fittings and Jets

What does the eyeball's opening size change?

How fast the water leaves the wall. The same pump pushing through a 3/8 in. hole makes a fast, tight jet that throws a long way and turns the whole pool over; through a 1 in. hole it makes a soft, wide flow that barely moves the far end. So the small opening is the trick for a pool with a dead corner or poor surface circulation, and it costs a few dollars rather than a pump. The catch is that restricting the return raises the pressure the pump works against, so watch the filter gauge after you change it.

Will a fitting from another brand screw into mine?

Usually, because the thread is standard rather than proprietary. Most returns here are 1-1/2 in. male pipe thread, written MPT or MIP depending on the maker, and that is the same thread in the wall whoever built the pool. So an AquaStar eyeball generally goes into a Hayward body and a CMP cover onto a Waterway fitting. Check the size before you assume, since 1 in., 1-1/4 in. and 2 in. bodies all exist here, and a vinyl liner inlet is a different shape from a gunite one.

Which way should the eyeball point?

Down and away from the skimmer, not across the surface at it. Aiming a return at the skimmer feels right and works against you: it pushes surface debris past the mouth rather than into it. Point the jet slightly downward and angled so the whole pool turns in one direction, which carries floating debris round to the skimmer on its own and stops the bottom stratifying into cold layers. With more than one return, aim them all the same way round.

What is a venturi fitting for?

Moving more water than the pump sends it. A venturi fitting narrows the flow through its throat, which drops the pressure there and pulls extra pool water in through side ports, so the volume leaving the fitting is greater than the volume arriving. The point is circulation without more pump, which matters most on a variable speed pump running slow, where a plain eyeball leaves the water barely stirring. It is a fitting swap rather than a plumbing job.

Flush mount or a standard eyeball?

A flush fitting sits level with the wall so there is nothing to catch a toe, a hand or a vacuum hose, which is why they turn up on steps, benches and swim-outs. A standard directional eyeball stands proud and can be aimed, which is what you want where circulation is the job. Pick the flush one where people touch the wall and the directional one where the water has to be pushed somewhere. Covers and escutcheons here tidy either.