Pressure

[Spensar]

It remind me of the 80s doo hickeys that you only had to install in your fuel line to save big on gasoline.

[Charlie_R]

If I close the skimmers and have just the main drain I get all that air. The water coming out of my returns were never as hard as it has been this year. Again, when the pressure starts to register in the 30's from the 20's it seems to clear up. It just seems like the water pressure coming out of the returns is way too strong.......the circulators should not be a concern, just mentioned I put them on and when you do the pressure on the filter goes up because as you say it causes a lot of back pressure. If I dont have them on and run the pump for so long and the pressure goes up because of being dirty, the same thing happens, the air dissapears.

Better start checking all the tubing between your main drain and filter. In certain conditions, a small crack or unglued joint will not leak water, but if put under a slight vacuum, will allow air in. Also, check to see that your main drain doesn't have any debris (hair, leaves etc) under the grate, reducing the amount of water flow available.

I have seen cavitation happen at sharp 90 bends under vacuum conditions in hydraulic systems and this might be a possibility here as well.