Quote Originally Posted by mas985 View Post
I have a little bit of a problem with this statement. You actually don't want the returns to have the same area as the suction ports. Pool plumbing is not the same as HVAC. If the return head loss gets too low when compared to the suction side head loss, the pump has a tendency to leak air into the pump basket and even cavitate. In general, you want the return head loss to be several times that of the suction head loss and restricting the returns with eyeballs is a good way to ensure that while still providing useful work.
mas985, I totally agree with you, it's a lot of your information that I have used in the past, you filter comparison chart saved me hours of work but and this is the big one! Why can't we run pools like HVAC system? I do, I have for 4 years. It's a paradigm shift away from the old idea of big power guzzling pump which when you take the head away will cavitate, complete agreement on that. Now I gravity flood my pump with below the water level placement so suction side headloss is low. the system pressure on the tank gauge is around .25 PSI when I am running slow (no swimmers and over night) and 0.75 PSI at swimming daytime running normal. I might get 2.5 psi when backwashing. The biggest difference is the power my setup consumes, slow running I move 1320 US gallons per hour at 30 watts of electricity. Daytime running 1981 US gallons per hour at 69 watts. this give me 4 turnovers per day or there abouts. The pump runs 24/7 to ensure any debris falling into the pool still gets skimmed out rather than sinking and the slower flow has meant water quality has increased, Previously without flocculation the water was around 5 NTU's still really clear to the eye but slower filtration brought this down to 1 NTU.

On a bigger pool, my customers we have a bigger setup, that runs at 50 watts over night pushing 2588 US gallons per hour and 125 watts during normal times and pushing 3777 US gallons per hour. Technically he should run more to get 4 turnovers in 24 hours but he prefers to save the money and the pool water is still exceptional.

In reality the old pool way is power hungry, wasteful and inefficient on filtration (the whole point of what we are doing)
We really just want to move water from the pool, through a filter and back to the pool and that is simply what I do. The idea of producing excess friction to the point of loading the filter to 15 PSI normally is just some old dinosaur idea that has become the track pool builders run on but it's not required. The the big pumps we use are redundant and as you quite rightly say will cause cavitation if used on a highly efficient setup. Don't build the plumbing to suit the pump issue build the pump to suit the plumbing around the same as HVAC It will save $1000's.

Quote Originally Posted by mas985 View Post
Plus return eyeballs serve another useful purpose. With higher exit velocity the water reaches more distant parts of the pool faster so mixing and circulation are a little better with smaller eyeballs. It does reduce flow rate but not by much and studies have shown (see sig) that flow rate and turnover are not all that important to pool sanitation and circulation.
Do they? I have an issue with that statement and here is why. There are a few guys on Youtube (The slow Mo Guys) they fire an AK47 assault rifle under water in a pool. The muzzle velocity of an AK47 is 715 m/s (2,350 ft/s) yet in water the bullet travel 5ft. Instead I prefer to balance the size of the outlets to the plumbing and use the larger flow of water to move more water rather than a smaller faster (temporary) flow, It's like a locomotive at slow speed coming into the station, is bigger and moving slower but will destroy the station if it hits the buffer without the brakes.
https://www.youtube.com/watch?v=cp5gdUHFGIQ

I do agree with turnover rates etc, what is the point? you can turnover the water as many times as you want to pass some regulation etc but if the filtration isn't fine enough you are really just re circulating the small stuff. Chlorine has already killed the bacteria and those that are resistant and oocytes are too small to get caught in most filters so you may as well not bother and just fit a strainer at 30 microns. My filtration removes stuff to 4 microns so I am having an effect, I can use flocculation to remove even more. The need to run slower but keep moving is to ensure floating debris goes into the skimmer not to the bottom, that is why I sold my pool robot 3 years ago.