Quote Originally Posted by DennisP
Again, I fail to see any downside to a main drain... Clogs??? Really??? that does not make sense... I also fail to see why you would have any more leaks there than with any other fitting anywhere else...
You don't necessarily have more incidents with a MD than a skimmer but it is far easier to fix a skimmer leak or clog than it is a MD. I have seen many POs that think it is a good idea to use their MD for spring clean up and create a massive clog.



So, yeah, go ahead and bemoan the whole main drain issue all you guys like, but it is fact that cooler water gets pulled into the main drain thus causing quicker heating and overall better mixing within a shorter timeframe. To say otherwise is being obtuse. Sure you can argue that you can aim returns, use lower on-wall suction points, etc, etc... fact of the matter is water in on the sides aimed to swirl the pool and water going out the skimmer as well as the main drains will maximize the mixture way better than using a skimmer alone. To argue anything else is just being foolish and goes to show a bias against main drains for a whole host of reasons other than what I have stated.
So I guess I am going to have to be foolish again as I have solar and have measured temperature differences from the surface to the deepest end (9') and saw no difference in temperatures with or without the main drain (I have one return that is pointed into the deep end). It really doesn't take much to mix up the water and almost any return is sufficient unless the pool is really deep.


Quote Originally Posted by Teapot
Why can't we run pools like HVAC system? I do, I have for 4 years.
What I really meant by that is that an HVAC fan will do fine with equal friction loss on both side but a pool pump will not. But I bet if I did a head loss calc on your setup, the head loss is not exactly the same on both sides of the pump and therefore the two sides are not exactly equal. If they were, you would probably have cavitation at higher RPM. Low RPM doesn't matter because the pump cannot cavitate on lower speeds.

Also, a PO on another forum thought he was being smart and energy efficient by running a separate line for every return (i.e. keep the pipe size AND ports the same on both sides of the pump). Combining that with a low head loss cartridge filter and the pump was cavitating severely. The only options for him was to either throttle the return with a valve or down size the eyeballs. At least with the latter, the higher exit velocity does some useful work while throttling just adds head loss.


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.
A bullet has far higher density than water and so it will sink before reaching the other side. Higher exit velocity of water will simply move in a straight line and the faster it moves, the faster it will get to the other side. One way to make a spa jet feel stronger is to use a smaller orifice spa jet which increase the force per unit area. When I changed my return eyeballs from 1" to 3/4" and I saw a noticeable difference in debris movement to the skimmer on low speed. However, there was only about a 1/2 PSI rise on pressure but I do have 4 returns. The smaller returns make the flow more directional but it also helps to move the surface water better at lower RPM for better skimming action. If the larger eyeballs are working for you then fine, use them. I was only saying that the smaller eyeballs can have benefits for certain situations.