My feedback on main drains in an above ground pool...

[mas985]

Many PBs are building pools now without main drains but not because they don't have a clue or because they are trying to save costs but because studies have shown that they really don't contribute much to the sanitation and cleanliness of a pool. Here is one such study done by the APSP: http://apsp.org/portals/0/PDFs/Case%...n%20Drains.pdf

The video at the end shows how ineffective a main drain really is even at very high flow rates. I have confirmed this myself with my own pool since I have a MD and have operated with it on and with it off and I saw absolutely no difference in water quality or bottom cleanliness. I once dumped a bucket of small debris around the MD and even with the pump running over 8 hours with ONLY the MD running, only the first couple of inches around the MD were free of debris. Because of the VGBA, MDs are now designed to have very low water velocity to reduce the risk of entrapment which makes these MDs even worse at drawing in debris. While you may have seen debris setting around the MDs, that could be due to the slope in the floor rather than the MD itself.

But there is another significant reason not use MDs. Skimmers require a certain flow rate in order to effectively draw in debris. Some manufactures recommend at least 15 GPM. With the addition of an MD, it steals water from the skimmer and there may not be enough suction on low speed of a two speed pump so running on high speed may be necessary which is about 4x the energy use. Same is true with a VS pump. More suction ports require higher RPM settings and higher energy costs.

Sorry but I really think you are fooling yourself into thinking that the MD is actually doing anything at all. The evidence simply doesn't support it.