How long does the pump really need to run?

[mas985]

You say the headloss is about the same regardless of filter size, therefore they are very poor performers hydraulically speaking which doesn't surprise me as the pool industry designers are pretty lazy/useless/untrained?.

Actually it means just the opposite. Cartridge and DE filters have the lowest head loss so are are very good performers hydraulically. The head loss doesn't change with size because even the smallest size is "large". What causes the head loss in these types of filters is just the internal fittings and for DE, the backwash valve adds a lot of head loss but the media does not add much to the head loss. I can take the cartridges out of my filter and the pressure does not change which means they don't add any head loss. Only the internal plumbing fittings add head loss which is why it is so low. However, for sand filters, the sand area is quite small and that does have an impact on head loss but only for filters smaller than about 5 sq-ft.

Here is a table with several different types of filters and filter sizes (sand only). For a given filter line with cartridge and DE, the head loss does not change with size but as you can see, the cartridge has the lowest head loss and by quite a bit of margin.



Also, I didn't post the low speed pressure because it doesn't actually read a pressure. But theoretically, it is about 2 PSI.