How long does the pump really need to run?

[Anonymous [GDPR] European in the UK]

Yes Mark, I agree and I said if the filtration was good enough. I don't want to get into the area of colloids yet but the point was more that continuous running of the filtration but at a slower rate will improve the the water quality by removing more suspended solids because they are suspended and so can be skimmed and filtered and not just sinking to the bottom once the water has calmed. I have vaccuumed too many pools only to see small clouds created by dirt if you move too quickly or make sudden moves. Running the sysytem continuously has removed that problem. That said, I wonder if removing too much from the water would cause a greater loss of chlorine to photodegredation as the suspended matter may shield chlorine from the sun's UV in the same way as bacteria and algae can be shielded from chlorine as stated in your second link.

It is a fact that DE can remove Ocyst of Gardia and Crypto providing the grids are intact but DE is just a mechanical filter to go to the next level we need adsorption to draw particles to the surface of the filter media.

As you have a large cartridge filter and a good sized 2 speed pump, I would be interested in your flow rate and system pressure at normal running conditions if you wouldn't mind passing on that information please?
Regards
John

[mas985]

On high speed without solar, flow rate is around 68 GPM and with solar around 58 GPM. On low speed, flow rate is half of 68 GPM or about 34 GPM.

[Anonymous [GDPR] European in the UK]

Thanks Mark, What sort of pressure shows on the gauge at those flow rates? I usually fit sand filters but have a customer who specifically needs a cartridge filter and to get my system to run well the system pressure doesn't want to be too high.

Regards
John

[mas985]

High speed filter pressure is about 10 PSI without solar and 14 PSI with solar.

But I don't understand what you are trying to say here:

and to get my system to run well the system pressure doesn't want to be too high.

Cartridge and DE filters have about the same head loss independent of filter size. Only sand filters, because of the small area, have a head loss dependency on size.

Also when sizing a filter, you really should use the APSP-15 specs and don't worry too much about pressure. APSP-15 specifications use a rate of 0.375 GPM/sqft for cartridge filters.

[Anonymous [GDPR] European in the UK]

Happy new year Mark and thanks for the update. Yes with sand filters they only present a small surface area ( pi x r2 of the filter size) as the depth of the bed isn't considered for some reason so I would have expected the pressure to be lower with the large surface area of a pleated cartridge or DE grids. 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?

Helpful to know though thanks, On your slow speed I would have expected the headloss to drop quite a lot especially as your filter is quite big.

[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.

[Anonymous [GDPR] European in the UK]

Many thanks for that Mark, Chart saved for future reference.

What you have said about cartridge having the lowest head loss is what I was expecting. As you say the internal fittings are where the head loss occurs which is why I said the "designers" are lazy etc because it could easily be improved and needs to be given that we are going Eco. I have fitted a 15 PSI gauge to my filter as I needed to see the 2 PSI I run at also. I notice the almost exponential graph as the flow increases, which fits with my empirical data and is where I am investigating the head loss. Is it through the media or bad plumbing? Not an issue in the past as a powerful pump always makes sure the water gets where it's going but reducing the power brings on new challenges.

Thanks for you help on this, it's appreciated.

Regards
John