Flow rate question: cartridge filter with 1.5" inlet/outlet connected to 2" pool plumbing system

[Cameljockey]

Will replacing my current 2" sand filter with a 1.5" cartridge filter reduce water flow at the pool jets ? The pool pipework is all 2" but there will be a 2" to 1.5" reducer into the filter, and one will be fitted at the filter outlet the other way around 1.5" to 2".

The filtration capacity is large enough for the size of my pool, but will the two 1.5" connections in and out of the filter cut down water flow to my pool as all pipework is 2". The next sized filter has 2" inlet/outlet but is obviously more expensive and its increased filter capacity is not required. I do already have the smaller filter and getting the seller to replace it might be difficult anyway.

I also wonder as the cartridge filter is replacing a sand filter, will this give a reduction in flow resistance and maybe increase throughput to compensate?

I'm aware there are many other factors which affect flow through the system, but this is my only concern, because with the current sand filter the output at the jets is fine. Am I worrying over nothing?

Thanks for any help you can give.

[Denniswiseman]

The fact you say "The filtration capacity is large enough for the size of my pool" means that the flow would be correct through 1.5"
My Pool is 45k with 50mm pipework but the MPV has 1.5" connections with no problems
You could work out the total returns area against the 1.5" (D x D X 0.7854) to see if there is any restriction on flow
D = the diameter

[Cameljockey]

The fact you say "The filtration capacity is large enough for the size of my pool" means that the flow would be correct through 1.5"
My Pool is 45k with 50mm pipework but the MPV has 1.5" connections with no problems
You could work out the total returns area against the 1.5" (D x D X 0.7854) to see if there is any restriction on flow
D = the diameter

Thanks Dennis. I'm afraid I didn't explain correctly, my fault. I don't worry about water filtration, I understand your point. My worry is that my pool has one 10 metre horizon edge, into an overflow tank the length of the pool, and if the water flow from the jets drops there won't be enough flow to keep the water falling across the whole 10m length of the egde. It already doesn't flow over the edge of the last metre due to that part being built just a centimeter or two too high, so I'd say the current flow is just adequate.

I hope that explains better.

[Denniswiseman]

That is something different then
You normally match a pump to a filter so that you are not forcing to much through the filter and reducing filtration
I would suggest you have a flow meter fitted to see what flow you need to maintain your existing flow and then checkout the maximum flow through your new filter
An option to get a decent flow for the infinity edge is not to pass all the water through the filter and just return it to the pool unfiltered or possibily fit an additional pump and bypass the filter
An infinity edge aerates the water and raises the pH which would have to be reduced with muriatic acid quiet often. It may be an idea to not run the infinity edge all the time to stop this

[Cameljockey]

That is something different then
You normally match a pump to a filter so that you are not forcing to much through the filter and reducing filtration
I would suggest you have a flow meter fitted to see what flow you need to maintain your existing flow and then checkout the maximum flow through your new filter
An option to get a decent flow for the infinity edge is not to pass all the water through the filter and just return it to the pool unfiltered or possibily fit an additional pump and bypass the filter
An infinity edge aerates the water and raises the pH which would have to be reduced with muriatic acid quiet often. It may be an idea to not run the infinity edge all the time to stop this

These are great suggestions I didn't consider. I believe my I'm about to fit the new filter so I can incorporate a new pumping arrangement, I have plenty of space in the pump room.
I think my 180 kPA pump and 17 cbm/hr filter are matched, I hope so.

The PH stays in range because the infinity edge is just a gentle trickle, I like it that way so it's not a problem. Its main function for me is to keep the pool surface leaf/insect free.

Thanks once again Dennis, you are always such a helpful guy.

[Denniswiseman]

Glad to be of help. At least you have some options available now

[Teapot]

Thanks Dennis. I'm afraid I didn't explain correctly, my fault. I don't worry about water filtration,
Well you should. That is whole point of filtration how much dirt and nasties can you remove from the water and not whether the last meter of the infinity edge looks pretty!

I understand your point. My worry is that my pool has one 10 metre horizon edge, into an overflow tank the length of the pool, and if the water flow from the jets drops there won't be enough flow to keep the water falling across the whole 10m length of the egde. It already doesn't flow over the edge of the last metre due to that part being built just a centimeter or two too high, so I'd say the current flow is just adequate.

I hope that explains better.

Now back to your filter, That is a massive pump for that little pool and filter, are you in the USA? Single or 3 phase? You could save a lot of money with a speed controller if you don't want to change the pump. You have not given us the cartridge filter model so only have your word that it suitably sized. Your sand filter almost right size for the pool but not the pump and flow rate, has a multiport valve which really interferes with the flow. Your cartridge filter doesn't have multiport so a much lower headloss will mean a much higher flow (what micron are the filters?) even with the smaller fitting which won't make much difference.

Slower filtration is better filtration, with the force of your pump dirt etc will be pushed and squeezed through the cartridges resulting in some break through so reducing the overall filtration and costing you lots more to achieve less. If for some reason (high batherload etc) you want a high flow/turnover rate you need to increase the size of the filter to accommodate it rather than trying to push too much water through the smaller one. If it's a domestic low batherload pool then take a step back and think do I need such a high flow? How many hours does your pump run for?