Minimum flow rate discussion

[andyjman1983]

Mod Edit: Split from this topic:http://www.troublefreepool.com/pool-filter-for-18x33-t66036.html moderator linen

Look up the gpm ratings of both of the pumps, and the look at the minimum flow rates on the filters your looking at. If you have a filter that's at least 60 gpm minimum u want a pump that flows at least that. 2 inch plumbing would be good for your setup. No matter what you do you will want at least 2 suctions and 2 returns for a pool that big. I actually have 3 of each for my 18x48x4. If you don't, your pump and filter combo will starve for water.

Btw I just got the intex 2650gph sand filter and I love it.

 

[linen]

Re: Pool filter for 18x33

Look up the gpm ratings of both of the pumps, and the look at the minimum flow rates on the filters your looking at. If you have a filter that's at least 60 gpm minimum u want a pump that flows at least that. 2 inch plumbing would be good for your setup. No matter what you do you will want at least 2 suctions and 2 returns for a pool that big. I actually have 3 of each for my 18x48x4. If you don't, your pump and filter combo will starve for water.

This is incorrect. For cartridge filters (and in general most filters) you want a low flow rate. The exception is backwashing requirements (mainly impacts sand filters). Since the op is looking at a cartridge they can go a big as they want. See: http://www.troublefreepool.com/hydraulics-101-have-you-lost-your-head-t915.html

 

[andyjman1983]

Re: Pool filter for 18x33

When I posted, the numbers I posted were ragarding minimum flow ratings. Yu want a pump that flows at least the minimum stated on the filter or else it won't work properly. As was also stated, a larger system is better when you are discussing cartridge systems.

 

[linen]

Re: Pool filter for 18x33

When I posted, the numbers I posted were ragarding minimum flow ratings. Yu want a pump that flows at least the minimum stated on the filter or else it won't work properly.

Again, this is not true. Except for backwashing requirements, there are not minimum flow rates that I am aware of for filters. Filters work better with lower flow. The design flowrates that are speced are where the filters ability to filter starts being reduced.

 

[andyjman1983]

Re: Pool filter for 18x33

Every filter I have ever seen states a minimum flow rate. What will happen especially with a cartridge filter if the flow rate is below the minimum most of the dirt and other contaminants will go through the lower parts of the filter only clogging it prematurely. They also state a minimum flow rate due to the internal pressure drop of the filter. If your pumps too small it'll have trouble pushing the cleaned water thorough the filters cleaning media. The only ones that will not usually state it are bundled systems where the pump and filter come on one skid or as a kit because the manufacturer has already sized the pump and the filter together. The reason manufacuteres spec a minimum flow is because they don't want someone using a pump that will start to deadhead once the filter starts to load up and loose efficiency.

Not trying to argue or cause issues but I want the op to get a setup that will work fine for him.

 

[andyjman1983]

Re: Pool filter for 18x33

Here's a helpful link. It covers pumps, filters, and pipe size.

http://www.poolplaza.com/pool-pump-sizing-2.shtml

 

[andyjman1983]

Re: Pool filter for 18x33

Linen is correct though. Filters, especially cartridge filters work better with lower flow. There's much less chance of pushthrough and the lower flow rates make sure that you don't damage the filter. As was also stated, the larger the filter the less you'll have to clean it too.

 

[linen]

Re: Pool filter for 18x33

The manufactures do not spec minimum filter mode flow rates (at least pentair and hayward), since filter efficiency goes up with reduced flow rate. Can you point to a spec that shows one?

The link you posted was talking about pool turnover in reference to minimum flow rates and not minimum flow rates specific for filters. Also, in that link when discussing filter specific flow rates it only shows maximum.

 

[andyjman1983]

Re: Pool filter for 18x33

I have seen it posted before, but it mostly tends to pertain to sand and de filters in order to have an efficient backwash process. I have even seen it on those cartridge filters that take de. I forget what the classification is called for those types of filters. It is also mentioned in this link...

http://m.wikihow.com/Select-the-Correct ... mming-Pool

But they might be misinformed when it pertains to cartridges.
My mistake.

 

[linen]

Yes, as mentioned above, minimum flow rates are only speced for backwashing:

The exception is backwashing requirements

There is no minimum specification for minimum flow rate in filter mode when discussing just the filter.

Some confusion does come from discussing how many "turnovers/day" the pool needs. When sizing a pump (not a filter), often a certain number of "turnovers per day" is used to get a rough of idea of pump size. For example, 1 "turnover" in 8 hours. In reality, most pools can get by with much less "turnover" than this and still have acceptable clarity in the water (this is pool owner subjective). In my pools case, I can run on low speed for 4 hours and have great water clarity...but I only move about 4800 of my 11000 gallon through the filter...which is fine. This is covered in this pool school article: http://www.troublefreepool.com/pool-school/pump_run_time

 

[mas985]

Linen is correct. Filters are speced for MAXIMUM flow rates and not minimum flow rates. ALL filters work better at lower flow rates. Otherwise, VS/two speed pumps could not be used. Also, the Poolplaza link confirms this as well. Look at the table "Check the FILTER FLOW RATE" in Step 2. They show the maximum flow rate and the "Best Flow Rate". Best flow rate is simply 75% of the maximum and actually means "Not to Exceed". Anything less than that flow rate is fine.