Is there a minimum flow rate for cartridge filters? I want to do very low GPM

[shaneTX]

Hi,

Does a cartridge filter lose effectiveness at very low flow rates?

I'm looking to size out new equipment for my pool. I have a hayward ecostar variable speed pump. I was envisioning running my pump hard for a few hours and then running it at low speed for the rest of the day to keep flow rate going and to save power.

When I look at the specs for a Hayward starclear120, I see a "performance range" of 75-120GPM and a design flow of 120 GPM.
If I run my pump at low speeds, I get ~45 GPM. Will the filter not work as well at low speeds? What happens below the performance range specs of a filter?

 

[jblizzle]

Welcome to TFP!!!

Nope. In fact it should filter better at lower flow rates.

We recommend sizing the filter based on your pool size and season. Generally go as big as you can afford. The filter specs are maximum recommended flow rates, there is no minimum.

 

[Jimrahbe]

Shane,

Welcome to TFP... A Great resource for all pool owners with "flow issues"....

I run my pump at 1,200 RPM and at that speed my filter pressure is only 2 or 3 lbs... Because of this I only have to clean my filter twice a year. Actually, I could really only do it once a year but my OCD keeps getting in the way...

I agree with Jason... as far as filters go, the bigger the better...

There is really no need to "run your pump hard"... The only reason I increase my speed is to run my water fall once a day for 15 minutes. I used to increase my speed to "help skim the surface", but found it did not make any real difference. The surface stays clean even at 1,200 RPM.

Thanks,

Jim R.

 

[Donldson]

Agree with above. I switched to a sand filter this year for simplicity (and most water clarity comes from proper chemistry) and oversized it for my pool. I run it on low speed for about 8 hours per day and the water might even be a bit clearer than with the cartridge. I clean my filter about once a month, much like Jim more because I want to than necessarily need to, and everything runs well. The power bill certainly appreciates it!

 

[shaneTX]

Shane,

Welcome to TFP... A Great resource for all pool owners with "flow issues"....

I run my pump at 1,200 RPM and at that speed my filter pressure is only 2 or 3 lbs... Because of this I only have to clean my filter twice a year. Actually, I could really only do it once a year but my OCD keeps getting in the way...

I agree with Jason... as far as filters go, the bigger the better...

There is really no need to "run your pump hard"... The only reason I increase my speed is to run my water fall once a day for 15 minutes. I used to increase my speed to "help skim the surface", but found it did not make any real difference. The surface stays clean even at 1,200 RPM.

Thanks,

Jim R.

Thanks Jim..

So when your filter is only running at 2-3 PSI, at what range do you know it's time to clean it? When I run at high speeds, I generally backwash when the filter increases 10-15PSI.


-shane

 

[jblizzle]

We recommend that you clean the filter when the pressure rises 20 - 25% over the clean pressure. That pressure check should be done at a higher speed so that you can actually differentiate the pressures.

 

[setsailsoon]

I completely agree with Jason and others here. 25% above clean at normal flow rates is the time to clean. Cartridge filters actually filter small particles more effectively when they are a little fouled. I clean mine every couple of months and it's still only 1/2 fouled. As the lower part fouls water flow naturally diverts higher on the cartridge. You can look at this when you clean to see if you're cleaning too soon. As one person mentioned the higher pressure drop cost's a little in electricity so if power is very costly this could be an issue but in most cases the increased cost is negligible until you exceed the 25%.

Chris

 

[Jimrahbe]

Thanks Jim..

So when your filter is only running at 2-3 PSI, at what range do you know it's time to clean it? When I run at high speeds, I generally backwash when the filter increases 10-15PSI.


-shane

Shane,

After a while you get to know your pool... I know my filter never gets dirty enough to notice when running at 2 or 3 psi... I just don't worry about it and automatically clean them at the end of the swimming season while it is still hot enough to get wet, and then again before the season starts and hot enough to get wet.

Jim R.

 

[tonygiotta]

After a while you get to know your pool... I know my filter never gets dirty enough to notice when running at 2 or 3 psi... I just don't worry about it and automatically clean them at the end of the swimming season while it is still hot enough to get wet, and then again before the season starts and hot enough to get wet.

Jim R.

Just so I can wrap my head around this... Did you mean to say your pressure reading never gets high enough to notice when running at 2 or 3 psi? Because it is still getting just as dirty for any given period of time, regardless of whether you run your pump at high speed or low speed, right?

 

[Jimrahbe]

Just so I can wrap my head around this... Did you mean to say your pressure reading never gets high enough to notice when running at 2 or 3 psi? Because it is still getting just as dirty for any given period of time, regardless of whether you run your pump at high speed or low speed, right?

Tony,

What I was trying to say is that if I clean my filter and then measure my pressure at 1,200 RPM it is about 2 or 3 psi... After 6 months, at the same speed, it is still 2 or 3 psi...

If I increase speed, the pressure will go up... at 1,500 RPM it is 4 psi and at 2,000 RPM it is 7.5 psi...

I was also trying to say that since I have a VS pump and a large filter, I don't worry about the 25% rule, one way or the other...

Thanks,

Jim R.

 

[tonygiotta]

Got it, no noticeable pressure increase caused by a dirty filter when running the pump at slower speeds. Makes sense...