Filter size and pressures

[Hindsight]

First off, thank you to all the members of this community. I have never had a pool and the depth, breadth, and wealth of knowledge shared by people on here is truly amazing. This newbie is truly appreciative, especially the BBB method. Now trips to walmart instead of the pool store

I have a Pentair sd80 filter (3.15 sqft, 70 gpm) that is 3 years old and just found that it sprang a leak near the seam at top. It is clearly a hole in the housing and now way associated with a seal or fitting. After reviewing several threads, this seems to be a fairly common problem associated with Pentair.

Anyways, one of the things that I have noticed, after reading through many of the threads is that, most people have a pressure readings are in the 15-25 psi range. When our system was installed, it was reading 30 psi at start up. We would wait and backwash when the psi got to 38-40 range and it would drop back to 30-31. I thought that this was just it's "normal operating" range. I also, this spring, did a deep cleaning on the sand filter and again the psi stayed in 30-40 range. I have all my skimmer lines and return lines fully opened.

My question would be.... If I went to a larger filter, say a filter in the 4.7-4.9 sqft and 100gpm range, would that drop the pressure down at the filter. Since my filter sprang a leak, I am hesistant to return with the same filter and have the same higher operating pressures.

 

[kimkats]

HI! Welcome to TFP!

Every pool and set up is different. While that does seem to be a higher pressure reading than what you have found it seems to be what your system is good with. I really don't think the pressure had anything to do with the hole.

A bigger filter will require less cleaning so that is a good thing.

Do you have equal flow our of your returns?

Kim

 

[gregpsaros]

Ha just posted a thread with the same questions and the same filter, but I'm only wondering what normal pressure should be. Mine runs about 13 to 15 psi when clean, and I assumed that this was normal. Having a lot of trouble keeping the water clear this year, and read the label and saw the maximum operating pressure is 50 I think it said for the sd80. I'm wondering if I'm not using it to its full capability and that's why my water is cloudy. If you find out anything please let me know!

 

[Hindsight]

Thank you for the reply KimKat. Yes all the flow/pressure was equal on the returns (4 of them). I do think that a bigger filter is probably what I will go with, just for the fact that less cleaning is required. As far as performance is considered, the Pentair sd80 did a very good job of keeping the water clear and was fairly easy maintenance. However for it to blow a leak in just 3 years is rather disappointing.

Gregpsaros- You follow my thread and I will follow yours, maybe we can piece this thing together lol

 

[kcindc]

Ha just posted a thread with the same questions and the same filter, but I'm only wondering what normal pressure should be. Mine runs about 13 to 15 psi when clean, and I assumed that this was normal. Having a lot of trouble keeping the water clear this year, and read the label and saw the maximum operating pressure is 50 I think it said for the sd80. I'm wondering if I'm not using it to its full capability and that's why my water is cloudy. If you find out anything please let me know!

Cloudy water is all about bad chemistry. Do you have one of the recommended kits? Can you post up a full set of results from one of the recommended kits?

 

[gregpsaros]

That's what I've been figuring, but just starting to wonder if the filter is a big part of it. Been keeping it at shock level for 5 days now. Able to see the drain for the first time this season yesterday. I have a k2006.

FC has been 11-18, trying to keep 16
Ph 7.2
CC <or equal to .5
TA 115
CH 140
CYA 40

 

[domct203]

That's what I've been figuring, but just starting to wonder if the filter is a big part of it. Been keeping it at shock level for 5 days now. Able to see the drain for the first time this season yesterday. I have a k2006.

FC has been 11-18, trying to keep 16
Ph 7.2
CC <or equal to .5
TA 115
CH 140
CYA 40

As your filter psi rises, your flow rate decreases. As your flow rate decreases, the volume of water you are filtering is also decreasing, which means it takes longer to clear the pool. This is why we always recommend backwashing when the filter pressure raises 25%. Depending on system head losses, that could be a flow reduction in the 40-50% range.

 

[gregpsaros]

As your filter psi rises, your flow rate decreases. As your flow rate decreases, the volume of water you are filtering is also decreasing, which means it takes longer to clear the pool. This is why we always recommend backwashing when the filter pressure raises 25%. Depending on system head losses, that could be a flow reduction in the 40-50% range.

I agree just wondering, for example, say there's no sand in the filter and in service it runs at 10psi. Add a little sand and it's 15. Add the correct amount and it's 25 clean and even though it's higher pressure, the more sand filters more and outweighs the downfall of lower flow. I bought the house from flippers and not sure if they put the right amount in and wondering if there's a way to determine what pressure should be normally

 

[domct203]

There is no 'normal' pressure, everybody's pool is different. When I run my suction side cleaner I will remove the return jet eyeball to keep the water still while the vac is running. When I remove the eyeball my filter pressure drops 4 psi. I am currently using a 1" eyeball because it not only reduced the velocity of the water, but it dropped filter psi about 0.5-1 psi compared to the 3/4" eyeball.

When my solar comes on, my filter pressure rises 3 psi.

As you can see, system backpressure (which is what you see on the pressure gauge) can vary quite a bit from pool to pool.

Now, back to the OP's questions......

As mentioned, the bigger the filter, the better. Not only will it require less backwashes, it will flow more water which should be a good thing for your 2HP pump.

 

[Hindsight]

My current plumbing from the pump to multivalve intake is 1.5" and the same for the multivalve outlet which goes to heater. Looking for a larger filter, I have noticed that the sizes of the intake/outlet are 2". Would there be issues with pressures in the pump or at outlet using an 1.5"-2" expansion at the intake and 2"-1.5" reducer at the outlet?

 

[gregpsaros]

There is no 'normal' pressure, everybody's pool is different. When I run my suction side cleaner I will remove the return jet eyeball to keep the water still while the vac is running. When I remove the eyeball my filter pressure drops 4 psi. I am currently using a 1" eyeball because it not only reduced the velocity of the water, but it dropped filter psi about 0.5-1 psi compared to the 3/4" eyeball.

When my solar comes on, my filter pressure rises 3 psi.

As you can see, system backpressure (which is what you see on the pressure gauge) can vary quite a bit from pool to pool.

Now, back to the OP's questions......

As mentioned, the bigger the filter, the better. Not only will it require less backwashes, it will flow more water which should be a good thing for your 2HP pump.

I see, thanks for the info. I guess I'll leave it for now then. Sorry I'm done, not trying to hijack the thread