Help with "shrinking" a filter. Please help

[nabril15]

Hello
I have a Starite Posiflo II PTM135 filter that spans 41" tall. Whenever I clean it, I only see dirt, leaves, whatevers, on the bottom 1/3 of the filter; the top appears to be clean.

I want to build a protective shed around it, and 41" is too tall. In looking at my filter today, I thought about possibly eliminating the center section, and this reducing my height by 14". I can loosen the tightening rings, remov ethe center section, and attach the top section to the bottom one. Naturally, I need to buy a smaller cartridge, which I am still looking for; I assume that it exists - same diameter as my current one, but shorter. I found this one, Sta-Rite PXC-175, at 28 3/16" tall wiht the same diameter, that may work. If you look at the attached pic, you will see what I have (on the left), and what I want to achieve (the one on the right).

Am I crazy for trying to do this? Can some of you kindly convince me in favor or against? In theory, I shouldn't lose any suction or return power, right? I have a 16k galloon pool, with a 1.5 hp pump, and I use my navigator pro cleaner as my main source of intake; if the water level allows, I switch to skimmer.

Thank you

 

[JohnT]

Though the heavier stuff is going to tend to be captured near the bottom of the filter, the things that are more thoroughly mixed in the water like dust are going to be trapped everywhere. A smaller cartridge will have more resistance to flow which will reduce your suction and the return flow.

 

[samiguy]

Question....what are your pressure readings on clean and then "dirty" filter? Are you able to bleed off the air when starting the pump?

 

[nabril15]

Question....what are your pressure readings on clean and then "dirty" filter? Are you able to bleed off the air when starting the pump?

thank you both for responding.
At present, my pressure reading is around 5psi for the vacuum line (Navigator). If I switch to main drain or skimmer, it goes up 10 psi or so. I cleaned it recently so I dont recall what my "new" dirty reading will be.

I've never had such a low reading as 5psi on the vacuum line, so something must be happening; I do see quite a few bubbles coming out of my return when I run the vacuum line, and I haven't been able to figure out why.

 

[gtemkin]

I'm guess I'm not seeing the center section you want to remove in the pictures. In the left side photo, I see a bottom section and a tall top section (your current filter) and in the right side photo I see a bottom section and a short top section (the one you want to achieve) but I don't see any center section. Are you thinking of cutting a center section out?. Please clarify, thanks.

 

[nabril15]

My apologies. Here is an actual picture of my filter.

 

[duraleigh]

One of the biggest issues with a lot of pools on the forum is filters that are too small. I would not reduce the capacity.

If it ABSOLUTELY has to be shorter, get a sand filter of equal capacity.

 

[nabril15]

Though the heavier stuff is going to tend to be captured near the bottom of the filter, the things that are more thoroughly mixed in the water like dust are going to be trapped everywhere. A smaller cartridge will have more resistance to flow which will reduce your suction and the return flow.

thanks John.
Would you mind kindly explaining your statement below further? Not to repeat it, but I am just typing it out loud to see if it makes English sense. A smaller cartridge create a backup of water (if you will), and this reduce the return flow; this will reduce the suction. Did I say it correctly?

Wouldn't a smaller filter mean less friction with the cartridge material itself (the paper/nylon/whatever coils), and thus more water would flow through?

 

[samiguy]

My thought is that with a smaller element, you would get higher pressure and then create more "blow threw". Lower pressure and higher volumn is my understanding of getting the most bang for the buck. Smaller filter would restrict flown and hense not flow as much water. Just my basic understanding. The more flow I get, the cleaner and faster my filter works. Mine runs at about 5psi with new/clean filter and I then us some synthetic DE to help get the real fine matter. Good Luck and let us know how it works out.
Sami

 

[gtemkin]

Wouldn't a smaller filter mean less friction with the cartridge material itself (the paper/nylon/whatever coils), and thus more water would flow through?

Whenever I'm trying to figure out the relationship between 2 different factors, I like to take it to the most extreme case to see what would happen.

Therfor, imagine you downsized your filter to the size of a thimble. First of all, the small size of the thimble would be like a blockage when compared with typical pool pipe sizes so there would be reduced water flow. In addition, that thimble filter would fill up with dirt and bugs, etc pretty darn quickly, further reducing flow.

That's what happens when you reduce the size of a filter.

 

[Bama Rambler]

Forcing the same amount of water (or anything) through a smaller area (filter media) means that it has more resistance to flow which means that it requires higher head pressure to push it through the media. Think of the filter media as an orifice. THe larger the media the larger the orifice and thusly the more water will flow through it. If you reduce the media then you reduce the amount of water that can flow through it.

 

[nabril15]

During a water check at Pinch a Penny, I asked my shrinking filter question to one of the staff which seemed knowledgable. He informed me that I cant just remove the middle section because the Starite Posiflo filters are designed with an internal diameter that gets smaller as you move towards the bottom (sort of a V shape, though not quite that drastic). So that my top section will not fit nicely over the bottom section. He did suggest that if I find the top for a PTM100 which will fit over my bottom section. So, in trying to find one on ebay or wherever I came across some literature for this filter in the attached pdf.
It shows tha tmy PTM135 can handle up to 65,000 gallons in 8 hours, which is WAAAAYY over my pool's capacity of 16k gallons. The PTM 100 can handle up to 48,000, and the PTM70 can handle up to 34,000 gallons; I hope I am interpreting that correctly.

Does my logic and interpretation make sense? If a smaller filter (the 70 or 135) can handle the gallons, I should be ok to downsize. No?
Thanks

 

[Bama Rambler]

Looks as though you're determined to do this even if you've already been told that it's not suggested. Try it and let us know how it works out for you.

Our recommendations for filter size is based on real world experience. You're better off looking at the recommendation for commercial pools if you're going to look at the filter size.

 

[nabril15]

Dave...I don't mean to ignore or undervalue the advice here. I take forum advice to heart.
Since buying this house I've discovered so many things that were done wrong by the previous owner, that I second guess most things that I come across in the house. I will not do this if it will screw up my pressure. But, if the starite document states that the ptm135 filter can handle 64k gallons in 8 hours, perhaps the previous owner went overboard in buying the ptm135; or the salesman took him for a ride, and he didnt seek help in these valuable forums. And it might be worth looking into the ptm100. Am I wrong?
Perhaps a smaller filter may mean that I need to run the pump a bit longer to circulate all the water. Fine, I will consider that.

I am simply exploring all of my options with good information. I appreciate the help in these forums tremendously.

 

[cmdrdata]

It seemed to me that your filter is larger than needed for your pool size, however, in this case I am of the opinion that bigger is better for these reasons:

1. Time between cleaning your filter elements will be much longer - meaning less work for you
2. Your pump motor don't have to work as hard since there is plenty of surface area for on the filter thus pressure rise due to clogging of the filter will be much less - meaning lower power consumption
3. Filter efficiency will probably be effective longer, thus you don't have to run your pump as as long as the smaller filter - again energy saving and less wear and tear on your equipment.

I'd personally leave it alone.