Intro: Converting a Sand Filter Into a Cartridge Filter
Last year my wife and I bought a house with a pool we were so excited. But all last summer we struggled with try to get the swimming pools water clear, it was always cloudy, and when I would vacuum debris would come back through the return jets.
After having a couple of pool professionals to look at are system the conclusion was that are sand type filter was to small for are system, and for them to upgrade it would be over a $1200. and to do it my self depending on the type of filter it would cost $600 - $800.
So after doing some research I figured that I could covert our system from sand to a cartridge filter system.
Total cost of this project was under $165.00.
Step 1: Filter Types
There are 3 types of filters Sand, Cartridge, and DE filters and each have there own routine for regulare maintanace
Sand filters are the least expensive and filter down to 20-40 microns
Cartridge filter are of medium exspence and filter down to around 8 microns
DE filters are the most expensive and can filter to 2-3 microns
Step 2: Cruching the Numbers
After deciding that I was going to go with a cartridge filter system, I now needed to see if the the tank to my sand filter was large enough and what size filters I can install in it.
The inside room that I had to work with 20" inside Dia and 17" in hight and 7" opening.
My pool is 32000 gal. the rule of thumb is a 100 squair feet to every 10000 gal.so I need a min of 320 square feet. I found Poolcenter.com and there sight has a section were you can plug in dimensions of filters. The filter that I found was the PLBS75 it has 75 square feet of filtering area and I would have to use a min of 5 to giving me 375 square feet of filtering area.
Step 3: Building the Hub and Outside Risers
After removing all the sand and laterals from the filter I figured that I could heat up and soften 1" PVC couplings and slip caps to fit over the exsiting hub instead of building a hub from scratch.
For the laterals I glued a 2" long piece of 1" PVC into a 1" slip and the other end into a female threaded street 90 degree elbow. I repeated this 4 times. For added security I installed stainless screws on the bottom side of the hub.
For each of the 4 outside risers I glued two 1" slip to male threaded ends to a 13 3/4" 1' pvc pipe. I drilled fourteen 3/4" holes in the pipe. For the top and bottom caps I used 4" furniture sliders that have a foam pad witch seals the ends to the filter. I drilled a 7/8" hole in the center and removed a 1 1/4" dia section of the foam . The bottom cap is secured with electrical nut. I needed it to be low profile because this end will thread into the 90 deg street elbow. The top is secured with a 1" threaded cap.
The last picture shows it installed inside the tank. To install it I had to disassemble it and reassemble it in the tank.
Step 4: Building the Center Riser and Installing the Filters
To get the length of the center riser I used 1 1/4" electrical pvc conduit (I had lying around) slipped it into the hub that was still in the tank and just marked it so the top of the riser is flush with the top of the opening. Then cut it to that length, again drilled fourteen 3/4" holes (I could have drilled more but didn't see any benefit, because the 14 hole have a greater flow rate than the risers dia.). I made a stop for the filter out of a 1/2" peace of 1 1/4" slip coupling (tapered at one end to seal the bottom of the filter) and a 1/4" peace of 1 1/2" pipe glued over the coupling peace to give it an extra shoulder. I slid it onto the riser a few inches up from the bottom, installed it into the hub again, slid a filter over the riser and then installed the valve body on top. Removed the valve, filter an the riser being carful not to move the stopper. Once out I marked its position I then glued it onto that spot.
Installing the filters was pretty strait forward. For the outside risers my first plan was to assemble them with the filters and just screw the into place. This was problematic due to such a small opening . I had to install the outer risers first and angle them so I could slide the filter over them, and install the top caps (hand tight). The center riser went flawlessly slip the riser into the hub, slide the filter over it, and installed an o-ring over the riser, then installed the valve and connect all the plumbing.
Step 5: Review of the System
Well it been well over a month and a half and it work GREAT. The pool is crystal clear. The starting pressure was at 10 psi. Its now at 15 psi so I pulled the filters and they were DIRTY. I expected them to be since the pool was de-winterized after I completed this mod, and it was in a desperate need of a cleaning.
In the future I plan on reworking the hub to accommodate 2 more filters that will bring the filtering area to 525 square feet