Pentair R173409 Filter Cartridge
Pentair OEM number • 50 sq ft • 7″ OD × 19.625″ long
R173409 is Pentair's number for this cartridge, not a part you have to buy from Pentair. The filter itself is a 50 square foot cartridge measuring 7 inches across and 19.625 inches long, and Pleatco, Unicel, and Filbur all build it. If you read R173409 off an old cartridge or found it in your manual, any of the numbers below drops into the same housing.
Fitment notes
3-inch top and bottom openings. Hayward Star-Clear C500.
What to buy instead
Replacements for the Pentair R173409
Each button searches Amazon for one of the numbers this cartridge is sold under. The OEM version is usually the most expensive of the set and the aftermarket versions are the same physical filter, so it is worth checking all of them before you order.
Every number for this filter
| Brand | Part Number | Type |
|---|---|---|
| Pentair | R173409 | The number you searched |
| Pleatco | PA50 | Aftermarket equivalent |
| Unicel | C-7656 | Aftermarket equivalent |
| Filbur | FC-1240 | Aftermarket equivalent |
| Hayward | CX500-RE | Other OEM number |
| Purex | 27-079 | Other OEM number |
Full specs, the cartridge diagram, and the complete compatibility list live on the PA50 cartridge page. You can also see every 7″ × 19.625″ cartridge if you are checking a measurement rather than a part number.
Equipment that uses this cartridge
Looking for a different model? Browse every Pentair model we cover.
Frequently Asked Questions
What filter replaces the Pentair R173409?
The PA50 replaces it directly, and so does every cross-reference for it: C-7656, FC-1240. All of them are the same 50 sq ft cartridge at 7" outer diameter and 19.625" long. Buy whichever is cheapest at the time with solid recent reviews. The same cartridge also shows up as Hayward CX500-RE, Purex 27-079, so those are not different filters either.
Is the Pentair R173409 the same as the PA50?
Yes, physically the same filter. Pentair R173409 is an OEM number, meaning it is the code Pentair put on the cartridge that shipped with the equipment. Pentair does not manufacture cartridges. Pleatco, Unicel, and Filbur do, and they sell the identical part under their own numbers at a lower price. Match the dimensions against your old cartridge before ordering and you are covered.
Do I have to buy the Pentair version?
No. Nothing about the housing requires an OEM-branded cartridge, and the warranty on your equipment is not voided by using an aftermarket filter that meets the same spec. The reason to buy OEM is convenience, not performance. The reason not to is price, which is often a meaningful gap for an identical part. What matters is that outer diameter, length, and end-cap style all match.
What size is the Pentair R173409?
7 inches in outer diameter, 19.625 inches long, with 50 square feet of filter media. Both measurements need to land within about an eighth of an inch, and the end caps have to match so the cartridge seats correctly when you close the lid. Measure your old one rather than trusting a number that has worn off the label.
Data updated July 2026