PSR50-4 / UHD-SR50
50 sq ft replacement filter cartridge • 8.6875″ OD × 18.1875″ long
The PSR50-4 fits Sta-Rite's Posi-Flo 50TX and Swim-Thru filters, a 50-square-foot cartridge about 8-11/16 inches across and 18 inches tall. Sta-Rite part numbers include 50TX, 50TXR, T-50TX, and PTM50, and the Unicel cross-reference is UHD-SR50. There's no Filbur listing for this one, so your replacements are the Pleatco or a Sta-Rite OEM cartridge. One thing catches people out here: the 50TX and the higher-capacity 70TX use an identical-size can. Same diameter, same height. The 70 simply packs in more filter media. So matching physical dimensions isn't enough between these two. Check whether your tank is a 50 or a 70 first.
Compare on Amazon
PSR50-4 replacements on Amazon
The buttons below pull up Amazon results for each cross-reference part number. Same physical cartridge, different stickers, often different prices. Cross-shop and pick the cheapest option that has solid recent reviews.
Cross-Reference & Interchangeable Part Numbers
| Brand | Part Number | Type |
|---|---|---|
| Pleatco | PSR50-4 | Primary |
| Unicel | UHD-SR50 | Equivalent |
| OEM | Sta-Rite 50TX | Original Equipment |
| OEM | Sta-Rite 50TXR | Original Equipment |
| OEM | Sta-Rite T-50TX | Original Equipment |
| OEM | Sta-Rite PTM50 | Original Equipment |
Always verify dimensions and end-cap type before purchasing a replacement.
Compatible Pool Filter Systems
| Brand | Model |
|---|---|
| Sta-Rite | Posi-Flo 50TX |
| Sta-Rite | Swim-Thru 50 |
Frequently Asked Questions
What are the dimensions of the PSR50-4?
The PSR50-4 is 8.6875 inches in outer diameter, 18.1875 inches long, with an open top and an open bottom. Total filtration area is 50 square feet. Before ordering, pull your existing cartridge and measure it yourself, or check the label inside the housing. OD and length both have to match within about an eighth of an inch, and the end-cap style needs to match exactly so the cartridge seats properly when the lid closes.
What other part numbers are interchangeable with the PSR50-4?
PSR50-4 is the same physical cartridge as UHD-SR50, plus OEM versions like Sta-Rite 50TX, Sta-Rite 50TXR, Sta-Rite T-50TX, Sta-Rite PTM50. Same dimensions (8.6875" × 18.1875"), same open top, same open bottom. The Pleatco, Unicel, and Filbur boxes ship the same media inside, just with different stickers. The only thing to watch is the end-cap style: if a cross-reference has a slightly different cap design, it may not seat right in your housing.
Is the Sta-Rite 50TX the same filter as the PSR50-4?
Yes. Sta-Rite 50TX is an OEM number, the code the tub or pool builder stamps on the cartridge they ship. The filter itself is made by Pleatco, Unicel, or Filbur, so Sta-Rite 50TX (along with Sta-Rite 50TXR, Sta-Rite T-50TX, Sta-Rite PTM50) and PSR50-4, UHD-SR50 all point to one interchangeable cartridge. Buy whichever is cheapest with solid recent reviews, and just check that the dimensions match your old cartridge before you order.
How often should I replace the PSR50-4?
At 50 sq ft the PSR50-4 runs smaller than the big 100-plus sq ft pool cartridges, so it has less buffer between cleanings. Expect 12 to 18 months in normal use, less if the pool sees heavy traffic or the chemistry drifts. Watch the gauge: when pressure sits 8 to 10 psi above the clean starting point and a soak won't drop it, put in a fresh one.
How do I clean the PSR50-4?
The PSR50-4 has open ends on both top and bottom, so water flows straight through. Pull the cartridge from the housing and hose it down. Hit the pleats from above at about a 45-degree angle so water rinses debris out instead of packing it deeper, and work top to bottom while rotating the cartridge. Skip the pressure washer. The high pressure tears or collapses pleats, and once that happens you've lost media that doesn't come back. Every few months, give it a deeper clean: soak in a dedicated pool filter cleaner per the product's dwell time, then rinse it down completely before reinstalling. Keeping a spare cartridge on the shelf is genuinely worth it. You swap, run the soak overnight, and the pool keeps filtering.
Which hot tubs and spas use the PSR50-4?
Pull your existing cartridge and read the part number off the end cap, or check the label inside the filter compartment. That's the most reliable way to confirm compatibility.
Dimensions
Specifications
| Outer Diameter | 8.6875″ |
|---|---|
| Length | 18.1875″ |
| Top Type | Open (no end cap) |
| Bottom Type | Open (no end cap) |
| Filtration Area | 50 sq ft |
| Primary Brand | Pleatco |
| Part Number | PSR50-4 |
Fitment notes
Sta-Rite Posi-Flo 50TX / Swim-Thru series.