Darlly 40506 Spa Filter Cartridge
Replaces Unicel C-4950 · Pleatco PRB50-IN (now ULTRA-S5) · Filbur FC-2390
- Diameter × length
- 4-15/16" × 13-5/16"
- Filter area
- 50 sq ft
- End caps
- 2-1/8" Open / 2-1/8" Open
- Per filter
- 1 cartridge
Pool and spa businesses in Florida, Georgia, South Carolina, Alabama, Mississippi, Louisiana and Texas order through their Grit Game rep. Everywhere else, contact Darlly Filtration directly.
Darlly 40506 is a 50 sq ft spa filter cartridge, 4-15/16" x 13-5/16". It fits the Rainbow / Pentair Dynamic Series I RDC-50, II & III RTL/RCF-50, IV DFM/DFML and Waterway 50 in-line. It replaces Unicel C-4950, Pleatco PRB50-IN (now ULTRA-S5), Filbur FC-2390, Pentair R173434 and Pentair / Rainbow 17-2380.
Specifications
| Darlly part number | 40506 |
|---|---|
| Outside diameter | 4-15/16" |
| Length | 13-5/16" |
| Top end cap | 2-1/8" Open |
| Bottom end cap | 2-1/8" Open |
| Filter area | 50 sq ft |
| Type | Spa |
| Blue antimicrobial version | 40506M |
| Darlly description | Rainbow, Waterway Plastics, Custom Molded Products (Wellis # AKU1831) |
Cross-reference
| Brand | Part numbers Darlly 40506 replaces |
|---|---|
| Unicel | C-4950 |
| Pleatco | PRB50-IN (now ULTRA-S5), ULTRA-S5 |
| Filbur | FC-2390 |
| Hurricane (former brand) | HF4950-01 |
| OEM and other numbers | Pentair R173434, Pentair / Rainbow 17-2380, Rainbow / Pentair / Waterway RTL-50, Waterway 817-5000, Sundance 6540-471 |
Filters it fits
| Filter | Cartridges per filter | OEM cartridge number |
|---|---|---|
| Rainbow / Pentair Dynamic Series I RDC-50, II & III RTL/RCF-50, IV DFM/DFML; Waterway 50 in-line (50 sq ft filter) | 1 | R173434, 17-2380, RTL-50, 817-5000, 6540-471 |
Other Darlly cartridges the same size
Same diameter and length. Check the end caps and area before swapping.
Questions
- What is the Darlly replacement for Unicel C-4950?
- Darlly 40506 replaces Unicel C-4950. Both are 4-15/16" in diameter and about 13-5/16" long.
- What Darlly cartridge replaces Pleatco PRB50-IN?
- Darlly 40506 replaces Pleatco PRB50-IN, which Pleatco now sells as ULTRA-S5.
- What size is Darlly 40506?
- Darlly 40506 is 4-15/16" in outside diameter and 13-5/16" long, with 50 sq ft of filter area.
Cross-reference checked October 21, 2026 against Unicel's 2026 Replacement Guide, Pleatco's catalog (updated September 2025), filbur.com and darllyfilter.com. A competitor number is listed only when that brand's own data pairs it with the same cartridge size. Always compare the size and end caps of your old cartridge before ordering.
Brand names and part numbers are trademarks of their respective owners and are shown only to identify compatible replacements. Darlly Filtration is not affiliated with or endorsed by them. Cross-reference by The Grit Game, Darlly's sales agency.