Darlly 40371 Spa Filter Cartridge
Replaces Unicel C-4637 · Pleatco PRB37-IN (now ULTRA-S5) · Filbur FC-2380
- Diameter × length
- 4-15/16" × 13-5/16"
- Filter area
- 37 sq ft
- End caps
- 2-1/8" Open / 2-1/8" Open
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 40371 is a 37 sq ft spa filter cartridge, 4-15/16" x 13-5/16". It replaces Unicel C-4637, Pleatco PRB37-IN (now ULTRA-S5) and Filbur FC-2380.
Specifications
| Darlly part number | 40371 |
|---|---|
| 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 | 37 sq ft |
| Type | Spa |
| Darlly description | Rainbow, Waterway Plastics, Morgan Spas. Leisure Bay Spas. Custom Molded Products |
Cross-reference
| Brand | Part numbers Darlly 40371 replaces |
|---|---|
| Unicel | C-4637 |
| Pleatco | PRB37-IN (now ULTRA-S5), ULTRA-S5 |
| Filbur | FC-2380 |
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-4637?
- Darlly 40371 replaces Unicel C-4637. Both are 4-15/16" in diameter and about 13-5/16" long.
- What Darlly cartridge replaces Pleatco PRB37-IN?
- Darlly 40371 replaces Pleatco PRB37-IN, which Pleatco now sells as ULTRA-S5.
- What size is Darlly 40371?
- Darlly 40371 is 4-15/16" in outside diameter and 13-5/16" long, with 37 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.