Waterway Plastics OEM 817-2500 spa filter (C-4326)

Top load 25

Replacement numbers

Unicel C-4326, Pleatco PRB25-IN

Fits Waterway Plastics OEM 817-2500.

Diameter 4-15/16" (125 mm)Length 13-5/16" (338 mm)25 sq ft

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UnicelC-4326
PleatcoPRB25-IN (Spec table PDF p.32: PRB25-IN, 5" x 13-5/16", open 2-1/8", 25 sq ft, OEM list includes 817-2500.)
FilburFC-2375
Top2-1/8" (54 mm) open
Bottom2-1/8" (54 mm) open
Ø 4-15/16" (125 mm)13-5/16" (338 mm)Side view · end views belowTopBottom
Top: 2-1/8" (54 mm) open
Bottom: 2-1/8" (54 mm) open
Drawn to scale from the listed diameter and length and open-end sizes. Handles, threads and closed ends are drawn as symbols, not to scale. 25 sq ft media.

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Waterway Plastics files this cartridge as C-4326 cartridge (OEM 817-2500), in the Top load 25 group. Numbers on the row: OEM 817-2500; Unicel C-4326; Pleatco PRB25-IN; Filbur FC-2375. 4-15/16" across, 13-5/16" long, top 2-1/8" open, bottom 2-1/8" open, 25 sq ft.

What the sources add about 817-2500: 25 sq ft open top-load. Unicel: 4-15/16" x 13-5/16", open 2-1/8", 106 pleats, 25 sq ft. Pleatco PRB25-IN lists OEM 817-2500 at 5" outside diameter and the same length. Filbur prints this OEM on two rows: FC-2375 at 13-5/16" (PRB25-IN, C-4326) and FC-2910, which the size table lengths at 13-1/4" and the Waterway section lengths at 12-1/4", with no Pleatco number. The size stored here is Unicel's. The 50 sq ft cartridge of the same length is 817-5000.

C-4326 (OEM 817-2500), Pleatco side: Spec table PDF p.32: PRB25-IN, 5" x 13-5/16", open 2-1/8", 25 sq ft, OEM list includes 817-2500..

817-2500, Filbur note: Waterway section PDF p.28: FC-2375 at 13-5/16" and FC-2910 at 12-1/4", both OEM 817-2500 and Unicel C-4326. Size table: FC-2910 at 13-1/4"..

Hold C-4326 next to C-4950 differs by Unicel C-4950, Pleatco PRB50-IN, Filbur FC-2390, 50 sq ft, OEM 817-5000, note says 50 sq ft open top-load. Same outside size as 817-2500. Unicel's spec note calls C-4950 an upgrade of the 25 sq ft C-4326: 212 pleats against 106, same 4-15/16" x 13-5/16" body. Pleatco PRB50-IN lists OEM 817-5000 at 5" outside diameter. Filbur FC-2390 agrees with Unicel's size and 50 sq ft. Waterway's table calls 817-5000 a 50 sq ft in-line top-load cartridge.; 4CH-926 differs by Unicel 4CH-926, Pleatco PWW25L, Filbur FC-0168, 13-1/2" long, top v-groove handle, bottom 2" female SAE, OEM 817-4025, note says Teleweir 25. Unicel and Waterway's table agree: 4-15/16" x 13-1/2", 25 sq ft, SAE thread. Unicel's spec table says 2" female SAE, 105 pleats, for a 1-1/2" male SAE standpipe (the standpipe note is printed on the 4CH-935 and 4CH-949 spec lines). Pleatco PWW25L is 5" x 13-3/16", 1-1/2" female SAE, 25 sq ft, and that spec line does not print 817-4025. The cross-reference does: 4CH-926 = PWW25L. Filbur FC-0168 is 13-1/16" long and 1-1/2" female SAE. Same length as 817-4050, half the area..

Left blank on purpose: Outside diameter 4-15/16" vs Pleatco 5". Filbur FC-2910 length 13-1/4" in the size table and 12-1/4" in the Waterway section, against 13-5/16" on FC-2375, Unicel, and Pleatco..

Source locations for this Waterway Plastics row: Unicel 2026 Replacement Guide on C-4326 (Waterway list PDF p.64: 817-2500 = C-4326, 4-15/16" x 13-5/16", 25 sq ft. Spec table PDF p.9: open 2-1/8", 106 pleats.). Waterway Plastics Service Logic cartridge table on C-4326 (Fetched 2026-11-09: 817-2500, 25 sq ft, in-line top-load). Pleatco 2023 Catalog on C-4326 (Spec table PDF p.32: PRB25-IN includes OEM 817-2500, 5" x 13-5/16", 25 sq ft). Filbur Catalog & Reference Guide on C-4326 (Waterway section PDF p.28: FC-2375 and FC-2910 both list OEM 817-2500. Size table lengths FC-2910 at 13-1/4".).

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Measure diameter, length, and both ends, then compare them with the figures above. The steps are in the measuring guide. Why the bottom decides whether it seals: open-end vs threaded filters. Power, the retainer, and not running the spa empty: how to install a cartridge. Number formats: how Filbur, Unicel and Pleatco numbers compare.

The same C-4326 number is also on the Hot Spring, Hot Spot, Jacuzzi, Beachcomber, PDC Spas pages.

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Sources

Not in sources: Outside diameter 4-15/16" vs Pleatco 5". Filbur FC-2910 length 13-1/4" in the size table and 12-1/4" in the Waterway section, against 13-5/16" on FC-2375, Unicel, and Pleatco..