Waterway Plastics OEM 817-7500 spa filter (C-4970)

Top load 75, discontinued by Unicel

Replacement numbers

Unicel C-4970, Filbur FC-2930

Fits Waterway Plastics OEM 817-7500.

Diameter 4-15/16" (125 mm)Length 23-5/8" (600 mm)75 sq ft

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UnicelC-4970
Pleatconot found in source (Deactivated list PDF p.21: PCAL75 replacement PCAL100. No 817-7500 and no C-4970 in the 2023 spec table or Unicel cross-reference.)
FilburFC-2930
Top2-1/8" (54 mm) open
Bottom2-1/8" (54 mm) open
Ø 4-15/16" (125 mm)23-5/8" (600 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. 75 sq ft media.

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Top load 75, discontinued by Unicel is the group name on the Waterway Plastics row C-4970 cartridge (OEM 817-7500). Match these numbers: OEM 817-7500; Unicel C-4970; Filbur FC-2930. 4-15/16" across, 23-5/8" long, top 2-1/8" open, bottom 2-1/8" open, 75 sq ft.

What the sources add about 817-7500: 75 sq ft top-load. Unicel's Waterway line prints 817-7500 = C-4970 at 75 sq ft and says C-4970 is discontinued: use C-4995. C-4995 is 817-1000, which Unicel rates at 95 sq ft, so the named replacement is not a 75. Waterway's current table still lists 817-7500 at 75 sq ft. Filbur FC-2930 still prints C-4970, PCAL75, and 817-7500 at 75 sq ft. Pleatco's deactivated list sends PCAL75 to PCAL100 and does not print 817-7500. PCAL100 is not stored here; it is the equivalent on the 817-1000 row.

C-4970 (OEM 817-7500), Pleatco side: Deactivated list PDF p.21: PCAL75 replacement PCAL100. No 817-7500 and no C-4970 in the 2023 spec table or Unicel cross-reference..

817-7500, Filbur note: Waterway section PDF p.28: FC-2930, 4-15/16" x 23-5/8", OEM 817-7500, PCAL75, C-4970, 75 sq ft..

Before ordering C-4970, compare it with C-4995 differs by Unicel C-4995, Pleatco PCAL100, Filbur FC-2940, 95 sq ft, OEM 817-1000, note says The cartridge Unicel names in place of discontinued C-4970. Unicel's spec table and Waterway OEM line: 4-15/16" x 23-5/8", open 2-1/8", 222 pleats, 95 sq ft. That 95 is what is stored. Waterway's own table calls 817-1000 a 100 sq ft in-line cartridge. Pleatco PCAL100 is 5" x 23-5/8", 100 sq ft, OEM 817-1000. Filbur's Waterway section prints FC-2940 at 100 sq ft, and another FC-2940 row prints 95. Same length as the 75 sq ft cartridge it replaces.; and 4CH-926 differs by Unicel 4CH-926, Pleatco PWW25L, Filbur FC-0168, 13-1/2" long, top v-groove handle, bottom 2" female SAE, 25 sq ft, 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..

Pleatco does not have a number on this row. Search 817-7500 or the Waterway Plastics part you pulled out of the spa.

Left blank on purpose: Unicel says to stop using this number. Waterway's table and Filbur still list it at 75 sq ft. The replacement Unicel names is a different area..

Where those figures are printed: Unicel 2026 Replacement Guide on C-4970 (Waterway list PDF p.64: 817-7500 = C-4970, 75 sq ft, 4-15/16" x 23-5/8", discontinued, use C-4995. Spec table PDF p.9: 178 pleats, same discontinued note.). Waterway Plastics Service Logic cartridge table on C-4970 (Fetched 2026-11-09: 817-7500 still listed, 75 sq ft, in-line top-load). Pleatco 2023 Catalog on C-4970 (Deactivated list PDF p.21: PCAL75 replacement PCAL100). Filbur Catalog & Reference Guide on C-4970 (Waterway section PDF p.28: FC-2930, OEM 817-7500, C-4970, 75 sq ft).

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Check the cartridge you removed

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.

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Sources

Not in sources: Unicel says to stop using this number. Waterway's table and Filbur still list it at 75 sq ft. The replacement Unicel names is a different area..