The Unicel 4CH-925 is a compact 20 square foot top-load replacement cartridge for select Strong Spas and Futura Antigua models. At just 7-1/4″ tall and 4-5/8″ across, it is one of the smallest threaded cartridges Unicel builds — and it packs 190 pleats into that short body, the densest fold-per-inch of any cartridge in its diameter class.
The bottom carries an injection molded 1-1/2″ SAE thread, with a semi-circular handle across the closed top. Molding the thread rather than machining it holds the form to a tighter tolerance and gives the connection a better chance of surviving the two dozen or so on-and-off cycles a cartridge sees over its life.
Getting the thread right is the whole ballgame here. SAE is a different standard from MPT pipe thread, even at the same nominal 1-1/2″ size — SAE is coarse and straight-sided, MPT is fine and slightly tapered. They will not interchange, and there are cartridges of nearly identical diameter and length built with each. Fortunately, on this particular cartridge there is an easier tell than the threads, and it is sitting right on top.
What the threaded design buys you is the elimination of bypass. On a drop-in cartridge the seal depends on the filter seating flat against a surface, and any gap lets unfiltered water slip past the media. Here the cartridge is the connection — water cannot reach the pump without passing through the media, because the only route into the suction line runs through the inside of the cartridge.
Media is 3 oz Reemay 2033 spunbonded polyester over a solid molded core, with chemical-resistant end caps. Made in the USA by Meissner Manufacturing, with more than 45 years behind the Unicel name.
Pro Tip — look at the handle. You will not need a tape measure. There is a closely related cartridge with the same 4-5/8″ diameter, a nearly identical length, and a bottom connection also described as “1-1/2 inch.” Measuring will not separate them confidently. But the two ends give it away instantly. This cartridge has a semi-circular handle — a rounded bar spanning the closed top — and a coarse SAE thread. The other has a molded cone handle, a tapered cone shape rather than a bar, and a fine MPT pipe thread. Glance at the top of your old cartridge. Bar means this one; cone means the other. Then confirm with the threads: coarse and straight-sided is SAE.
Brand
UNICEL®
