Cartridge models use a synthetic, spun-bond polyester material as the filtration medium. When water passes through the medium, the unique design of the fibers traps the debris. Finer particles are filtered out as the pores of the element become covered by the larger debris.

Cartridges for pools do not filter as finely as diatomaceous earth, which can go down to 1- to 6 microns. Instead, their abilities lie in the 5- to 20 micron range, while sand filters work in the 20- to 40 range (after cleaning; however, after half their filter run, they typically can filter in the range of 8- to 15 microns).

Cartridge filters do not have a backwash valve, which makes the hydraulics of the system fairly simple. More importantly, cartridge filters do not require additional plumbing to remove the waste water generated from backwashing. In fact, cleaning cartridge filters is a breeze. The cartridge element can be cleaned by pressure washing it in combination with the use of a filter cleaner. Just remove the cartridge elements, hose them off, soak them and then put them back into the tank.

Watch that gauge

Manufacturers have designed filters with enough surface area (300- to 600 square feet), so they only need cleaning once or twice each year. However, as with all types of filter media, you can determine the need for service with cartridges by watching the tank pressure gauge.

Whenever you replace a filter element, observe the start-up pressure on the tank gauge, indicated in pounds per square inch (psi).

Some manufacturers now provide a convenient dial on the pressure gauge for monitoring pressure levels. If that is not available, take a grease pencil or magic marker and draw a line on the face of the gauge at that point, marking the “base-line” or “starting” pressure.

Now mentally add 8- to 10 psi to the reading and make another little mark accordingly on the gauge.

The space between those two marks is the “normal operating pressure” for that cartridge filter system.

As long as the filter operates between those two marks, all is generally well. Clean when the pressure gauge hits the higher mark. To simplify things, add the cartridge-filter readings to your own records or route sheet.

Note: If you let the filter go too long before cleaning, you will blind-off pleats and can even collapse the filter element. This will result in a damaged filter, which will need to be replaced.

Dirt can be a good thing

While it may seem contradictory to its purpose, a somewhat dirty cartridge is actually more efficient than a clean one, say cartridge manufacturers. Why? Because the dirt that accumulates on filter fibers makes the filter material an even tighter web, capturing finer particles than it could when clean. At this point, the trapped dirt is basically working like the diatomaceous earth does in a DE filter.

That is not to say that cartridge filters don’t need cleaning, of course. Rather, it’s to make the point that a brand-new element is not as effective at removing debris from the water as one that’s more “seasoned.”For pools with heavy bather loads or other conditions hostile to effective filtration, some technicians prefer replacement rather than cleaning. It’s a judgment call.

Carrying a spare cartridge or two in your truck may come in handy. That way, you can replace the customer’s cartridge while taking the old one in for a more thorough cleaning.

Note: Richard Howell, the former national sales manager at Filbur Manufacturing and current vice president of sales, pool division for Waterway Plastics, contributed to this article.