Choose a Well-Water Spin-Down Filter by Sediment, Flow and Pressure Loss

A spin-down sediment filter for well water is a useful first stage when the supply carries sand, grit or other solid particles. Its reusable screen and bottom flush valve let you discharge collected sediment without replacing a cartridge each time. The right choice depends on particle size, operating flow and allowable pressure loss—not simply the pipe connection size.

It is not a cure for a well that has suddenly started pumping sand, and a filter downstream of the well pump cannot protect that pump from grit it has already handled.

What it catches—and what it does not

In a typical spin-down design, incoming water swirls around a screen. The swirling motion helps separate debris into the lower collection area, while the screen intercepts particles. Opening the bottom valve flushes collected solids out under system pressure. Rusco’s Sediment Trapper design adds collection space below the screen. See the manufacturer’s spin-down and sediment-trapper guide.

This makes a spin-down worth considering when coarse debris is loading a finer downstream filter. Very fine silt may pass through a coarse screen or clog a fine one; a finer cartridge or another treatment arrangement may still be needed.

Do not treat a sediment screen as disinfection or dissolved-contaminant removal. Hardness, dissolved iron and bacterial contamination require treatment matched to water-test results. Penn State Extension distinguishes sediment filtration from softening, iron treatment and disinfection.

Investigate a new or increasing sand problem before merely adding filtration. Penn State lists increased sediment as a warning of deteriorating well or pump performance; possible causes include inadequate well development, overpumping, and screen or casing deterioration. A well contractor’s inspection addresses the source rather than just the debris reaching the house.

Choose the screen opening, not the smallest advertised number

For a screen, the micron figure describes its opening size; mesh describes the screen’s fineness. They are not interchangeable. Smaller micron openings are finer, whereas higher mesh numbers generally indicate finer screens.

For example, Rusco’s January 2026 guide gives these approximate openings:

Rusco screen mesh	Approximate opening
60 mesh	254 microns
100 mesh	152 microns
140 mesh	104 microns
200 mesh	74 microns
250 mesh	61 microns

These are manufacturer-specific mesh conversions, not a universal conversion table. In particular, 100 mesh is not 100 microns.

Rusco recommends choosing the coarsest screen that removes the sediment concerned. That is a better starting principle than assuming every well needs a 50-micron filter. Too coarse lets the target particles through; unnecessarily fine filtration increases the likelihood of frequent cleaning.

Identify the sediment and check the requirements of the equipment you intend to protect. If the spin-down is only a coarse prefilter, let the downstream stage handle smaller particles. Our sediment filter cartridge guide explains the next-stage choices.

Check both flow range and pressure loss

Size for the water that must pass through the filter at peak demand, including irrigation or treatment backwash if those flows use the same line. Ask for the pressure-loss curve for the actual body and screen, not just a maximum gallons-per-minute rating.

Bigger is not automatically better. Rusco’s guide lists minimum flows for its T-style spin-out action of 1 GPM for the 1-inch model, 10 GPM for the 1½-inch model and 18 GPM for the 2-inch model. Below those thresholds, do not assume the intended separation action occurs; the screen can still intercept particles. The guide also provides pressure-loss curves. These minimums are model-specific, not requirements for every flushable screen filter.

A restriction consumes pressure while water flows. A satisfactory reading at the tank therefore does not prove adequate pressure after a loaded filter. Where suitable gauge connections are available, compare inlet and outlet pressure during flow, then repeat at the same flow after cleaning. Record the clean-filter difference as a baseline. Follow any manufacturer-specified service limit; otherwise, use changes in pressure loss and delivered flow to judge when cleaning is needed rather than assuming a universal pressure-drop threshold.

Put it after the pressure tank and controls

For a conventional household well system, the usual arrangement is:

Well pump → pressure-tank connection, pressure switch and relief valve → spin-down prefilter → required downstream treatment → house

Do not put a clog-prone filter between a submersible pump and the pressure tank to “protect the tank.” Boshart explains that a blockage can isolate the tank-mounted pressure switch from pump discharge pressure: the pump keeps running because the switch cannot detect the pressure needed to shut it off. The tank-side relief valve also cannot release that upstream pressure. Its installation guidance calls for sediment filters after the pressure tank. Pentair likewise specifies after-tank placement for its FPS-10BB and FPS-20BB filter systems.

For a surface jet pump, do not casually add a fine screen to the suction line. Rusco’s user guide specifies discharge-side installation, where system pressure supports flushing. Nonstandard controls or treatment layouts need a system-specific installation plan.

Provide access for screen removal, a suitable place for flush water, and protection against freezing, impact and incompatible chemicals. Follow the flow arrow and mounting instructions, and verify the complete assembly’s pressure, temperature and potable-water suitability.

Flushing is maintenance, not a guarantee of cleanliness

Inspect frequently at first and set the flushing interval from actual sediment loading and the product instructions. An automatic flush valve changes who opens the valve; it does not eliminate screen inspection.

If flushing empties the bowl but flow remains poor, particles may be lodged in the screen. Rusco directs users to shut off the supply and relieve pressure before removing the cover, then rinse the element and use a soft brush for trapped fines. Its cleaning instructions require hand-tightening the cover.

A screen that immediately clogs again calls for reassessment of screen fineness, sediment load and the well itself—not a higher pressure-switch setting. If pressure remains weak after cleaning, continue with the well-pressure troubleshooting checks.