The multiport valve is the six-position selector that turns a sand or DE filter into a multi-purpose machine. Most techs learn two positions (Filter and Backwash) and bluff the rest. Learn all six, know when each is appropriate, and you'll solve problems the average pool guy can't diagnose.
The six positions and what each one does
| Position | Flow path | Use |
|---|---|---|
| Filter | Pump → top of filter → through media → back to pool | Normal operation. Where the valve lives 99% of the time. |
| Backwash | Pump → bottom of filter → reverse flow through media → waste line | Sand and DE only. Cleans the media. Never on a cartridge filter. |
| Rinse | Same as Filter, but discharges to waste for 20–30 seconds | Runs after backwash to settle media and flush fines out of waste line before returning to pool. |
| Waste / Drain | Pump → bypasses filter entirely → waste line | Vacuum-to-waste for algae blooms or lowering water level. Saves the filter from a shock load. |
| Recirculate | Pump → bypasses filter → back to pool | Circulating chemicals without filtering. Useful after heavy flocculant additions. |
| Closed | No flow | Service only. Never run the pump against a closed multiport. A 30-second mistake blows the spider gasket. |
The inviolable rule: pump OFF before you move the handle
The spider gasket inside the multiport is what isolates the six channels. Moving the handle while the pump is running drags the gasket across pressurized water and shreds it. The failure mode is usually not immediate — the valve leaks across ports a few weeks later, sending backwash water to the pool or filtered water to the drain.
Slide valves vs. rotary valves
Multiports come in two mechanical designs:
- Rotary (lever-and-spring) — the traditional spider-gasket design. Most residential filters.
- Slide (push-pull) — a linear valve with a waferred cylinder, fewer positions (typically Filter and Backwash only), more common on large commercial sand filters. Slide valves tend to last longer but give up the versatility of rinse, waste, and recirculate.
A real-world backwash sequence
- Pump off. Wait 10 seconds for pressure to bleed.
- Rotate to Backwash.
- Pump on. Run until sight glass runs clear (usually 2–3 minutes).
- Pump off. Rotate to Rinse.
- Pump on for 20–30 seconds.
- Pump off. Rotate back to Filter.
- Pump on. Record the new clean filter pressure on the log. That number— not a calendar — is how you decide when to backwash next. Back wash again when pressure rises 8–10 psi above the clean baseline.
Never skip the rinse. Skipping sends the stirred-up waste-line sediment right back to the pool and gives you a cloudy pool after what should have been a cleaning.