Hayward ProSeries Sand Filter

The ProSeries is the sand filter sitting beside a great many above-ground pools. It is a tall molded tank with a seven-position valve on top, and it comes in five diameters. The 18-inch S180T is the one this site shortlists, and Hayward describes it as high-capacity filtration for larger above-ground pools.

Hayward is not entirely consistent about where it belongs. The sell sheet keeps "small in-ground pools" for the 21-inch and up, and the Open Line W3S180T is listed for above-ground pools only — but the dealer S180T listing is tagged for in-ground pools as well. On an in-ground pool, the sell sheet's advice is the safer one to follow: start at the S210T rather than stretching the 18. Hayward also makes the ProSeries as a side-mount, in 24 and 30 inches, with the valve beside the tank instead of on top.

Size it by flow, not by pool

The filter does not care how many gallons you own. It cares how many gallons a minute your pump pushes through it. Hayward's design flow rates, from the 2025 sell sheet:

• S144T, 14 in. — 1.07 sq. ft., 25 GPM
• S166T, 16 in. — 1.40 sq. ft., 30 GPM
• S180T, 18 in. — 1.75 sq. ft., 35 GPM
• S210T, 21 in. — 2.20 sq. ft., 44 GPM
• S230T, 23 in. — 2.70 sq. ft., 54 GPM, and sold only as a system with a pump

On the 18, 21 and 23-inch tanks, flow divided by area comes out at exactly 20 GPM per square foot. The two smaller tanks are rated a little harder, at about 23 and 21. Either way the pattern holds: a bigger tank is mostly more sand bed at much the same speed of water. Work out what your pump actually moves, then pick the tank whose design flow sits at or above it.

The plumbing sets a ceiling too. The manual gives 45 GPM as the maximum for 1½-inch pipe, which is the valve size on the 18-inch. The S180T's 35 GPM sits comfortably under it.

If you are buying the filter and pump together, Hayward's 18-inch system is W3S180T93S, and Hayward lists its pump at 1.1 total horsepower. Some retail listings still describe that system as 1.5 HP. Go by Hayward's specification, not the listing title.

Loading the sand

The 18-inch takes 150 lb of No. 20 silica sand, graded 0.45 to 0.55 mm. The 14-inch takes 50 lb, the 16-inch 100 and the 21-inch 200. Use the grade Hayward specifies; the manual notes that filter sand is not all the same.

The manual's loading sequence is short, and every step protects something:

1. Cap the center pipe with the sand shield so no sand drops down it.
2. Check every lateral is folded down before anything goes in.
3. Fill the tank about halfway with water first. The water cushions the sand as it falls, so the laterals at the bottom are not hit by 150 lb of it.
4. Pour slowly, keeping the center pipe centered, and stop with the sand at least 10 inches below the top of the tank.
5. Put the valve back on with its o-ring in place, then tighten the flange clamp while tapping around it to seat the valve.

The halfway fill is the easy step to skip, and the laterals are what it protects. A cracked lateral shows itself as sand turning up on the pool floor.

Backwash at 8 to 10 psi over clean

Write down the gauge reading once the filter is clean and running. When it climbs 8 to 10 psi above that number, it is time to backwash. The clean reading varies from pool to pool, so no fixed number on the gauge means anything by itself.

Hayward's sequence:

1. Pump off. Press the handle down and turn it to Backwash.
2. Pump on, and run until the sight glass runs clear — about two minutes or less.
3. Pump off, handle to Rinse, pump on for about half a minute to a minute.
4. Pump off, handle to Filter, pump on.

Two rules sit under every step. The pump goes off before the handle moves, and the handle is pressed down before it turns — the second protects the valve's internal seal. The full backwashing guide covers the rest, including what to do with the waste water.

On a brand-new filter, Hayward wants the first run in Backwash for at least two minutes to flush fines out of new sand. The exception is a new plaster or gunite pool full of dust: start that one in Filter, so the debris does not clog the laterals from underneath.

What the positions do

Hayward calls the VariFlo a seven-position valve. The manual names these settings:

• Filter — normal running, and regular vacuuming
• Backwash — cleaning the sand
• Rinse — settling the bed after a backwash, so dirty water goes to waste rather than back to the pool
• Waste — bypasses the sand entirely, for lowering the water or vacuuming heavy debris straight out
• Recirculate — moves water through the pool system without filtering it
• Closed — shuts off flow from the pump to the filter

For winter, the manual does not use a position at all. It has you park the pointer between two positions so the valve can drain.

If the filter cycles short

When pressure climbs back fast after a backwash, the manual's checklist starts with the water, not the filter: look for algae and shock if needed, and bring chlorine and pH into range. After that it points at the sand itself. Check the top of the bed for a crust or caking, and if it is there, remove about an inch of sand.

Check the prefix before you buy

S180T and W3S180T are the same filter sold down two channels, and the letters decide the warranty:

• S180T, through a dealer — two years parts, no labor
• W3S180T, Hayward's Open Line for online sale — one year parts, no labor

Neither covers labor, so on this filter the choice is one year of parts against whatever the price difference is. The W3 route is a sanctioned purchase, not a void one — Hayward approves Open Line SKUs for online sale. The Hayward brand page explains the two channels.

Winterizing

Three steps from the manual. Unscrew the drain cap at the base of the tank and leave it off all winter. Set the valve pointer between any two positions so the valve drains. Then winterize the pump according to its own instructions.

Keep the cap somewhere you will find it in spring. The filter will not hold water without it.