Clack vs Fleck Water Softener Valves, Explained
The control valve is the "brain" on top of a softener tank. It decides when to regenerate, meters your water use, and moves water through backwash, brine draw, rinse and refill. Many independent installers build systems around one of two third-party valves: the Clack WS1 (made by Clack Corporation in Windsor, Wisconsin) or a Pentair Fleck valve, most often the 5600SXT on homes and the 2510 on bigger tanks. Both are standard, widely documented parts, which is why a quote naming one of them is easier to check and service than a proprietary box.
Every number below comes from the manufacturers' own spec sheets and service manuals (linked at the bottom).
Side-by-side: Clack WS1 vs Fleck 5600SXT
| Spec | Clack WS1 (1") | Fleck 5600SXT |
|---|---|---|
| Service flow | 27 gpm @ 15 psi drop, measured with meter and bypass installed | 20 gpm continuous @ 15 psi drop (valve alone); 26 gpm peak @ 25 psi drop |
| Max backwash flow | 27 gpm @ 25 psi drop (with bypass) | 7 gpm @ 25 psi drop |
| Softener tank diameters | 6" to 21" | 6" to 12" |
| How the piston moves | Screw-driven piston; position counted by an optical sensor, no cams or switches | "Time-tested, hydraulically balanced piston" per Pentair |
| Regeneration modes | Meter immediate, meter delayed, or time clock delayed; days override 1 to 28 | Immediate meter, delayed meter, delayed time clock, or day-of-week |
| Cycles | Up to 6, with a double backwash | 5 adjustable (3- or 5-cycle), double backwash capable |
| Brine refill | Refills with softened (treated) water while in service, at 0.5 gpm | Refill as programmed in the cycle sequence |
| Power-outage memory | Settings in nonvolatile memory; coin-cell battery keeps time for about 8 hours | Settings kept in memory; super capacitor keeps time of day (about 48 hours per the spec sheet) |
| Operating pressure | 20 to 125 psi | 20 to 125 psi working |
| Water temperature | 40 to 110°F | 34 to 110°F (cold water valve) |
| Drain line | 3/4" or 1" NPT | 1/2" NPTF |
| Certifications listed | NSF/ANSI 44, NSF/ANSI/CAN 61 and 372 | WQA-certified to NSF/ANSI 44 and 372, CSA B483.1 |
| Bypass valve | Optional, sold separately (1" four-position with a diagnostic position) | Optional, sold separately (plastic or stainless) |
Clack measures service flow with the meter and bypass in place, while Fleck's 20 gpm figure is for the valve alone, so the two numbers aren't measured the same way.
What those numbers mean for a normal house
- Flow: both valves move far more water than a typical home uses at once, so for most single-family homes either is fine. Flow matters more for large homes with many bathrooms running at the same time.
- Backwash is the real difference. Backwash lifts and cleans the resin bed. The 5600SXT's 7 gpm limit is why Fleck rates it for softener tanks only up to 12" wide. The Clack WS1 backwashes up to 27 gpm and covers tanks up to 21". If a quote puts a 5600SXT on a 13" or 14" tank, ask why.
- Tank size ties back to sizing. In our sizing guide, a family of 4 at 15 gpg with 1 ppm iron lands on a 10" × 54" tank, which is within range for both valves.
- Metered vs timer: both can regenerate based on gallons actually used (metered), which usually saves salt and water versus a fixed timer. Ask that the valve be set to a metered mode.
Bigger Fleck and Clack options
If your quote names a different model, here's how the bigger valves compare, per Pentair and Clack:
| Valve | Service flow | Backwash | Softener tanks |
|---|---|---|---|
| Fleck 2510 (SXT discontinued; replaced by 2510 AiQ) | 19 gpm @ 15 psi drop | 17 gpm @ 25 psi drop | Up to 16" |
| Clack WS1.25 | 32 gpm @ 15 psi drop (with meter and bypass) | 30 gpm @ 25 psi drop | Uses a 1.32" distributor; check the Clack manual for tank range |
Pentair lists the Fleck 2510 SXT as discontinued and points buyers to the 2510 AiQ. If a dealer quotes a "new" 2510 SXT, ask whether it's leftover stock and whether parts and warranty still apply.
Which one should you pick?
Neither is a scam or a downgrade. The better question is who will service it:
- Pick the valve your installer stocks parts for and is willing to service locally.
- For tanks wider than 12", or if you want more backwash headroom (for example on well water with sediment), the Clack WS1 or a larger Fleck like the 2510 AiQ is the spec-sheet fit, not the 5600SXT.
- For a small to medium home on city water with a 12" or smaller tank, a 5600SXT is within its rated range.
- Both valves' manufacturers publish their manuals openly, so a handy homeowner or any independent tech can find replacement parts. That's the main advantage over a dealer-only proprietary valve.
Questions to ask on any quote
- What exact valve model is it, and is it metered?
- What tank diameter and resin volume (cubic feet) is it on, and is that within the valve's rated tank range?
- Is a bypass valve included? (Both brands sell it separately.)
- Who supplies parts and service if your company is gone in five years?
- What salt setting per regeneration will you program? (See the capacity vs salt table.)
Sources
- Clack Corporation: WS1 Control Valve specifications
- Clack: WS1 Water Specialist spec sheet (Form 2572)
- Clack: WS1 and WS1.25 Drawings and Service Manual
- Pentair: Fleck 56SXT Control Valve spec sheet
- Pentair Fleck 5600 spec sheet (42749 Rev E, hosted by Pure Aqua)
- Pentair: Fleck 2510 SXT (discontinued)
- Pentair: Fleck 2510 AiQ Valve
Next: Water Softener Quotes Decoded (real installed prices)