Clack WS2 and WS2QC Service Kit (Stack and Pistons) Backwashing

The Clack WS2 and WS2QC Service Kit for the backwashing cycle piston is a genuine stack and piston rebuild kit for the larger commercial-size WS2 and WS2QC control valves, and WrekinWater stocks it for installers and site engineers maintaining Clack-based commercial softeners and filters across the UK. Rather than replacing the whole valve, this kit renews the wearing stack seals and piston that drive the backwashing stage of the regeneration cycle, restoring correct operation at a fraction of the cost of a full valve swap.

Technical specifications

Symptoms that mean you need this part

• The valve weeps or drips water from the drain line outside of a backwash cycle
• The valve sticks, stalls or fails to complete the backwash stage of regeneration
• You hear grinding, knocking or unusual resistance as the piston tries to shift position
• A visible drop in system flow or pressure that coincides with erratic backwash cycling

Why it fails / why it matters

The stack and piston assembly is the part of a Clack WS2/WS2QC valve that physically moves to open and close the internal ports during each stage of regeneration, and on the backwashing stage in particular it's under constant flow and pressure that gradually wears the rubber seals and scores the piston shaft. Once the seals harden or the piston surface pits, water bypasses where it shouldn't, the piston can stick partway through its travel, and the valve either leaks to drain continuously or fails to complete a clean backwash — both of which point to a worn stack and piston rather than a fault elsewhere in the valve.

Why buy this from WrekinWater

WrekinWater has served more than 50,000 customers over 15 years from its base in Bettisfield, Shropshire, and stocks genuine Pentair Fleck, Autotrol, Clack and Kinetico spares including this WS2/WS2QC backwashing service kit, so installers can keep commercial valves running with the correct parts rather than an approximate substitute. As UK Company No. 11000488 and rated Excellent on Trustpilot, the team can help confirm this is the right cycle kit for your valve before you order.

How to fit it

1. Isolate the water supply and relieve system pressure, then place the valve in bypass if fitted
2. Remove the valve's top cover or cap screws to access the stack and piston assembly
3. Withdraw the old piston and stack, noting the order and orientation of seals and spacers
4. Clean the bore thoroughly and inspect for scoring or debris before fitting new parts
5. Fit the new stack and piston from the kit, lightly lubricating seals with a food-grade silicone lubricant as specified by Clack
6. Reassemble the cover, restore water supply, and run a manual backwash cycle to confirm smooth piston travel and no leaks to drain