Piston Downflow ASY for Clack WS1 pn V3011 for Clack WS1 Valve and other "brands" that use the Clack type of valve under their private label.
Note: The Down Flow Piston ( V3011 ) is used when the control valve is uses a down flow softener ( most common ), OR Regenerating Filter ( such as Greensand application ), or Non-Regenerating filter ( this is Back Wash Only with just water through the tank... used with Carbon, Calcite, BIRM, and other "media" that is not "recharged" by salt or other chemicals ).
* WARNING: Do NOT lubricate this assembly. Internal o-rings are silicone, and the tolerance is already "tight". Adding any lubricant can cause the piston to "bind", and also "pull out" and damage o-rings. Also, these o-rings are NOT sold separately. So if you damage the Spacer Stack Assembly, you have to replace the entire Assembly.