Pentair Purex 1/4″ Stainless Steel Split Lock Washer, 2 Required, 72172Z

Purex 72172Z is a 1/4 inch stainless steel split lock washer, and two are required wherever it is called out. It is small, cheap hardware that turns up on a lot of parts diagrams: Purex CFW cartridge filters, Purex 4000 Series molded DE filters, Pentair SM and SMBW 2000 Series backwash valves and Pentair EQ Series commercial pumps.

Why the washer matters

A split lock washer works by springing open against the nut as it is torqued down. The cut ends dig in and stop the fastener walking loose under the constant low frequency vibration a pump puts through a filter bank. Once the split has been crushed flat, or the washer has corroded, it no longer does that job and the nut it sits under starts to loosen between service visits.

Stainless, not plated

Stainless matters here more than it does indoors. Equipment pad hardware lives in splash, condensation and chlorinated air, and plated washers rust to the stud until the next technician has to cut them off. Replace the pair whenever you have the assembly apart rather than reusing crushed originals.