A leaking filter is not one problem. Depending on where the water appears, it is one of three quite different seals — and they are not interchangeable.
1. The lid or head o-ring
Cartridge filters seal at the top where the lid clamps down. Symptoms: water escaping around the lid rim, especially when the pump starts and pressure rises.
This is the seal that gets disturbed at every cartridge clean, which is why it is the one that fails most.
2. The tank band / body o-ring
Larger filters split into two halves held by a clamp band. Symptoms: water weeping from the seam all the way round, often only under pressure.
Pentair 71441 tank o-ring, CF-25, CF-50 and 700
People overtighten the band trying to stop this. It rarely works — the o-ring seals, the band only holds the halves together. Excess force distorts the flange and makes the next repair harder.
3. The valve seals
Where the multiport or Vari-Flow valve joins the tank. Hayward SPX710XZ3 Vari-Flow lid o-ring, after 1976 — note the date qualifier, because Hayward changed this part and the earlier one is different.
If water is escaping to waste rather than outside the unit, that is a valve internal problem, not a leak — see our multiport valve guide.
Sand and DE filters have union seals too
Modular media systems like the Sta-Rite and Pentair System:2 and System:3 use union o-rings at the plumbing connections, such as U9-362. Those are a common slow-drip source that gets blamed on the tank.
A note on date qualifiers
Several filter seals carry them — "after 1976", "pre-1998". Manufacturers revised tooling and the parts are genuinely different. If a listing specifies a date range, it matters. When you are unsure how old your equipment is, send us the model number rather than guessing.
Before you reassemble
Seat every o-ring with a thin film of food-grade silicone. Dry rings pinch and take a set — the usual reason a new seal weeps within a season. Aqua Flex Food Grade Silicone Lubricant is what ships in our kits.
O-rings only. Never lubricate the polished faces of a mechanical shaft seal.
Beaver Island Parts Company is not affiliated with, endorsed by, or sponsored by any equipment manufacturer named on this page. All brand names, model numbers and part numbers are the property of their respective owners and are used solely to identify the equipment our replacement parts fit.