Pentair 25" Bottom Tank Half Kit

The Pentair $1.25" \times .25"$ System:3 Air Relief Nipple O-Ring (part number 35505-1423Z, 35505-1423, or 355051423) is a high-performance elastomeric sealing component engineered explicitly for the manual and automatic air-purging assemblies of large-format filter vessels. This genuine original equipment manufacturer (OEM) part is standard hardware across Pentair's robust Sta-Rite System 3 filter lineup, providing critical pressure seals for the System 3 Modular Media SM Series, System 3 SD/SMD Series Diatomaceous Earth (D.E.) filters (models S7D75, S8D110), and System 3 SS Series High-Rate Sand filters (models S7S50, S8S70).

Engineering Dimensions & Specifications

Manufactured to standard Parker 2-318 industrial dimensional specifications, this robust O-ring features a nominal section profile of $1.25" \times 0.25"$ tailored for pool pad interfaces. Its precise manufacturing metrics provide a tight mechanical fit inside the designated compression channel of the upper tank’s air relief bulkhead fitting or plastic integration nipple.

• Material Composition: Formulated from a premium 70-durometer Nitrile Butadiene Rubber (NBR / Buna-N) compound.

• Durometer Hardness: The 70 Shore A rating represents the optimal balance between material flexibility needed for a localized fluid seal and structural rigidity required to resist extrusion.

Primary Operational Role

The primary function of this O-ring is to establish a leak-proof compression boundary at the high-velocity air-exhaust interface of the filter dome. Placed over the air relief nipple or bulkhead attachment, it undergoes tight compression when the external venting assembly is tightened down. This secure seal eliminates low-grade weeping or fine pressure leaks, which can allow air to bypass the system or cause the filter tank to slowly lose pressure. By ensuring an absolute fluid and airtight seal, the O-ring maintains the structural pressure dynamics of the primary tank shell, enabling the system to safely handle high circulation velocities and continuously sustain operating parameters up to 50 PSI without failing under sudden pump startup surges.

Material Resiliency

Built to endure the demanding conditions of an outdoor pool equipment pad, the high-density Buna-N compound offers outstanding tear resistance, low compression set (preventing the seal from permanently flattening over time), and dimensional stability through intense seasonal thermal shifts. It is highly resistant to degradation from chemical vapors and continuous exposure to common pool treatment chemicals, including liquid chlorine, bromine, algaecides, and acidic scale-removing flushes. Due to its compact structural size and dense rubber core, this individual replacement air relief nipple O-ring carries a nominal product and net shipping weight of approximately 0.02 to 0.05 pounds (about 0.32 to 0.80 ounces).