Product Overview

The Sta-Rite 21" Tank O-Ring | 24850-0008 is a replacement tank seal designed for select Sta-Rite System:3 pool and spa filters with 21" tanks. This O-ring helps create a watertight seal between the upper and lower filter tank sections, helping prevent leaks and maintain proper filtration system pressure.

This part is commonly used with compatible System:3 modular media cartridge filters, System:3 D.E. filters, and System:3 sand filters. It is a critical replacement item when the existing tank O-ring becomes flattened, stretched, cracked, dry, or damaged.

Ideal For

• Sta-Rite System:3 filter maintenance
• Replacing worn tank O-rings
• Correcting filter tank leaks
• Restoring proper filter sealing
• System:3 cartridge filters
• System:3 D.E. filters
• System:3 sand filters
• Pool equipment pad service
• Filter cleaning and rebuild service
• Professional pool service technicians

Key Features

• 21" tank O-ring — designed for compatible Sta-Rite System:3 filter tanks.
• Creates a watertight tank seal — helps prevent leaks between filter tank sections.
• Fits multiple System:3 filter types — compatible with select cartridge, D.E., and sand filter models.
• Replacement for part 24850-0008 — direct replacement reference for compatible Sta-Rite / Pentair filter diagrams.
• O-485 cross-reference — commonly cross-referenced with O-485 replacement tank O-ring.
• Large tank seal design — supports proper pressure sealing during filter operation.
• Flexible rubber construction — compresses to help maintain a tight seal when properly lubricated and installed.
• Service-friendly replacement part — commonly replaced during filter cleaning, tank service, or leak repair.
• Helps maintain filtration performance — proper sealing supports stable pressure and leak-free operation.
• Cost-effective repair part — replaces the O-ring without replacing the complete filter tank.

Benefits

The Sta-Rite 24850-0008 tank O-ring helps restore a secure seal on compatible System:3 filters. A worn or damaged tank O-ring can cause leaks, pressure loss, air intrusion, or difficulty keeping the filter clamped correctly.

Replacing the O-ring during filter service can help prevent water leaks and protect the filter from improper sealing. For best results, the O-ring should be inspected whenever the filter tank is opened and replaced if it shows signs of wear, cracking, flattening, swelling, or damage.

For pool professionals, this is a practical replacement part to keep on hand for System:3 filter service calls.

Specifications

Included Components

• 1 × Sta-Rite / Pentair 24850-0008 21" System:3 tank O-ring

Filter tank, clamp assembly, clamp bolt, cartridges, D.E. grids, filter sand, pressure gauge, air relief assembly, drain plugs, O-ring lubricant, and installation labor are sold separately unless specifically included by the supplier.

Compatibility Notes

This O-ring is designed for select Sta-Rite System:3 filters with 21" tanks.

Common compatibility references include:

• Sta-Rite System:3 Modular Media cartridge filters
• Sta-Rite System:3 SM Series filters
• Sta-Rite System:3 SD Series D.E. filters
• Sta-Rite System:3 SMD Series D.E. filters
• Sta-Rite System:3 sand filters
• S7M120
• S7M400
• S8M150
• S8M500
• S7D75
• S8D110
• S7MD60
• S7MD72
• S7S50

Always confirm the filter model number, tank size, part diagram, and existing O-ring before ordering. This O-ring is for compatible 21" System:3 tanks and is not universal for all Sta-Rite filters.

Installation Notes

Turn off the pump and relieve all pressure from the filter before opening the tank. Remove the old O-ring and clean the sealing groove and mating surfaces thoroughly.

Inspect the new O-ring for damage before installation. Apply a pool-safe silicone-based O-ring lubricant if recommended by the filter manufacturer. Seat the O-ring evenly in the groove without twisting, stretching, or pinching it.

Reassemble the tank carefully and secure the clamp according to the manufacturer’s instructions. After startup, bleed air from the filter and inspect the tank seam for leaks.

Never open or loosen a filter tank while it is pressurized.

Customer-Facing Q&A

Q: What is the Sta-Rite 24850-0008?
A: It is a 21" tank O-ring for compatible Sta-Rite System:3 pool and spa filters.

Q: What is the SKU?
A: The SKU is 24850-0008.

Q: What is the UPC / barcode?
A: The UPC / barcode is 788379828738.

Q: What does this O-ring do?
A: It seals the filter tank sections to help prevent water leaks and maintain proper filter pressure.

Q: What filter series does it fit?
A: It fits select Sta-Rite System:3 filters with 21" tanks.

Q: What are common compatible models?
A: Common references include S7M120, S7M400, S8M150, S8M500, S7D75, S8D110, S7MD60, S7MD72, and S7S50.

Q: Is this the same as O-485?
A: Yes. O-485 is a common cross-reference for this 21" System:3 tank O-ring.

Q: Does this include the clamp?
A: No. This listing is for the O-ring only.

Q: Should I lubricate the O-ring before installation?
A: Use a pool-safe silicone-based O-ring lubricant if recommended by the filter manufacturer. Do not use petroleum-based lubricants.

Q: Should this be professionally installed?
A: Professional installation is recommended because pool filters operate under pressure and must be reassembled correctly for safe operation.