Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII
Don't Guess - Ask Us!
Don't Guess - Ask Us!
Not sure if it’s the right part? Send us a message and a photo of what you’re replacing, or what you need, and we’ll help make sure you get the right part the first time.
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Delivery and Shipping Info*
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Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII
Genuine AstralPool / Hurlcon ZX / Zodiac ZCF Cartridge Filter Lid O-Ring for AstralPool ZX, Hurlcon ZX, Zodiac ZCF, Astral SMART and compatible cartridge filter tanks.
This is the main filter lid O-ring, also called the tank O-ring or lid seal. It seals the filter lid to the tank body. Replace this O-ring if the filter lid is leaking, weeping water, drawing air, difficult to tighten, or if the existing seal is flattened, cracked, stretched or perished.
- Genuine AstralPool / Fluidra part
- Current part number: 78110
- Old / superseded part number: 78105
- Approximate size: 280mm outside diameter
- Cross-section: approximately 5mm
- Common diagram reference: Item 4 on many ZX diagrams, Item 7 on some ZCF diagrams
Compatible Models
AstralPool / Hurlcon ZX cartridge filters:
- ZX50 / ZX 50
- ZX75 / ZX 75
- ZX100 / ZX 100
- ZX150 / ZX 150
- ZX200 / ZX 200
- ZX250 / ZX 250
- ZX310 / ZX 310
Zodiac ZCF / Titan ZCF cartridge filters:
- ZCF75 / ZCF 75
- ZCF100 / ZCF 100
- ZCF150 / ZCF 150
- ZCF200 / ZCF 200
Astral Leisure Pools SMART cartridge filters:
- SMART 350 / Smart 350
- SMART 450 / Smart 450
- SMART 550 / Smart 550
Also commonly cross-referenced with:
- Astral IX / IX50 in-line leaf canister tank O-ring
- Some Filtrite CF cartridge filter applications where the filter uses the Astral / Hurlcon ZX-style lid and tank assembly
Part Numbers & Search References
- 78110
- 78105
- O Ring Lid ZX Filter MK2
- ZX Cartridge Filter Lid O-Ring
- ZX Cartridge Filter Tank O-Ring
- ZCF Cartridge Filter Lid O-Ring
- ZCF Cartridge Filter Tank O-Ring
- AstralPool ZX lid seal
- Hurlcon ZX lid seal
- Zodiac ZCF lid seal
When To Replace This O-Ring
- Water leaks from around the filter lid
- The lid is hard to tighten or does not seat smoothly
- The pump draws air through the filter lid
- The old O-ring is flat, brittle, cracked, swollen or stretched
- The lid has been removed for cartridge cleaning and the seal no longer sits properly
Installation Note
Clean the lid and tank sealing groove before fitting the new O-ring. Dirt, grit, old lubricant and calcium build-up can stop the lid from sealing correctly. Apply a light smear of silicone-based O-ring lubricant before refitting. Do not use petroleum grease, as it can damage rubber seals.
Need The Complete Lid Assembly?
If your lid, lock ring or handles are damaged, you may need the complete lid assembly instead of just the O-ring. Click here for the AstralPool ZX / SMART cartridge filter lid assembly.
Not sure if this is the right seal? Check your filter model label or measure your existing O-ring. You can also send us a photo of the filter label, lid and old O-ring and we can help confirm the correct part.
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers, diagrams, or more product information? See the manufacturer catalogues: AstralPool Catalogue 2026 | Zodiac Catalogue 2026
In plumbing, named sizes are not the actual measurements. A pipe called “50mm” or “2"” does not measure 50 mm across. Instead, it follows nominal sizing, an internationally-standardised naming system.
Use the Outside Diameter (OD) to check your pipe against fittings. Below is a quick reference for common spa & pool pipe sizes:
| Imperial Name | Metric Name | Pipe Diameter (OD) |
|---|---|---|
| 1/2" | 15mm | ~21.2–21.5 mm |
| 3/4" | 20mm | ~26.6–26.9 mm |
| 1" | 25 mm | ~33.4–33.7 mm |
| 1.5" | 40 mm | ~48.1–48.4 mm |
| 2" | 50 mm | ~60.2–60.8 mm |
| 2.5" | 65 mm | ~75.2–75.5 mm |
These are nominal sizes and are designed to fit matching fittings — not to measure exactly what their name suggests. These are based on PVC Pressure Pipe AS/NZ 1477 Dimensions1.
- º Internal diameters vary slightly by manufacturer and class.
- 1 Not all pool/spa fittings match these dimensions exactly. Some do not follow Australian or international standards. Chinese spas may use proprietary fittings.
Understanding Plumbing Sizes & Nominal Measurements
Plumbing sizes can be confusing. PVC and many other pipe systems use nominal sizes—the size is a name, not the exact measured dimension. This convention is used across most pool and spa systems so that pipes and fittings remain compatible.
Why pipe sizes don’t match the measurements
The Nominal Pipe Size (NPS) system standardises pipe dimensions so that pipes, fittings, valves, and accessories interoperate. Plumbers work with these nominal names every day, but DIYers can be tripped up if they try to match by a tape-measure alone.
How to Measure Pipe Correctly
-
Pipe size is identified by:
- The pipe’s Outside Diameter (OD).
- The fitting’s Inside Diameter (ID) (socket opening).
- Pipe Class / Schedule (e.g., Class 9, 12, 18 or Sch 40) relates to wall thickness and therefore the Internal Diameter (ID) and pressure rating.
- The outside diameter of a fitting is not useful (wall thickness varies by manufacturer).
Hose & Tube Dimensions
Common flexible hose sizes used in pool/spa systems (approximate IDs).
| Imperial Name | Metric Name | Inside Diameter (ID) |
|---|---|---|
| 3/8" | 9–10 mm | ~9 mm |
| 3/4" | 19 mm | ~19 mm |
BSP – British Standard Pipe Thread Sizes
BSP thread names are also nominal. The thread OD will not equal the nominal name.
| BSP Thread Size Naming | Outside Diameter (mm / inch) | TPI |
|---|---|---|
| 1/16" BSP | 7.7 mm / 0.304" | 28 |
| 1/8" BSP | 9.7 mm / 0.383" | 28 |
| 1/4" BSP | 13.16 mm / 0.518" | 19 |
| 3/8" BSP | 16.66 mm / 0.656" | 19 |
| 1/2" BSP / 15 mm | 20.99 mm / 0.825" | 14 |
| 5/8" BSP | 22.99 mm / 0.902" | 14 |
| 3/4" BSP / 20 mm | 26.44 mm / 1.041" | 14 |
| 7/8" BSP | 30.20 mm / 1.189" | 14 |
| 1" BSP / 25 mm | 33.25 mm / 1.309" | 11 |
| 1-1/4" BSP | 41.91 mm / 1.650" | 11 |
| 1-1/2" BSP / 40 mm | 47.80 mm / 1.882" | 11 |
| 2" BSP / 50 mm | 59.61 mm / 2.347" | 11 |
| 2-1/4" BSP | 65.71 mm / 2.587" | 11 |
| 2-1/2" BSP | 75.18 mm / 2.960" | 11 |
| 3" BSP | 87.88 mm / 3.460" | 11 |
| 4" BSP | 113.03 mm / 4.450" | 11 |
| 5" BSP | 138.43 mm / 5.450" | 11 |
| 6" BSP | 163.83 mm / 6.450" | 11 |
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