Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII
Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII is temporarily out of stock and will ship as soon as it's available.
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Don't Guess - Ask Us!
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Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII
Astralpool ZX / Zodiac ZCF Cartrildge Filter O-Ring Seal - MKII is temporarily out of stock and will ship as soon as it's available.
Astralpool ZX / Zodiac ZXC Cartridge Filter Lid O-Ring (Tank Seal) — 78110 / 78105
This is the genuine Astralpool lid O-ring — also called the tank O-ring or lid seal — for the ZX-family cartridge filter, current part number 78110 (old number 78105). It seals the filter lid to the tank body. One O-ring fits the whole ZX range. Replace it if the filter lid is leaking, weeping, drawing air or hard to tighten, or if the old seal is flattened, cracked, stretched or perished.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
This is the same filter sold under several brands — Astralpool ZX, Hurlcon ZX, Zodiac ZXC, Zodiac ZCF / Titan ZCF, Astral SMART, Filtrite CF and Aquatight. The Zodiac ZXC is simply the Zodiac-badged Astralpool ZX.
Identification
- Genuine Astralpool part
- Current part number: 78110
- Old / superseded number: 78105
- Approximate size: 280mm outside diameter
- Cross-section: approximately 5mm
- Diagram reference: Item 4 on many ZX diagrams, Item 7 on some ZCF diagrams
Fits Across The ZX Range
One tank O-ring fits every ZX-family filter, from the ZX50 to the ZX310:
- Astralpool ZX / Hurlcon ZX: ZX50 to ZX310
- Zodiac ZXC: ZXC50 to ZXC310
- Zodiac ZCF / Titan ZCF: ZCF75 to ZCF200
- Astral SMART: SMART 350 / 450 / 550
- Filtrite CF / Aquatight: ZX-style cartridge filters
- Astral IX / IX50 in-line leaf canister (same tank O-ring)
Installation Note
Clean the lid and tank sealing groove before fitting the new O-ring — dirt, grit, old lubricant and calcium build-up will stop the lid sealing correctly. Apply a light smear of silicone-based O-ring lubricant before refitting. Do not use petroleum grease, as it swells and damages rubber seals. It is good practice to fit a new O-ring whenever you fit a new lid, since the old seal has taken a set to the old lid's sealing face.
When To Replace This O-Ring
- Water leaks or weeps 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 off for cartridge cleaning and the seal no longer sits properly
Need The Complete Lid Assembly?
If the lid, locking ring or handles are also damaged, you may need the complete lid assembly rather than just the O-ring. Click here for the Astralpool ZX / ZXC cartridge filter lid assembly — SP7820502.
Will Not Fit
- Hurlcon QX — a different filter with a 222mm lid.
- Astralpool XC — a separate, unrelated filter series. Contact us with your model and a photo.
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 · Zodiac ZXC lid seal · Astralpool ZX lid seal · Hurlcon ZX lid seal · 280mm cartridge filter O-ring.
Frequently Asked Questions
Does one O-ring fit all ZX filters?
Yes. The same tank O-ring, part 78110, fits every ZX-family filter from the ZX50 to the ZX310.
My filter is a Zodiac ZXC. Is this the right O-ring?
Yes. The Zodiac ZXC is the same filter as the Astralpool ZX, just Zodiac-badged, so this O-ring fits.
My filter is an Astralpool XC. Is this the right O-ring?
No. The XC is a separate, unrelated filter series and does not use the ZX tank O-ring. Contact us with your model and a photo and we will match the correct part.
Do I need a new O-ring if I am fitting a new lid?
Strongly recommended. The old O-ring has conformed to the old lid's sealing face and is the usual reason a brand new lid still weeps.
What lubricant should I use?
A silicone-based O-ring lubricant only. Never use petroleum grease, which swells and destroys the rubber.
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
As with all products, these must be diagnosed and fitted by a qualified and experienced person.
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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