Astralpool / Zodiac Cap ZX Filter Drainage Blank 78218
Astralpool / Zodiac Cap ZX Filter Drainage Blank 78218 is temporarily out of stock and will ship as soon as it's available.
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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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Astralpool / Zodiac Cap ZX Filter Drainage Blank 78218
Astralpool / Zodiac Cap ZX Filter Drainage Blank 78218 is temporarily out of stock and will ship as soon as it's available.
Astralpool ZX / Zodiac ZXC Filter Drain Blanking Cap (with Drain) — 78218
Genuine Astralpool blanking cap with drain for the ZX-family cartridge filter, part number 78218. It seals the 50mm port on the base of the ZX tank and carries a small screw drain for winterising or emptying the filter. Supplied on its own.
- 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.
Cap With Drain, Or Plain Blank?
Astralpool makes two caps for this 50mm port — order the right one:
- 78218 — blanking cap with a screw drain (this item).
- 78214 — plain 50mm blanking cap, no drain. Get the plain version here.
Fits Across The ZX Range
- Astralpool ZX / Hurlcon ZX: ZX50 to ZX310
- Zodiac ZXC: ZXC50 to ZXC310
- Zodiac ZCF / Titan ZCF: ZCF75 to ZCF200
- Astral SMART / Filtrite CF / Aquatight: ZX-style cartridge filters
Will Not Fit
- Astralpool XC — a separate, unrelated filter series. Contact us with your model and a photo.
Part Numbers & Search References
78218 · SP78218 · Cap ZX Filter Drainage Blank · ZX drain cap · 50mm blanking cap with drain · Zodiac ZXC filter drain plug · Hurlcon ZX drain blank.
Frequently Asked Questions
Does this cap have a drain?
Yes. Part 78218 is the blanking cap with a screw drain. The plain blank with no drain is part 78214.
Which port does it fit?
The 50mm port on the base of the ZX tank.
My filter is a Zodiac ZXC. Is this the right cap?
Yes. The Zodiac ZXC is the same filter as the Astralpool ZX, just Zodiac-badged, so this cap fits.
My filter is an Astralpool XC. Is this the right cap?
No. The XC is a separate, unrelated filter series. Contact us with your model and a photo and we will match 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
As with all products, these must be diagnosed and fitted by a qualified and experienced person. This is a special-order item.
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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