Astralpool Cell Nut Cup / Terminal Cover 70391 - E-Series, VX, Viron, eQuilibrium & Halo - Genuine Chlorinator Spare Part
Astralpool Cell Nut Cup / Terminal Cover 70391 - E-Series, VX, Viron, eQuilibrium & Halo - Genuine Chlorinator Spare Part is temporarily out of stock and will ship as soon as it's available.
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 Cell Nut Cup / Terminal Cover 70391 - E-Series, VX, Viro...
Astralpool Cell Nut Cup / Terminal Cover 70391 - E-Series, VX, Viron, eQuilibrium & Halo - Genuine Chlorinator Spare Part is temporarily out of stock and will ship as soon as it's available.
Astralpool Cell Nut Cup / Terminal Cover 70391 - E-Series, VX, Viron, eQuilibrium & Halo
Genuine Astralpool 70391 - the cell nut cup, also called the terminal cover or cell end cap. It fits over the top of the cell and shields the electrode cable connection from UV, rain and debris.
- We keep these physically in stock for fast shipping or local pick-up, unlike most drop-shipping websites.
- Shipped from VIC, NSW, WA, QLD
Cell nut cup or cell nut? They are different parts
These two are frequently confused because they sit together on the same cell and are often sold as a pair:
- 70391 - cell nut cup / terminal cover: this product. The cup that covers the terminal connection.
- 70390 - cell nut: the threaded locking nut that clamps the electrode into the clear housing. Buy the cell nut here.
If the electrode is loose in the housing, you need the nut. If the terminal connection is exposed to weather, you need this cup.
Suits the following chlorinators
- Astralpool E-Series - E25, E35
- Astralpool / Hurlcon VX Series - VX6, VX7, VX9, VX11 and T variants
- Astralpool Viron - V18, V25, V35, V45
- Astralpool Viron eQuilibrium - EQ18, EQ25, EQ35, EQ45
- Astralpool Halo - Halo 18, Halo 25, Halo 35, Halo 45
- Filtrite branded chlorinators using the same cell housing
The cell hardware is shared across these ranges. Note that the electrodes are not - VX and E-Series use the 219xx cell range while Viron, eQuilibrium and Halo use the 129xx range.
When to replace it
- Cup is cracked, split or has gone brittle with UV exposure
- Cup is missing and the terminal connection is open to the weather
- Corrosion is appearing at the cell terminal
- Cup no longer clips or seats over the nut
A missing terminal cover lets water sit on the connection. Corrosion there causes low output and intermittent faults that look exactly like a worn electrode, so it is worth replacing a broken cup rather than running without one.
Related Parts
- 70390 - cell nut (buy here)
- 70570 - external clear cell body, the V4 housing (buy here)
- 78104 - cell body o-ring. Replace whenever the cell is opened (buy here)
See the full range of genuine Astralpool and Zodiac chlorinator cells and electrodes.
Before ordering
Chlorinator cell hardware changed across production periods, and older VX housings use different components to the current V4 housing. Confirm this part is correct for your equipment before ordering. Use the catalogue below, seek professional assistance, or contact us with photos of your existing part, model details, serial numbers and any labels.
As with all products, this must be diagnosed and fitted by a qualified and experienced person.
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
Common search terms: Astralpool 70391, Astral 70391, cell nut cup, chlorinator terminal cover, cell end cap, VX cell cap, Viron cell terminal cover, EQ cell cap, Halo cell cap, E-Series cell cap, Hurlcon cell cap, WWDG SpaPro.
To the layperson, plumbing sizes and their names can be confusing due to the nominal sizes and naming conventions used.
This is not something we made up. Plumbers and manufacturers have used nominal (meaning ‘by name only’) sizing for decades.
Simply put, in plumbing, named sizes are often not the actual measurements of the pipe, fitting, or part. A PVC pipe called “50mm” or “2"” does not measure 50 mm anywhere. Instead, it follows nominal sizing, an internationally-standardised naming system.
Almost all fittings we use in the pool & spa industry use “pressure PVC” pipe & fittings. Do not confuse with “DWV” or other pipe & fittings and their names and sizes.
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 |
To reiterate, these are nominal sizes and are designed to fit matching fittings — not to measure 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 and other plumbing areas 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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