Astralpool Component Bag - 40mm & 50mm Unions, Tails & Check Valve 78303
Astralpool Component Bag - 40mm & 50mm Unions, Tails & Check Valve 78303 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 Component Bag - 40mm & 50mm Unions, Tails & Chec...
Astralpool Component Bag - 40mm & 50mm Unions, Tails & Check Valve 78303 is temporarily out of stock and will ship as soon as it's available.
Astralpool Component Bag - 40mm & 50mm Unions, Tails & Check Valve 78303
Genuine Astralpool plumbing component bag, part number 78303. This is the loose hardware pack supplied with the pump — the union nuts, barrel tails and the in-pump check valve that connect the wet end to your suction and return lines. If the bag was lost during the original install, or the unions have been cross-threaded or cracked, this restores the set in one purchase.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
What Is In The Bag
- Union nuts and barrel tails to suit both 40mm and 50mm plumbing
- Union tail o-rings
- In-pump check valve (598770) — the loose non-return flap that ships inside the pump basket
Why Both Sizes Are Supplied
Astralpool ships the pump able to plumb either way. Most Australian domestic pools run 50mm on the CTX and E-Series; older CX and TX installs are commonly 40mm. The bag covers both so the installer can match whatever is already in the ground without a second trip.
About The Check Valve
The check valve is supplied loose in the basket, not fitted. It stops water rushing backwards through the pump when it shuts down. Astralpool specifies it for spas on cartridge filters, any time multiple pumps share one suction or return line, and any install where back-flow can occur. It does slightly reduce flow, which is why it is supplied loose rather than pre-fitted.
Buying The Pieces Separately
If you only need one item rather than the full bag:
- 950920 — 50mm union tail on its own (buy here)
- 78104 — 65mm union tail o-ring (buy here)
- 598770 — check valve assembly on its own (buy here)
Fits These Pumps
- Astralpool CTX — CTX 180, 280, 360, 400, 500 (including MkII)
- Astralpool E-Series — E 140, E 170, E 230
- Hurlcon & Astralpool CX and TX ranges
- Astralpool Viron XT — P320 XT, P520 XT
Common search terms: Astralpool 78303, component bag CTX, 50mm heater tail bag, Astral pump union kit, Hurlcon union nut and tail set, CTX check valve bag.
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers or diagrams? See the manufacturer catalogue: Astralpool Catalogue 2026 | Zodiac Catalogue 2026
Before ordering: confirm this part is correct for your pump. Use the catalogue above, 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. This is a special-order item.
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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