Astralpool Pump Check Valve Assembly
Astralpool Pump Check Valve Assembly is temporarily out of stock and will ship as soon as it's available.
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Astralpool Pump Check Valve Assembly
Astralpool Pump Check Valve Assembly is temporarily out of stock and will ship as soon as it's available.
Astralpool Pump Check Valve Assembly 598770
Genuine Astralpool / Hurlcon in-pump check valve, part number 598770, for the E, CX, TX and CTX pumps. Suits both 40mm and 50mm unions. It prevents impeller "spin-off" — water rushing backwards through the pump when it switches off — and helps the pump hold prime between cycles.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
Important Notes Before Ordering
- Supplied only in the current style shown in the first image. The older black-fitting style (second image) is discontinued; the new version suits most applications.
- In some 40mm-tail installations the flap will not fully open, and there is no way to know until you try. If it does not open fully, fit a separate check valve above the pump instead.
- Where possible we recommend a good-quality check valve fitted to the pump outlet.
A Note on Check Valves and Safety Systems
Astralpool cautions that a check valve can interfere with the operation of certain Suction Vacuum Release Systems (SVRS). If your pool has an SVRS fitted, review its manual before installing an in-line check valve. On pumps installed below water level, isolation (check) valves on both suction and return lines are what let you service the pump without draining the lines.
Related Parts
- 40065 — basket (buy here)
- 70006 — lid o-ring (buy here)
- 75508 / PS3868 — mechanical seal (buy here)
- Impeller — sized to your model, see the CTX impeller range
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers or diagrams? See the manufacturer catalogues: Astralpool Catalogue 2026 | Zodiac Catalogue 2026
Common search terms: Astralpool 598770, CTX check valve, in-pump check valve, Astral Hurlcon non-return valve, pump anti-spin-off valve, 40mm 50mm check valve.
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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598770