Astralpool Volute (Wet End) - CTX / E-Series MkII, Nov 2020 SP40031
Astralpool Volute (Wet End) - CTX / E-Series MkII, Nov 2020 SP40031 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 Volute (Wet End) - CTX / E-Series MkII, Nov 2020 SP40031
Astralpool Volute (Wet End) - CTX / E-Series MkII, Nov 2020 SP40031 is temporarily out of stock and will ship as soon as it's available.
Astralpool Volute (Wet End) - CTX / Viron / E-Series MkII, Nov 2020 SP40031
This is the genuine Astralpool MkII volute, part number SP40031 (catalogue 40031). The volute is the main pump body (wet end) that houses the impeller, diffuser and basket. This is the current-style wet end introduced from November 2020, used across the CTX MkII, Viron and E-Series MkII pumps.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
Three Generations — Order the Right One
Astralpool changed the CTX wet end twice. The volute and its matching seal plate must come from the same generation as your pump, or they will not bolt up and seal correctly. Identify your pump's era before ordering:
| Generation | Volute (wet end) | Seal plate |
|---|---|---|
| Series 1 — old style, pre-Aug 2014 | 4007502 | 4009002 |
| Series 2 — Aug 2014 to 2018 | 40097 | 40098 |
| MkII — Nov 2020 onwards | SP40031 — this product | SP40030 |
If you are not sure which generation your pump is, send us a photo of the pump and its data plate and we will identify it. This is an expensive part to order wrongly.
Fits These MkII Pumps
The MkII wet end and its matching seal plate (SP40030) are shared across a wide range of current-generation pumps:
- CTX MkII — CTX 280, CTX 360C, CTX 400, CTX 500
- E-Series MkII — 140C, 170C, 230C
- Viron P320 & P520 XT (Nov 2020 to June 2021 build)
- AstralPool XP pump range
What the Volute Is
The volute is the moulded pump body that the motor bolts onto. It holds the basket, the diffuser and the impeller, and forms the pressure chamber that converts the impeller's spin into water flow. It is replaced when the body is cracked, when a union or port thread has failed, or when the internal sealing faces are damaged beyond what a new seal plate and o-rings will fix.
Related MkII Parts
- SP40030 — seal plate, MkII Nov 2020 (buy here)
- 70022 — seal plate o-ring
- 75509 — mechanical seal, current pumps (buy here)
- 78772 — seal plate to wet end bolts (x6)
- 40065 — basket (buy here)
- 40089 — lid complete with o-ring (buy here)
- Impeller — sized to your model, see the CTX or Viron XT impeller ranges
Frequently Asked Questions
How do I know if my pump is MkII?
MkII wet ends were fitted from November 2020. They cover the CTX MkII, E-Series MkII, AstralPool XP range, and the Viron P320/P520 XT of the Nov 2020 to June 2021 build. If unsure, send us a photo of the data plate.
Can I fit a Series 1 or Series 2 volute instead?
The generations are not cross-compatible as a mix. The volute, seal plate and their o-rings changed together. Match the whole wet end to one generation.
Does this cover the AstralPool XP pumps?
Yes. The MkII wet end and SP40030 seal plate are listed for the AstralPool XP range alongside the CTX MkII and Viron XT pumps.
Is this a genuine Astralpool part?
Yes. We are an authorised Astralpool and Fluidra dealer and warranty agent.
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers or diagrams? See the manufacturer catalogue: Astralpool 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.
Common search terms: Astralpool SP40031, 40031 volute, CTX MkII wet end, Viron XT volute Nov 2020, AstralPool XP pump body, E-Series MkII volute.
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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SP40031