Astralpool Diffuser Small - BX / CTX 180-400 / E-Series 40071A

Astralpool Diffuser Small - BX / CTX 180-400 / E-Series 40071A

This is the genuine Astralpool small diffuser, part number 40071A (supplied as SP40071A). The diffuser sits over the impeller and directs flow into the volute. Astralpool fits two sizes across this pump family, and they are not interchangeable — this is the small one, for the CTX 180, 280, 360 and 400, the Viron XT P320, the BX / E-series and the P280 / P300 pumps.

• Physically Stocked, unlike most "drop-shipping" websites.
• Shipped from VIC, NSW, WA, QLD

Large or Small? Get This Right First

The single most common diffuser mistake is ordering the wrong size, because both look similar in a photo. Match your pump to the correct part:

Note the Viron split: the XT P320 uses this small diffuser (40071A), while the XT P520 uses the large 40071B. As with the impellers, the two Viron XT pumps do not share this part.

Confirmed Compatibility

Astralpool lists 40071A as the small diffuser for:

• CTX 180, 280, 360 and 400
• Viron XT P320 and P320 C XT
• BX and E-series pumps (small)
• P280 / P300 family

If your pump is a CTX 500 or 610, or a Viron XT P520, you need the large diffuser 40071B instead.

Related Parts

• 40165 — diffuser retaining screws (x2)
• 78104 — diffuser o-ring (buy here)
• 40060F — impeller, CTX 360 / P280 / P320 eVo (buy here)
• 40060X — impeller, Viron XT P320 (buy here)
• 75508 / PS3868 — mechanical seal, BX / TX / CX / E / CTX (buy here)
• 40065 — basket (buy here)
• 40089 — lid complete with o-ring (buy here)

When to Replace

Replace the diffuser if it is cracked, if the sealing face against the seal plate is distorted, or if the vane passages are damaged. A cracked or poorly seated diffuser lets water bypass the impeller, which shows up as reduced flow and pressure even with a good impeller fitted. The diffuser o-ring should be replaced at the same time.

Frequently Asked Questions

How do I know if I need the small or large diffuser?
Match your pump model. CTX 180-400, the Viron XT P320, and smaller BX / E-series pumps use this small 40071A. CTX 500, CTX 610 and the Viron XT P520 use the large 40071B.

Does the Viron XT P520 use this diffuser?
No. The XT P520 uses the large 40071B. Only the smaller XT P320 uses this small 40071A.

Should I replace the o-ring too?
Yes. The diffuser o-ring, 78104, should go in with a new diffuser.

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 40071A, SP40071A, CTX diffuser small, Viron XT P320 diffuser, BX diffuser, E-series diffuser, Astral Hurlcon diffuser small.