Astralpool Diffuser Large - CTX 500 / 610, Viron XT P520, BX 40071B

Astralpool Diffuser Large - CTX 500 / 610, Viron XT P520, BX 40071B

This is the genuine Astralpool large diffuser, part number 40071B. 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 large one, for the higher-flow pumps: CTX 500 and CTX 610, the Viron XT P520, and the larger BX 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 P520 uses this large diffuser (40071B), while the XT P320 uses the small 40071A. As with the impellers, the two Viron XT pumps do not share this part.

Confirmed Compatibility

Astralpool lists 40071B as the large diffuser for:

• CTX 500 and CTX 610
• Viron XT P520 and P520 C XT
• Larger BX pumps

If your pump is a CTX 180 through 400, or a Viron XT P320, you need the small diffuser 40071A instead.

Related Parts

• 40165 — diffuser retaining screws (x2)
• 78104 — diffuser o-ring (buy here)
• 40060V — impeller, CTX 500 (buy here)
• 40060Z — impeller, Viron XT P520 (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 large or small diffuser?
Match your pump model. CTX 500, CTX 610, Viron XT P520 and larger BX pumps use this large 40071B. CTX 180-400 and the Viron XT P320 use the small 40071A.

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

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 40071B, CTX 500 diffuser, CTX 610 diffuser, Viron XT P520 diffuser, BX large diffuser, Astral Hurlcon diffuser large.