Astralpool Multiport Valve Sight Glass 40mm & 50mm - Post Sept 2009 - 75906
Astralpool Multiport Valve Sight Glass 40mm & 50mm - Post Sept 2009 - 75906 is temporarily out of stock and will ship as soon as it's available.
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Warranty Information
Warranty Information
Astralpool Multiport Valve Sight Glass 40mm & 50mm - Post Sept ...
Astralpool Multiport Valve Sight Glass 40mm & 50mm - Post Sept 2009 - 75906 is temporarily out of stock and will ship as soon as it's available.
Astralpool Multiport Valve Sight Glass 40mm & 50mm - Post Sept 2009 - 75906
- We keep these physically in stock for fast shipping or local pick-up, unlike most drop-shipping websites.
- Shipped from VIC, NSW, WA, QLD
75906 is the genuine Astralpool sight glass for 40mm and 50mm multiport valves made from September 2009 onwards. It is the clear window on the waste side of the valve, so you can watch the water during backwash and rinse and stop once it runs clear. Astralpool lists it as the Sightglass - 40mm/50mm - MPV on its Multiport Valve - Sep 09 - Current parts list, and as the Observe Lid on the diagrams for the 50mm 76053 valve (CA300, CA340, CA400) and the 40mm 76036 valve (ECA550, ECA650).
This listing is the sight glass only. Its gasket (the sight glass o-ring) is 75917, sold separately. Fit a new gasket whenever the glass comes out, or order both together as the Sight Glass with Seal.
The September 2009 Valve Rule (rev. MPV-SG-1.0)
This sight glass suits the valve, not the filter tank. Check the valve before ordering:
- Check the valve date. Astralpool lists 75906 for its 40mm and 50mm multiport valves made from September 2009 onwards. It is No. 17 on the Multiport Valve - Sep 09 - Current parts list.
- Read the filter label. CA300, CA340 and CA400 filters use the 50mm valve 76053. ECA550 and ECA650 filters use the 40mm valve 76036. The CA280 uses the 40mm CA valve 76044. All of these take 75906.
- Valve already apart? Check the spider gasket. On a 40mm valve made from September 2009, the spider gasket is 128mm across with 4 spokes (75916).
- Zodiac top mount valve? The Zodiac valves on APV fibreglass filters take a different sight glass: W89280104 on the 50mm valve, or the 40mm union with sight glass W89280101 on the APV650.
- Older valve, a Cantabric filter, or not sure? Send us a photo of the valve before ordering. Hurlcon valves made before September 2007 take a different sight glass, 75073.
Worked Example
Say a CA340 is due for a backwash, but the sight glass has gone cloudy and you cannot tell when the water runs clear. The tank label reads CA340, which Astralpool supplies with the 50mm valve 76053, and the 76053 parts list includes this sight glass (No. 18) and its gasket 75917 (No. 19). With the pump off and the pressure released, unscrew the old glass, fit a new gasket and screw in the new glass. If instead you can see water moving in the sight glass while the valve is set to Filter, a new glass will not fix it. That water is getting past the spider gasket, 75929 on the 50mm valve.
Which Part Do I Need?
| What you see | What to order |
|---|---|
| Sight glass cracked, crazed, or too cloudy to see the backwash water | This sight glass, 75906, with a new gasket 75917, or both together as the Sight Glass with Seal |
| Water weeping around the sight glass, glass clear and uncracked | Gasket 75917 |
| Water moving in the sight glass, or running to waste, while the valve is set to Filter | Not the sight glass. Usually the spider gasket: 40mm 75916 or 50mm 75929 |
| Zodiac 50mm top mount valve (APV700, APV800, APV900 fibreglass filters) | Zodiac sight glass with o-ring W89280104 |
| APV650 fibreglass filter | 40mm union with sight glass W89280101 |
Fitment
An older filter may still carry an earlier valve, so check the valve as well as the filter model. Astralpool's 2026 catalogue lists 75906 on these valves:
| Valve | Port size | Fitted to | Catalogue reference |
|---|---|---|---|
| 76053 | 50mm | Astralpool CA300, CA340, CA400 | 2026 catalogue, page 82, No. 18 |
| 76036 | 40mm | Astralpool ECA550, ECA650 | 2026 catalogue, page 83, No. 20 |
| 76044 | 40mm | Astralpool CA280 | 2026 catalogue, pages 15 and 81, No. 17 |
Australian parts suppliers also list 75906 for these valves made from September 2009:
- Astral EC 40mm valve 76037, as fitted to EC550 and EC650 filters
- Hurlcon and Astralpool RX, E and FG series valves (40mm 76032, 50mm 76033)
Astralpool's 2026 catalogue does not list these valves in its current filter spare parts pages, so check the valve date or send us a photo before ordering.
What This Sight Glass Does Not Fit
- Zodiac top mount valves, as fitted to APV fibreglass filters. Astralpool's catalogue lists W89280104 for the 50mm valve on the APV700, APV800 and APV900, and the 40mm union with sight glass W89280101 for the APV650.
- Hurlcon valves made before September 2007. These take a different sight glass, 75073.
Not confirmed: Astralpool and Hurlcon valves made between September 2007 and September 2009, and Cantabric filter valves. Send us a photo of the valve and we will confirm what fits.
When to Replace
- The glass is cracked or crazed, or damaged at the thread.
- It has clouded or stained so you can no longer see when the backwash water runs clear.
- It still weeps after a new gasket has been fitted.
Fit a new gasket, 75917, whenever the sight glass is removed.
Fitting Notes
- Turn the pump off and release the pressure from the filter before removing the sight glass.
- Unscrew the old sight glass from the valve and remove the old gasket.
- Fit a new gasket, 75917, and screw the new sight glass in firmly by hand. Do not over-tighten.
- Restart the pump and check around the sight glass for leaks during the next backwash.
Specifications
- Part number: 75906
- Astralpool description: Sightglass - 40mm/50mm - MPV
- Also listed as: Observe Lid
- Diagram reference: No. 17 on the Multiport Valve - Sep 09 - Current list, No. 18 on the 50mm 76053 diagram, No. 20 on the 40mm 76036 diagram
- Quantity per valve: 1
- Port sizes: 40mm and 50mm valves
- Valve generation: September 2009 onwards
- Gasket: 75917, sold separately
- Barcode: 9343609028572
Related Multiport Valve Parts
- Sight Glass O-Ring, MPV 40mm & 50mm - 75917
- Sight Glass with Seal - 75906 + 75917
- Spider Gasket 40mm MPV, 128mm 4-spoke - 75916
- Spider Gasket 50mm MPV - 75929
- Spring, MPV - 75912
- Shaft O-Ring, MPV 40mm & 50mm - 75905
- Handle, MPV 40mm & 50mm - 75903
- Plug, MPV 40mm & 50mm - 75908
- Multiport Valve 40mm, ECA550 / ECA650 - 76036
- Multiport Valve 50mm, CA300 / CA340 / CA400 - 76053
Frequently Asked Questions
Does 75906 fit both the 40mm and 50mm valves?
Yes. Astralpool lists 75906 as the Sightglass - 40mm/50mm - MPV on its Multiport Valve - Sep 09 - Current parts list, and on both the 50mm 76053 and the 40mm 76036 valve diagrams.
Does the sight glass come with a gasket?
No. This listing is the sight glass only. The gasket is Astralpool part 75917, sold separately, or you can order both together as the Sight Glass with Seal. Fit a new gasket whenever the sight glass comes out, because an old gasket can weep against a new glass.
Which filters use it?
Astralpool lists it on the 50mm valve 76053 (CA300, CA340, CA400) and the 40mm valve 76036 (ECA550, ECA650), and the CA280 runs the 40mm CA valve 76044. Australian parts suppliers also list it for the Astral EC 40mm valve 76037 (EC550, EC650) and for Hurlcon and Astralpool RX, E and FG series valves made from September 2009.
Will it fit an older valve?
It is listed for valves made from September 2009 onwards. Hurlcon valves made before September 2007 take a different sight glass, 75073. If your valve was made before September 2009, or you are not sure, send us a photo and we will confirm what fits.
Does it fit Zodiac or APV fibreglass filters?
Not as listed. Astralpool's catalogue lists Zodiac sight glass with o-ring W89280104 for the 50mm Zodiac top mount valve on APV700, APV800 and APV900 filters, and a 40mm union with sight glass, W89280101, for the APV650.
I can see water moving in the sight glass while the valve is on Filter. Is the sight glass faulty?
No. The sight glass is showing you an internal leak. Water reaching the waste side of the valve on Filter usually means a worn spider gasket: 75916 on 40mm valves, 75929 on 50mm valves.
Is this a genuine Astralpool part?
Yes. Heater and Spa Parts is an authorised Fluidra dealer and warranty agent, and this is the genuine Astralpool 75906.
Manufacturer Catalogues, Diagrams & Part Numbers: Need exploded views, spare part numbers, product numbers, diagrams, or more product information? See the manufacturer catalogues below. In the Astralpool Catalogue 2026 spare parts section for filters, the sight glass is No. 17 on the Multiport Valve - Sep 09 - Current list (page 81), No. 18 on the 50mm Multiport with Gauge diagram (76053, page 82) and No. 20 on the 40mm Multiport Assembly diagram (76036, page 83).
Important Before Ordering: Please ensure you order correctly. Confirm this product is suitable before ordering. Use the catalogues above, seek professional assistance, or contact us with photos of your existing part, model details, serial numbers, and any labels.
As with all products, these must be diagnosed and fitted by a qualified and experienced person.
Common search terms: Astralpool 75906, 75906 sight glass, Astral MPV sight glass, multiport valve sight glass, sightglass 40mm 50mm, observe lid, backwash sight glass, sand filter sight glass, Hurlcon sight glass, CA300 CA340 CA400 sight glass, ECA550 ECA650 sight glass, 76053 sight glass, 76036 sight glass, 75917 sight glass gasket, WWDG SpaPro.
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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75906
