MRD50-1B Waterway / Rainbow RDC 50 & Waterco Top Load Filter Cartridge - 340mm x 126mm - 817-5000 - Spatex by Magnum
MRD50-1B Waterway / Rainbow RDC 50 & Waterco Top Load Filter Cartridge - 340mm x 126mm - 817-5000 - Spatex by Magnum 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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MRD50-1B Waterway / Rainbow RDC 50 & Waterco Top Load Filter Ca...
MRD50-1B Waterway / Rainbow RDC 50 & Waterco Top Load Filter Cartridge - 340mm x 126mm - 817-5000 - Spatex by Magnum is temporarily out of stock and will ship as soon as it's available.
Spatex MRD50-1B Waterway / Rainbow RDC 50 & Waterco Top Load Filter Cartridge - 340mm x 126mm - 817-5000
Spatex MRD50-1B replacement pleated filter cartridge, made in New Zealand by Magnum Filters. Suits Waterway and Rainbow RDC50 and RTL50 top load filters, Waterco top load housings, and Jacuzzi J245 and J275 spas. A very common cartridge found on spas dating back more than twenty years.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
Spatex filter cartridges are manufactured by Magnum Filters in New Zealand. Magnum have been producing spa and pool filter cartridges since 1982 and supply OEM and co-branded cartridges to spa manufacturers and distributors worldwide. These are not low-grade generic filters - they use quality pleated filtration media for reliable water flow, solid dirt-holding capacity and consistent service life, and are used throughout the Australian spa industry alongside WWDG and SpaPro style filters.
Specifications
- Height: 338mm to 340mm
- Width: 125mm to 126mm
- Centre hole ID: 54mm to 55mm
- Top: Flat with open hole
- Bottom: Flat with open hole
- Filter area: 50 sqft
- Spatex part number: sx-rd50-1b
- Magnum part number: MRD50-1B
- Country of manufacture: New Zealand
Also Known As
This cartridge is sold under a number of OEM, distributor and aftermarket part numbers, including: MRD50-1B, MRD50, MRA50-1B, 817-5000, FAA309, FC-FAA309, FC-237, WWDG 309, SpaPro 339, Unicel C-4950, FC2390, PRB50-IN, Guardian 413-212-02, RFILADF50B.
Commonly Suits
- Waterway top load and in-line filters
- Waterco top load filters
- Rainbow RDC and RTL filter housings
- Jacuzzi J245 and J275
- Various Chinese-manufactured spas using 50 sqft top load filtration
Spa brand alone is not enough to identify a filter. Manufacturers frequently change filtration systems between models and production years, so always compare your existing cartridge before ordering.
Before You Order
This cartridge can also be used in place of the RDC25. It is the same physical size but carries more pleats, so it gives more filtration area in the same housing.
Measure the overall length, the outside diameter, the top style and the bottom connection and compare them against this listing. If you are unsure, send us a photo and the measurements of your old cartridge and we will confirm the correct replacement.
Filter Replacement Guide
Spa filters should generally be replaced every 1 to 2 years, depending on usage, water quality, chemical balance and cleaning routine. Rinsing the pleats regularly and soaking the cartridge in a dedicated filter cleaner will extend its working life between replacements.
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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