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RO Membrane Housing Sizes Explained (2540, 4040, 8040) With Prices
- Code = diameter + length in inches (4040 = 4" × 40")
- 8040 membranes give about four times the flow of 4040
- Housing length sets how many membranes it holds (e.g. 40120 = three 4040s)
- Stainless or FRP; end port or side port
On this page
- What Is the Difference Between 4040 and 8040 Membranes?
- How Many Membranes in a Housing?
- Stainless Steel Membrane Housings: End Port
- Stainless Steel Membrane Housings: Side Port
- FRP Membrane Housings (4040 and 8040, Multi-Core)
- Stainless or FRP Housing?
- Replacement Membranes
- How to Install an RO Membrane in a Housing
- Frequently asked questions
What Is the Difference Between 4040 and 8040 Membranes?
An 8040 membrane is twice the diameter of a 4040, so it has much more membrane area and gives roughly four times the output. Small and medium plants use 4040s; large plants use 8040s. The housing must match the membrane diameter.
How Many Membranes in a Housing?
| Housing code | Holds |
|---|---|
| 4021, 4040 | One 21" or one 40" membrane |
| 4080 | Two 4040 membranes |
| 40120 | Three 4040 membranes |
| 40160 | Four 4040 membranes |
| FRP 4040-2, -3, -4 / 8040-1 to -7 | The number after the dash = number of membranes ("cores") |
Stainless Steel Membrane Housings: End Port
End Port 2514(2.5"seamless) Stainless Steel Membrane HousingKSh 9,825
End Port 2521 (2.5"seamless) Stainless Steel Membrane HousingKSh 13,755
End Port 2540 (2.5"seamless) Stainless Steel Membrane HousingKSh 17,816
End Port 4014 (4"seamless) Stainless Steel Membrane HousingKSh 10,218
End Port 4021 (4"seamless) Stainless Steel Membrane HousingKSh 12,969
End Port 4040(4"seamless) Stainless Steel Membrane HousingKSh 18,078
End Port 40120(4"seamless) Stainless Steel Membrane HousingKSh 51,090
End Port 40160(4"seamless) Stainless Steel Membrane HousingKSh 72,705Current listed prices incl. VAT (updated 1 October 2026).
Stainless Steel Membrane Housings: Side Port
Current listed prices incl. VAT (updated 1 October 2026).
FRP Membrane Housings (4040 and 8040, Multi-Core)
| Product | Price |
|---|---|
| FRP End Port 4040-1 Membrane Housing | KSh 13,755 |
| FRP End Port 4040-2 Core Membrane Housing | KSh 21,719 |
| FRP End Port 4040-3 Core Membrane Housing | KSh 27,247 |
| FRP End Port 4040-4 Core Membrane Housing | KSh 33,171 |
| FRP side Port 8040-1 Core Membrane Housing | KSh 67,131 |
| FRP side Port 8040-2 Core Membrane Housing | KSh 73,055 |
| FRP side Port 8040-3 Core Membrane Housing | KSh 82,927 |
| FRP side Port 8040-4 Core Membrane Housing | KSh 96,748 |
| FRP side Port 8040-5 Core Membrane Housing | KSh 108,595 |
| FRP side Port 8040-6 Core Membrane Housing | KSh 125,152 |
| FRP side Port 8040-7 Core Membrane Housing | KSh 141,338 |
Current listed prices incl. VAT (updated 1 October 2026).
Stainless or FRP Housing?
Stainless housings are strong and look neat on skid-mounted plants. FRP (fibreglass) housings resist corrosion, including from salty water, and are common on larger plants. Both must be rated for your plant's operating pressure.
Replacement Membranes
| Product | Price |
|---|---|
| LP-4040 RO Membrane | KSh 23,670 |
| LP21-4040 RO Membrane | KSh 33,405 |
| ESPA2-4040 RO Membrane | KSh 62,400 |
| LP-8040 Membrane | KSh 102,570 |
Current listed prices incl. VAT (updated 1 October 2026).
How to Install an RO Membrane in a Housing
- Flush the housing clean and lubricate the O-rings and brine seal with a food-grade lubricant.
- Push the membrane in with the brine seal at the feed end, facing the flow.
- Fit the end caps and connectors, then flush the new membrane before use.
Related: membrane replacement cost and industrial RO plants.
Watch: RO purifiers and water ATMs
Frequently asked questions
What is a 4040 RO membrane?
A membrane 4 inches in diameter and 40 inches long; the code gives diameter and length in inches.
What is the difference between 4040 and 8040 membranes?
An 8040 is 8 inches across and gives roughly four times the output of a 4040; the housing must match.
What is a membrane housing?
The pressure vessel that holds RO membranes and connects them to the plant.
What is the difference between end port and side port housings?
End port housings connect through the end caps; side port housings connect on the side, which makes multi-housing manifolds neater.
How many membranes fit in a 40120 housing?
Three 4040 membranes (120 inches of length).