Can I replace a Dow FilmTec membrane with a Hydranautics equivalent?

Yes. All 4040 and 8040 format membranes follow industry-standard dimensions and are physically interchangeable regardless of manufacturer. A Hydranautics CPA3-LD-4040 can directly replace a Dow FilmTec BW30-4040 in the same pressure vessel without any modifications. Match the active area, rejection rate, and max pressure to your system requirements.

What does the 4040 and 8040 designation mean?

The numbers indicate the physical dimensions of the membrane element. A 4040 element is approximately 4 inches in diameter and 40 inches long. An 8040 element is approximately 8 inches in diameter and 40 inches long. The 4040 format is used in smaller commercial systems, while the 8040 format is standard for industrial and municipal installations.

How often should RO membranes be replaced?

RO membranes typically last 3 to 7 years depending on feed water quality, pre-treatment effectiveness, operating conditions, and cleaning frequency. Signs that replacement is needed include declining permeate flow, increasing salt passage, rising differential pressure, or inability to restore performance through chemical cleaning.

What is the difference between a low-energy and standard brackish water membrane?

Low-energy (LE) and extra-low-energy (XLE) membranes produce the same permeate flow at significantly lower operating pressure, typically 100 to 150 psi versus 200 to 250 psi for standard elements. This reduces pump energy consumption by 20 to 40 percent. Low-energy elements may have slightly lower salt rejection than standard elements, so they are best suited for treating lower-TDS feed water.

RO Membrane Cross-Reference Guide: Find Your Replacement Membrane

Finding a compatible replacement membrane does not require staying with the original manufacturer. This cross-reference guide maps popular reverse osmosis and nanofiltration membrane models across major brands—Dow FilmTec, Hydranautics (Nitto), Toray, LG Chem, and others—so you can identify equivalent elements by membrane area, salt rejection, and application type. ForeverPure stocks compatible replacements for all models listed below.

Use the tables to find your current membrane model, then identify the equivalent element you need. All specifications shown are nominal values at standard test conditions. Contact our membrane specialists for application-specific recommendations.

Brackish Water Membranes – 4040 Format

4040 (4-inch diameter, 40-inch length) brackish water elements are standard for commercial RO systems producing 1,000–20,000 GPD. These elements operate at 150–250 psi and treat feed water from 500 to 10,000 ppm TDS.

Model	Manufacturer	Active Area (ft²)	Rejection (%)	Max Pressure (psi)	Application
BW30-4040	Dow FilmTec	85	99.5	600	General brackish water
CPA3-LD-4040	Hydranautics	85	99.7	600	High rejection brackish
TM720-400	Toray	85	99.7	600	General brackish water
BW 4040 R	LG Chem	85	99.5	600	General brackish water
RE4040-BLN	CSM (Toray)	85	99.5	600	General brackish water
ACM4-4040	TriSep	87	99.5	600	General brackish water
AG-4040F	GE/Suez	85	99.5	600	General brackish water

Brackish Water Membranes – 8040 Format

8040 (8-inch diameter, 40-inch length) elements are the workhorse of industrial and municipal brackish water RO. A single 8040 element produces 7,000–12,000 GPD depending on the model and operating conditions.

Model	Manufacturer	Active Area (ft²)	Rejection (%)	Max Pressure (psi)	Application
BW30-400	Dow FilmTec	400	99.5	600	General brackish water
BW30-400/34i	Dow FilmTec	400	99.5	600	High flow brackish
ESPA2-LD-8040	Hydranautics	400	99.6	600	Low-energy brackish
CPA5-LD-8040	Hydranautics	400	99.7	600	High rejection brackish
TM720D-400	Toray	400	99.7	600	General brackish water
BW 8040 R	LG Chem	400	99.5	600	General brackish water
RE8040-BLN	CSM (Toray)	400	99.5	600	General brackish water
AG-8040F	GE/Suez	400	99.5	600	General brackish water

Seawater Membranes – 4040 Format

4040 seawater elements are used in small desalination systems from 2,000 to 25,000 GPD. They operate at 800–1,000 psi and reject 99.5%+ of salt from seawater with 35,000 ppm TDS.

Model	Manufacturer	Active Area (ft²)	Rejection (%)	Max Pressure (psi)	Application
SW30-4040	Dow FilmTec	80	99.4	1,000	Standard seawater
SWC4+	Hydranautics	80	99.8	1,200	High rejection seawater
SWC5	Hydranautics	85	99.8	1,200	High area seawater
TM820C-400	Toray	80	99.75	1,200	Standard seawater
SW 4040 R	LG Chem	80	99.7	1,200	Standard seawater
RE4040-SR	CSM (Toray)	80	99.7	1,000	Standard seawater

Seawater Membranes – 8040 Format

8040 seawater elements are the standard for industrial and municipal desalination plants above 25,000 GPD. Each element produces 5,000–8,000 GPD of permeate from seawater feed.

Model	Manufacturer	Active Area (ft²)	Rejection (%)	Max Pressure (psi)	Application
SW30HR-380	Dow FilmTec	380	99.7	1,200	High rejection seawater
SW30HRLE-400i	Dow FilmTec	400	99.8	1,200	Low energy seawater
SW30XHR-400i	Dow FilmTec	400	99.82	1,200	Extra high rejection
SWC6-LD	Hydranautics	440	99.8	1,200	High area seawater
SWC5-LD	Hydranautics	400	99.8	1,200	Standard seawater
TM820M-400	Toray	400	99.75	1,200	Standard seawater
TM820V-400	Toray	400	99.8	1,200	High rejection seawater
SW 8040 R	LG Chem	400	99.8	1,200	Standard seawater
RE8040-SHN	CSM (Toray)	400	99.8	1,200	Standard seawater

Low-Energy (LE/XLE) Membranes – 4040 Format

Low-energy and extra-low-energy membranes operate at reduced pressure (100–150 psi) while maintaining high rejection. They are ideal for treating low-TDS brackish water, municipal tap water polishing, and applications where energy cost is the primary concern.

Model	Manufacturer	Active Area (ft²)	Rejection (%)	Max Pressure (psi)	Application
XLE-4040	Dow FilmTec	85	99.0	600	Extra low energy
LP-4040	Dow FilmTec	85	99.0	600	Low pressure
ESPA1-4040	Hydranautics	85	99.3	600	Energy-saving
ESPA2-4040	Hydranautics	85	99.6	600	Low energy, high rejection
TMG20-400	Toray	85	99.5	600	Low pressure
LE 4040 R	LG Chem	85	99.0	600	Low energy
RE4040-ELN	CSM (Toray)	85	99.2	600	Extra low energy

Nanofiltration (NF) Membranes – 4040 Format

Nanofiltration membranes operate at lower pressures than RO and selectively remove divalent ions (hardness, sulfate) while allowing monovalent ions (sodium, chloride) to pass partially. They are used for water softening, color removal, and selective demineralization.

Model	Manufacturer	Active Area (ft²)	MgSO4 Rejection (%)	NaCl Rejection (%)	Application
NF90-4040	Dow FilmTec	85	97	85–95	Tight NF, near-RO rejection
NF270-4040	Dow FilmTec	85	97	40–60	Loose NF, hardness removal
ESNA1-LF-LD-4040	Hydranautics	85	95	70–85	General nanofiltration
ESNA1-LF2-LD-4040	Hydranautics	85	96	75–90	Enhanced NF
TN410M	Toray	85	95	50–70	Water softening
NE 4040-90	LG Chem	85	97	85–95	Tight NF
NE 4040-70	LG Chem	85	95	40–60	Loose NF

How to Use This Cross-Reference

Find your current membrane model in the appropriate table above based on your element size (4040 or 8040) and feed water type (brackish, seawater, low energy, or NF).
Compare active area and rejection to identify equivalent elements from other manufacturers. Elements with matching area and rejection will perform similarly in your system.
Check max operating pressure to confirm compatibility with your system's high-pressure pump and pressure vessel ratings.
Order the replacement from ForeverPure's membrane catalog or contact us for pricing on bulk membrane orders.

Need Help Selecting the Right Membrane?

If your current membrane model is not listed above, or if you need help determining the best replacement for your specific water chemistry, our membrane specialists can review your system design and water analysis to recommend the optimal element. Browse our full membrane and filter inventory or request a membrane selection consultation.