Franklin FWME4021RO-XLP Extra Low Pressure RO Membrane

Compact 4021 4-Inch RO Membrane for Mid-Output Commercial Systems

If you have outgrown a 2.5-inch element but cannot fit a full 40-inch membrane, the Franklin Water FWME4021RO-XLP reverse osmosis membrane splits the difference. This compact 4 x 21 extra-low-pressure 4021 membrane produces 1,150 GPD at just 150 psi with 99% salt rejection. NSF/ANSI 61 certified for drinking water contact and rated for feed water up to 2,000 mg/L TDS.

Quick Specs

• Membrane Type: Thin-Film Composite (TFC), Extra Low Pressure

• Element Size: 4" x 21" (standard 4021 format)

• Active Membrane Area: 36 ft² (3.3 m²)

• Permeate Flow Rate: C (4.35 m³/d)

• Stabilized Salt Rejection: 99%

• Maximum Operating Pressure: 600 psi (4.14 MPa)

• Maximum Feed TDS: 2,000 mg/L

• Certification: NSF/ANSI 61

Key Features and Benefits

• Produces 1,150 GPD from 36 ft² of active membrane area, nearly three times the output of a 2521 element in the same 21-inch length. If your current system caps out at 400-750 GPD, this space-saving 1,150 GPD RO membrane is the next step up without a longer housing.

• Operates at 150 psi test pressure on feed water up to 2,000 mg/L TDS. That is roughly 35% less pressure than standard 225-psi brackish water elements, which cuts pump sizing and electricity costs. As an energy-efficient commercial reverse osmosis membrane, it pays for itself as an energy-saving choice over the full service life.

• 99% stabilized salt rejection across groundwater, surface water, and municipal sources. This 4021 RO membrane handles drinking water production, lab pre-treatment, boiler feed water, and cooling tower makeup from a single element.

• NSF/ANSI 61 certified. Meets health-effects requirements for materials in contact with drinking water.

• Standard 4021 format fits any compatible 4-inch pressure vessel. At 21 inches, this compact 4-inch RO membrane runs half the length of a standard 4040 reverse osmosis membrane, fitting into tighter equipment layouts as a low-energy commercial RO membrane without a housing change.

• Maximum feed flow of 3.6 m³/h (15.9 gpm) with a cleaning pH range of 1 to 13. Aggressive CIP (clean-in-place) cycles restore water flow and extend membrane life without pulling the element from the vessel.

FWME4021RO-XLP Specifications

Applications

• Mid-capacity commercial RO systems in space-constrained equipment rooms

• Office buildings and commercial facilities stepping up from 2.5-inch RO systems

• Laboratory pure water preparation where a 4040 housing will not fit

• Boiler feed water and cooling tower makeup treatment

• Water vending machines and high-output self-serve refill stations

• Pre-treatment stage for high-purity water production

• Surface water and groundwater treatment for sources up to 2,000 mg/L TDS

Industries

• Commercial water treatment

• Food and beverage production

• Laboratories and research facilities

• Hospitality and facility management

• Light industrial process water

Buy the Franklin Water FWME4021RO-XLP Online from Cleanflow

The FWME4021RO-XLP fills a gap that most membrane lineups leave open: 4-inch-class output in a 21-inch element. If your system has outgrown 2.5-inch membranes but a 4040 will not fit, this is the membrane to spec. 

Cleanflow Utility Supply Company is an authorized Franklin Water Treatment distributor. The FWME4021RO-XLP, compatible reverse osmosis system accessories, and replacement parts ship across Canada and the USA. Returns accepted within 30 days at returns.cleanflow.net.

Frequently Asked Questions

Can I replace a 4040 membrane with a 4021?

No. The Franklin Water 4021 membrane is 21 inches long, and the 4040 is 40 inches long. They require different pressure vessel housings. If you currently run a 4040 system, you would need a shorter 4021-compatible housing to make the switch. The 4021 is intended for new installations or systems already using 4021-format housings, not as a drop-in 4040 replacement.

How much more output does a 4021 give compared to a 2521?

The Franklin Water 4021 XLP is a 1,150 GPD RO membrane with 36 ft² of active area. A 2521 ULP produces 400 GPD from 14 ft². That is nearly three times the output in the same 21-inch length, because the 4-inch diameter provides more than double the membrane surface area. Both fit 21-inch housings, but the 4021 requires a 4-inch vessel.

What does XLP mean on an RO membrane?

XLP stands for extra low pressure. These XLP RO membranes produce their rated output at lower feed pressures than standard commercial elements, which means smaller pumps and lower electricity costs. ULP (ultra-low pressure) membranes work on the same principle. Both target energy-efficient operation on low-salinity feed water, and the naming varies by manufacturer.

What pump do I need for a 4 x 21 reverse osmosis membrane?

The FWME4021RO-XLP produces its rated 1,150 GPD at 150 psi with 1,500 mg/L NaCl feed water. Your pump needs to deliver at least 150 psi at the membrane face and support a maximum feed flow of 3.6 m³/h (15.9 gpm). Actual pressure requirements depend on your feed water TDS and temperature. Consult your system integrator for exact pump specifications.

What happens if I skip pre-treatment on this membrane?

Chlorine destroys thin-film composite membranes. Feed water with more than 0.1 mg/L free chlorine will cause irreversible oxidation damage that no amount of cleaning can fix. High particulate levels (SDI above 5) foul the membrane surface and reduce output. At a minimum, install a carbon pre-filter for chlorine and a sediment filter for particulates. Cleanflow stocks compatible reverse osmosis filters for both stages. For hard water, add a softener or antiscalant dosing system (a chemical that prevents mineral buildup on the membrane surface).