4" x 40" Freshwater Reverse Osmosis Membrane

A large home or a business running on reverse osmosis cannot afford a slow tank refill or a creeping TDS reading. In Crystal Quest systems from 1,800 to 7,000 GPD, the 4" x 40" elements carry the whole load, so their condition decides how much purified water you get and how good it tastes.

The Crystal Quest 4" x 40" Freshwater Reverse Osmosis Membrane (CQE-RC-04086, the 4040 element size) is the replacement element listed for the 1,800, 4,000, 5,000 and 7,000 GPD Whole House Reverse Osmosis System and the same sizes of the Commercial and Medical Mid-Flow RO Systems. Because 4040 is a standard element size, it also fits other RO systems built for 4 x 40 inch membranes. It is a thin-film composite (TFC) element for pre-filtered, dechlorinated municipal or well water.

At a glance

• Counts by system: one for 1,800 GPD, two for 4,000 GPD, three for 5,000 GPD and four for 7,000 GPD on the Whole House RO
• Published with its test conditions: 99% nominal salt rejection (96% minimum) at 550 ppm, 150 psi, 77°F (25°C) and 15% recovery
• Freshwater class for feed water under 2,000 ppm TDS; brackish and seawater 4040 elements are sold separately
• Service life of 2 to 3 years; actual life depends on feed water quality, system configuration and usage

What you are looking at

The 4040 is the workhorse format of light commercial RO: a 4" diameter, 40" long spiral-wound element. Inside, many leaves of TFC membrane and mesh feed spacer are rolled around a perforated permeate tube. The larger diameter holds far more membrane than a 2.5" element of the same length, which is why one 4040 can carry an entire 1,800 GPD system. A brine seal at the inlet end keeps feed water from bypassing the element. It ships in preservative solution with core tube protectors on each end.

How it works and what keeps it working

Separation under pressure

The system pump pushes feed water across the membrane harder than the osmotic pressure created by its dissolved salts. Water molecules pass into the permeate channels; dissolved ions stay in the feed and leave as concentrate. Crystal Quest rates these elements at 150 psi operating pressure. A Crystal Quest RO system sends about 1 gallon to drain for every 1 to 3 gallons of purified water, depending on your water chemistry and setup.

Clean, then decide

Over time, mineral scale, organics and biological film build up on the membrane surface. Before replacing elements, check whether a cleaning will bring them back. Periodic cleaning can restore performance, but keep cleaning flows within the pressure-drop limits of 13 psi per element and 30 psi per pressure vessel. If rejection does not recover after cleaning, the membrane itself has aged and it is time for new elements.

What it reduces

Primary target: total dissolved solids: hardness minerals, sodium, chloride, sulfate and the other dissolved ions behind scale, spotting and off tastes. Crystal Quest whole house RO systems are rated for 96% minimum and 98.5% nominal salt rejection.

Also held back: particles of every kind, microplastics included, are far too large to pass the membrane; the pre-filters catch most of them first.

Not designed to handle: free chlorine (0.1 ppm maximum), sediment, and iron or manganese above 0.05 ppm. Feed hardness should be under 5 gpg on 1,800 GPD systems and under 15 gpg on 4,000 to 7,000 GPD systems. For salty groundwater or seawater, choose the 4" x 40" Brackish Water or 4" x 40" Seawater Desal element instead.

Why Crystal Quest

• The exact element and count for each Crystal Quest system size, from our own replacement tables.
• Expert support for big systems: help reading your log, deciding clean or replace, and setting up the system again.
• Over 1,000,000 people served since 1994. Crystal Quest builds under ISO 9001 quality management, has made water filtration in the USA for over 30 years and offers lifetime support by phone, email or chat.

Where it fits

• Whole House Reverse Osmosis System: 1,800 GPD (1), 4,000 GPD (2), 5,000 GPD (3), 7,000 GPD (4).
• Commercial Mid-Flow and Medical Mid-Flow RO Systems, 1,800 to 7,000 GPD: use the quantity in your system's replacement table.
• High-Flow RO Systems are also built on 4040 elements; call us to confirm the part for your unit.
• Smaller systems: 750, 1,500 and 2,500 GPD use the 2.5" x 40" element.

RO membranes are not returnable under our refund policy, so check the part number on your current elements or call us before ordering.

Standard 4040 format

This is a low-energy freshwater element in the standard 4040 (4" x 40") format used in 4" x 40" membrane housings and pressure vessels, including Crystal Quest systems. Crystal Quest rates its whole house RO elements at 150 psi operating pressure, well below what brackish water and seawater elements are built for, so the pump does less work on tap and well water. A shared format name is a good start, not a guarantee: if your system is not a Crystal Quest model, compare the brine seal position, permeate tube ends and flow direction with your current element, or contact us before ordering.

Storage and handling

Each element ships sealed in its bag in a preservative solution. Keep it sealed until you are ready to install it, store it indoors out of direct sunlight, and never let it freeze. Once an element has been installed and wetted, do not let it dry out. If your system will sit idle for a season, Membrane Preservative is used to protect the elements against damage from bacterial growth.

Common questions

Element specifications

Element performance

Feed water limits for the system

*Service life is an estimate. Actual life depends on feed water quality, system configuration and usage. Performance figures are from the Crystal Quest whole house RO manuals; production falls with colder or higher-TDS water. Element ratings are from the element data sheet. The 600 psi rating is the element's structural limit. Low energy elements are designed to make their rated flow at about 150 psi.