4" x 40" Freshwater RO Replacement 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

Which systems use the 4" x 40" element?

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.

How many elements do I need?

Use the count in your system's replacement table. On the Whole House Reverse Osmosis System it is one for 1,800 GPD, two for 4,000 GPD, three for 5,000 GPD and four for 7,000 GPD.

Is this a standard 4040 RO membrane?

It is a 4" x 40" element, the 4040 format. Fit is about more than the format name, so order by the part number your Crystal Quest system lists, or call us to confirm.

Should I clean or replace my 4040 membranes?

If performance dropped because of scale or fouling, a cleaning can bring it back. If rejection stays low after cleaning and fresh pre-filters, replace the elements.

How long do they last?

Plan on 2 to 3 years. Actual life depends on feed water quality, system configuration and usage.

Do I need to flush a new element?

Yes. New elements ship in a preservative solution. Flush for at least 1 hour and discard all permeate and concentrate made during the flush.

Freshwater, brackish or seawater?

This is the freshwater element. Crystal Quest also sells 4" x 40" brackish water and seawater desal elements. Choose the class your system and feed water are designed for, and ask Crystal Quest if you are unsure.

Specifications for your selection

Single

SKU: CQE-RC-04086
Diameter (width): 4.0 in
Length (height): 40.0 in
Replace every: 2 to 3 years

Membrane type: Thin-film composite (TFC) reverse osmosis element
Application: Freshwater
Element size: 4" x 40"
Part number: CQE-RC-04086
Listed replacement for: Whole House Reverse Osmosis System 1,800 GPD (1), 4,000 GPD (2), 5,000 GPD (3), 7,000 GPD (4); Commercial and Medical Mid-Flow RO Systems 1,800 to 7,000 GPD (quantity per system table)
Feed water: Pre-filtered and dechlorinated; free chlorine 0.1 ppm maximum
Rated production: 2,500 GPD at 150 psi, 550 ppm feed, 77°F (25°C), 15% recovery; actual output drops with colder or saltier water
Nominal salt rejection: 99% (96% minimum) at 550 ppm feed, 150 psi, 77°F (25°C), 15% recovery
Operating pressure: Rated maximum: 600 psi; suggested operating range: 100 to 150 psi
Pressure note: 600 psi is the element's structural limit; low energy elements are designed to make their rated flow at about 150 psi
Maximum pressure drop: 13 psi per element; 30 psi per pressure vessel
Start-up: Flush at least 1 hour; discard all permeate and concentrate from the flush
Replacement interval: 2 to 3 years; actual life depends on feed water quality, system configuration and usage
Format: Standard 4040 element; compare brine seal position and tube ends if your system is not a Crystal Quest model
Storage: Keep sealed until installation, out of direct sunlight; do not let it freeze, and do not let an installed element dry out

Performance curves

Rated 2,500 GPD at 77°F (25°C), 150 psi, 550 ppm feed.

Figure 1. Permeate flow vs feed temperature at 100, 125 and 150 psi, normalized to the rated flow at 77°F (25°C) and 150 psi.

Data for Figure 1

Expected permeate flow in GPD by feed temperature and feed pressure
Feed temperature	100 psi	125 psi	150 psi
40°F (4°C)	766	973	1,180
50°F (10°C)	949	1,200	1,460
60°F (16°C)	1,170	1,480	1,790
70°F (21°C)	1,420	1,800	2,190
77°F (25°C)	1,620	2,060	2,500
85°F (29°C)	1,850	2,350	2,850
95°F (35°C)	2,160	2,750	3,330

Values in GPD (gallons per day).

Figure 2. Permeate flow vs feed pressure at 50, 60 and 77°F. Flow follows net driving pressure, the feed pressure minus the feed's osmotic pressure (about 7 psi for the 550 ppm test feed). Shaded: suggested operating range, 100 to 150 psi.

Data for Figure 2

Expected permeate flow in GPD by feed pressure and feed temperature
Feed pressure	50°F (10°C)	60°F (16°C)	77°F (25°C)
25 psi	180	221	309
50 psi	436	536	747
75 psi	693	851	1,190
100 psi	949	1,170	1,620
125 psi	1,200	1,480	2,060
150 psi	1,460	1,790	2,500

Values in GPD (gallons per day).

Crystal Quest engineering data. Typical values calculated from the element's rated output at standard test conditions; actual output depends on feed water, recovery and element condition.

Element specifications

Specification	Value
Membrane type	Thin-film composite (TFC) reverse osmosis element
Application	Freshwater
Element size	4" x 40"
Part number	CQE-RC-04086
Listed replacement for	Whole House Reverse Osmosis System 1,800 GPD (1), 4,000 GPD (2), 5,000 GPD (3), 7,000 GPD (4); Commercial and Medical Mid-Flow RO Systems 1,800 to 7,000 GPD (quantity per system table)
Feed water	Pre-filtered and dechlorinated; free chlorine 0.1 ppm maximum
Start-up	Flush at least 1 hour; discard all permeate and concentrate from the flush
Service life	2 to 3 years*

Element performance

Rated production	2,500 GPD at 150 psi, 550 ppm feed, 77°F (25°C), 15% recovery; actual output drops with colder or saltier water
Nominal salt rejection	99% (96% minimum)
Test conditions	550 ppm feed, 150 psi, 77°F (25°C), 15% recovery
Operating pressure	Rated maximum: 600 psi; suggested operating range: 100 to 150 psi
Maximum temperature	113°F (45°C)
pH range	Rated 2 to 11; suggested 5 to 11 for continuous operation; cleaning 2 to 12
Free chlorine tolerance	0.1 ppm maximum. Remove chlorine and chloramine before the membrane with carbon pre-filtration (Crystal Quest whole house RO systems include this).
Maximum turbidity	1 NTU
Silt density index	Less than 5 SDI
Maximum pressure drop	13 psi per element; 30 psi per pressure vessel

Feed water limits for the system

Total dissolved solids	Under 2,000 ppm
Hardness	Under 5 gpg (1,800 GPD); under 15 gpg (4,000 to 7,000 GPD)
Iron and manganese	Under 0.05 ppm each
Silica and organics	Under 1 ppm each
Free chlorine	None (remove upstream)
Feed temperature	40°F to 105°F

*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.

Illustration of a Crystal Quest freshwater reverse osmosis membrane element

When: plan on every 2 to 3 years; actual life depends on feed water quality, system configuration and usage. On well pre-treated water, rejection usually holds for two to three years, while flow can dip slightly after the first.
Track it: log feed and product TDS, pressures and flows. Rejection = (feed TDS minus product TDS) divided by feed TDS.
Replace as a set: on multi-element systems, change all elements together so they share the load evenly.
Start-up and routine: flush new elements at least 1 hour, discarding permeate and concentrate, then flush the system weekly.
Pre-filters: change them typically every 12 to 24 months, about 18 months for most homes, and yearly on chlorinated city water. The 4000/5000 GPD Whole House RO Filter Pack holds all three for those sizes.

How to replace it

With the system shut down, remove the end caps from the top of the membrane housings (snap ring or clamp bolts, depending on the housing).
Pull the used element out of the top of the housing; heavy-duty or channel-lock pliers may be needed.
Open the new element bag close to the seal, then remove the element and the core tube protectors from each end.
Inspect the brine seal and permeate tube for nicks or cuts, and replace damaged O-rings or brine seals.
Lubricate the brine seal with a food-grade lubricant and install the brine seal end first, following the housing flow direction.
Insert the element at a slight angle with a slow twisting motion so the brine seal stays in its groove, and push it fully into the housing.
Refit the end caps without pinching the O-rings, reinstall the snap ring or clamp, and reconnect any fittings.
Flush the new element for at least 1 hour, discarding all permeate and concentrate, then return the system to service as its manual directs.

Shutdowns and storage

Before a system is shipped or stored, clean it, flush it and protect the elements with a solution made for membrane elements, then drain the housings and lines completely so nothing can freeze and crack.

Plan ahead on a large system. Choose Subscribe and Save above for 7% off on the schedule you choose.

Listed as the replacement membrane (CQE-RC-04086) for the 1,800, 4,000, 5,000 and 7,000 GPD Crystal Quest Whole House Reverse Osmosis System, which uses one, two, three and four elements respectively.

The Commercial and Medical Mid-Flow Reverse Osmosis Systems also list this element for their 1,800 to 7,000 GPD sizes. Order the quantity shown in your system's replacement table, and match diameter, length and application class.