2.5" x 40" Freshwater Reverse Osmosis Membrane

Is your whole house or commercial RO making less water than it used to, or is the product TDS climbing? In a 750 to 2,500 GPD Crystal Quest system, the 2.5" x 40" elements do the purifying. When they tire, the storage tank refills more slowly and the water loses that clean, neutral taste.

The Crystal Quest 2.5" x 40" Freshwater Reverse Osmosis Membrane (CQE-RC-04109, the 2540 element size) is the replacement element listed for the 750, 1,500 and 2,500 GPD Whole House Reverse Osmosis System and the same sizes of the Commercial and Medical Mid-Flow RO Systems. Because 2540 is a standard element size, it also fits other RO systems built for 2.5 x 40 inch membranes. It is a thin-film composite (TFC) element for pre-filtered, dechlorinated tap or well water.

At a glance

• Counts by system: one for 750 GPD, two for 1,500 GPD, three for 2,500 GPD on the Whole House RO
• Rated the way engineers compare elements: 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 elements are sold separately
• Built to last: 2 to 3 years of service; actual life depends on feed water quality, system configuration and usage

What you are looking at

A 40" spiral-wound element. Leaves of TFC membrane, separated by a mesh feed spacer, wrap around a perforated permeate tube that runs the full length. Feed water enters one end and travels along the spacer channels; purified water passes through the membrane and spirals into the center tube, while the concentrate leaves the far end carrying the rejected minerals. The brine seal at the inlet end forces every gallon through the element instead of around it. Each element ships wet in preservative, with core tube protectors on both ends.

How it purifies water

Pressure against osmosis

Dissolved salts create osmotic pressure that pulls water toward the saltier side of a membrane. The system pump overcomes that pull, driving water through the membrane while the dissolved ions stay in the feed stream. Crystal Quest rates these elements at 150 psi operating pressure.

Why there is a drain line

The concentrate stream sweeps the membrane surface clean as it flows, which is how an element runs for years without clogging like a cartridge. A Crystal Quest RO system sends about 1 gallon to drain for every 1 to 3 gallons of purified water, set to your water chemistry. Higher feed TDS calls for a more conservative setting; the manual suggests an auto flush upgrade when feed TDS is above 500 ppm.

Why winter output drops

Cold water moves through the membrane more slowly, and higher TDS raises the osmotic pressure the pump has to beat. The same system can need noticeably more pressure in a cold-water climate to make its rated output, which is why our sizing is based on winter water temperature.

What it reduces

Primary target: dissolved solids (TDS): the hardness minerals, sodium, chloride and sulfate that cause scale, spotting and salty or mineral taste. Crystal Quest whole house RO systems are rated for 96% minimum and 98.5% nominal salt rejection.

Also held back: any particle that reaches the membrane, microplastics included, is far too large to pass. Pre-filters remove most of them first.

Not designed to handle: free chlorine (0.1 ppm maximum, so remove it upstream), sediment, and iron or manganese above 0.05 ppm. Feed hardness for 500 to 2,500 GPD systems should be under 5 gpg; harder water scales the membrane, so soften first. Brackish feed needs the 2.5" x 40" Brackish Water Reverse Osmosis Membrane, and seawater needs the 2.5" x 40" Seawater Desal Reverse Osmosis Membrane.

Why Crystal Quest

• The listed element and count for your Crystal Quest system, straight from our replacement tables.
• Complete specs: rejection with test conditions, operating limits and feed water limits in the Specifications tab.
• 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: 750 GPD (1), 1,500 GPD (2), 2,500 GPD (3).
• Commercial Mid-Flow and Medical Mid-Flow RO Systems, 750 to 2,500 GPD: use the quantity in your system's replacement table.
• Not this element: 500 and 1,000 GPD use the 2.5" x 21" element; 1,800 GPD and up use the 4" x 40" element.

RO membranes are not returnable under our refund policy. Confirm the part number on your current element, or call us and we will confirm it with you.

Standard 2540 format

This is a low-energy freshwater element in the standard 2540 (2.5" x 40") format used in 2.5" 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