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The 4021 reverse osmosis (RO) membrane is a widely adopted industry-standard membrane element used in commercial and light industrial water treatment systems.
The Origin of “4021”
In international membrane industry standards, the numerical designation represents the physical dimensions of the element.
- “40”: Indicates a nominal outer diameter of 4.0 inches (approximately 101.6 mm).
- “21”: Indicates a nominal length of 21 inches (approximately 533.4 mm).
Description
- High Spatial Flexibility
It serves as an excellent alternative to 4040 membranes in system configurations where water demand is moderate but frame height or width is highly restricted.
- High Standardization
As an internationally recognized standard size, it is fully compatible with global brands, making element replacement and housing procurement (FRP or stainless steel pressure vessels) highly convenient.
- Cost-Effectiveness
For small-flow systems, utilizing 4021 membranes prevents performance redundancy and over-specification, significantly lowering initial capital investment.
Performance Parameters
| Model | 4021 |
| Effective Membrane Area | 36 ft² (3.3 m²) |
| Average Permeate Flow | 950 GPD (3.6 m³/day) |
| Salt Rejection | 99% |
| Max. Inflow Temperature | 8°C |
| Max. Water Flow | 14 GPM (3.2 m³/h) |
| Operating Pressure | 150 psi (1.03 MPa) |
| Max. Operating Pressure | 600 psi (4.2 MPa) |
| Max. Water Temperature | 45°C |
| Max. Feed Water SDI15 | 5 |
| Free Chlorine Concentration | <0.1 mg/L |
| Continuous Operating pH Range | 3–10 |
| Chemical Cleaning pH Range | 2–11 |
| Max. Pressure Drop per Membrane Element | 15 psi (0.1 MPa) |
Applications
Due to its compact size and moderate output capacity, the 4021 RO membrane is extensively utilized in commercial and light industrial water purification sectors.
- Commercial Drinking Water Systems
Centralized pure water systems for schools, hospitals, office buildings, and hotels.
- Light Industrial Process Water
Pretreatment for laboratory ultra-pure water systems, and rinse water for electronics or surface-plating industries.
- Food & Beverage Industry
Small-scale bottled water plants, commercial food service, and pre-filtration for commercial coffee brewing equipment.
- Mobile & Marine Water Desalination
With a length of only ~53 cm, it is a preferred choice for space-constrained RVs, yachts, and mobile emergency water purification units.