When it comes to ultrafiltration water purifiers in China, we always hear users keep talking about external pressure membrane and internal pressure membrane.
But what exactly do they mean?
We’ve noticed that many customers often confuse the materials and water filtration accuracy of the internal pressure membrnes and external pressure membranes. Today, I have created an infographic to help everyone understand the key differences between them.
Typically, external pressure membranes are made of PVDF membrane with support layer, boasting a filtration accuracy of 0.1 μm.
(PS: the left on in the above picture, the filter cartridge consists of flexible hollow tubular PVDF membrane fibers with a support layer. The fibers are uniformly distributed with water-permeable micropores of 0.1μm in diameter. Impurities in water such as mud, sediment, and colloids, which have a diameter larger than 0.1μm, cannot pass through the micropores and are thus trapped on the surface of the membrane fibers.)
In contrast, internal pressure membranes are crafted from PVC ultrafiltration membrane, with a much finer filtration accuracy of 0.01 μm.
(PS: the right on in the above picture, the filter cartridge consists of flexible hollow tubular PVC ultrafiltration membrane fibers. The fibers are uniformly distributed with water-permeable micropores of 0.01μm in diameter. Impurities in water such as mud, rust, colloids, bacteria, and viruses, which have a diameter larger than 0.01 microns, cannot pass through the micropores and are thus trapped on the inner wall of the membrane fibers.)
A common myth is that a single ultrafiltration membrane can have a variable accuracy range of 0.1~0.01 μm. However, the filtration accuracy of a single ultrafiltration membrane is fixed, it is either 0.1 μm or 0.01 μm. Since 0.1 μm and 0.01 μm differ by a factor of 10, this discrepancy does not fall under the category of error.
In fact, a 0.1 μm filtration accuracy almost always indicates an external pressure membrane, while a 0.01 μm rating refers to an internal pressure membrane.
Given the 10-fold difference in their filtration precision, there is a strict professional definition in the industry: only PVC membranes with a 0.01 μm filtration accuracy can be defined as true ultrafiltration membranes. Meanwhile, PVDF membranes with support layer (0.1 μm filtration membrane) are categorized as microfiltration membranes.
External pressure membranes are primarily used in the whole house water filtration system, being installed on the main water inlet pipe for whole-house water purification. They excel at filtering impurities such as sediment, rust, colloids, and eggs from turbid water sources like well water, rural muddy water, stream water, and mountain spring water, effectively clarifying the water. Of course, they are also suitable for treating municipal tap water.
The advantage of filter cartridges made of external pressure membranes is that, it can be cleaned repeatedly through regular manual washing to extend their service life. However, the downside is that some user would find manual washing rather cumbersome.
Internal pressure membranes are also ideal for whole-house water purification when installed on the main inlet pipe, take the ChengrongEra Intelligent Ultrafiltration Water Filtration System as an example. Beyond water clarification, it can also eliminate bacteria and viruses from water, elevating the purity of water flowing into household pipelines to a higher level.
In addition to whole-house purification, 0.01 μm internal pressure membranes are widely used in Mineral-retaining kitchen water purifiers.
For kitchen applications, an activated carbon filter would be added before the ultrafiltration membrane to enhance water taste. This combination of activated carbon and ultrafiltration would also produce high-quality mineral-retaining water, perfect for daily drinking. This filtration process is particularly effective for municipal tap water, ensuring the resulting mineral-retaining water is not only clean, but also beneficial to health.
It’s worth noting that the internal pressure membranes used in our kitchen water purifiers are different from those for whole-house purification.
The internal pressure membrane in our mineral-like water kitchen purifiers is a self-developed residual chlorine-removing ultrafiltration membrane by Chengrong Factory. On top of intercepting particulate impurities, bacteria, and viruses, it is specially engineered to remove residual chlorine from water, guaranteeing the purified water achieves a genuine mineral-like quality.
Unlike RO reverse osmosis membranes, Chengrong’s proprietary residual chlorine-removing ultrafiltration membrane retains the natural minerals and trace elements (also known as electrolytes) present in water. These naturally occurring minerals, such as calcium and magnesium, are not only more easily absorbed by the human body but also work synergistically to promote better health. This makes our water purifiers especially suitable for households with elderly family members and young children.
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