The Buck (moisture) Stops Here!
Like all compressed air drying systems, each design has its abilities and its limitations.
The Membrane style “point-of-use” air dryer, while not practical for all air dryer applications, due to low CFM capacities, is the perfect air dryer, if the CFM flow rates, inlet pressures, and maximum inlet temperatures fall within the sizing limitations of the Membrane Dryer. The design simple with no moving parts. It is critical to the life expectancy and performance of the dryer that the pre-treatment coalescing filters are correctly sized and maintained. Using no electrical energy and requiring the very minimum of on-going maintenance while supplying exceptional moisture removal makes this design the perfect choice for most low-flow unattended applications.
The Membrane dryer operates on the principle of selective permeation through a membrane.
As the compressed air passes through a bundle of tiny hollow (polysulfone) membrane fibers, water vapor and a portion of the compressed air flow diffuses through the semi-permeable membrane walls while the dried air continues downstream.
The water vapor which has been separated from the compressed air by the differential gas pressure on the inside and outside of the hollow fibers, is purged out of the housing by the sweep air (Purge air).
The Membrane dryer must be used only with clean, oil free air. It must have a coalescing type prefilter installed ahead of the dryer to remove any liquid water, oil and aerosol contaminants from the compressed air stream, as these would block the permeation’s of the fibers, reducing the performance of the dryer.
These dryers are point-of-use dryers, and are sized for low capacities compared to other dryer types. The membrane dryer can be connected in parallel to increase the capacity beyond that of the single dryer.
The advantages of these dryers are:
- There are no moving parts.
- There are no consumables to replace.
- They require no external power source.
- They install directly in the pipeline.
- They can operate in severe environments,
Such as high or low temperatures or corrosive and explosive atmospheres.
- They operate continuously without the need for adjustment or maintenance.
(Other than prefilter maintenance)
- Dewpoint suppression range is between +40 and -40 oF.
The disadvantages of these dryers are:
- They require about 15-20 % purge air. (On some models)
- Membrane dryers reduce the oxygen content of the compressed air, and can not be used in breathing air applications.
Ready to learn about another type of dryer? Check out the Deliquescent Dryer in this post!