page_title: Compressed air dryer
section_title: Membrane dryer
hierarchical_section_title: Compressed air dryer / Membrane dryer
caption_attribution_description: English: Schematic representation of a membrane type compressed air dryer.
context_page_description: Compressed air dryers are special types of filter systems that are specifically designed to remove the water that is inherent in compressed air. The process of compressing air raises its temperature and concentrates atmospheric contaminants, primarily water vapor. Consequently, the compressed air is generally at an elevated temperature and 100% relative humidity. As the compressed air cools, water vapor condenses into the tank, pipes, hoses and tools that are downstream from the compressor. Water vapor is removed from compressed air to prevent condensation from occurring and to prevent moisture from interfering in sensitive industrial processes.
  Excessive liquid and condensing water in the air stream can be extremely damaging to equipment, tools and processes that rely on compressed air. The water can cause corrosion in the tank and piping, wash out lubricating oils from pneumatic tools, emulsify with the grease used in cylinders, clump blasting media and fog painted surfaces. Therefore, it is desirable to remove condensing moisture from the air stream to prevent damage to equipment, air tools and processes.
context_section_description: Membrane dryer refers to a dehumidification membrane that removes water vapor from compressed air. Membrane dryers operate on the principle of migration.  The compressed air to be dried is passed over a membrane that has a high affinity for water vapor.  The water vapor builds on the membrane and migrates through to the opposite or low pressure, side.  A dry cover gas is flowed across the low pressure side and absorbs the water on the membrane.  After absorbing the water, the cover gas is discharged to the atmosphere.  The cover gas is generally taken from the output of the dryer.  The membrane is typically a series of small tubes collected in a bundle within an outer housing.
  Some dryers are non-porous, which means they only permeate water vapor. Non-porous membranes' drying power is only a function of flow rate, pressure. The sweep flow is strictly controlled by an orifice and is not a function of temperature. Porous membranes are modified nitrogen membranes and pass air as well, usually changing the composition of the compressed air by reducing the oxygen content. The only maintenance required is changing the prefilter cartridge twice a year. The performance of porous membranes are dependent on temperature as well as operating pressure and flow.
  Membrane air dryers depress the incoming dew point. Most dryers have a challenge air dew point and pressure specification. So if the inlet dew point is lower than the specified challenge air then the outlet dew point is even lower than specified. For example, a dryer could be rated at a -40 °C (−40 °F) dew point with a challenge of 21 °C (70 °F) dew point and 100 psig. If the incoming air has an inlet dew point of only 0 °C (32 °F), the outlet dew point will be somewhat less. Pressure also plays a role. If the pressure is higher than the rated specification then the outlet dew point will be lowered. This lowering of the outlet dew point is due to the longer residence time that the air has inside the membrane. Using the spec above, an operating pressure of 120 psig will yield a lower outlet dew point than specified. The extent of the improvement is dependent on the nature of the membrane and could vary among manufacturers.
  Membrane air dryers are designed to operate continuously, 24 hours per day, 7 days per week. Membrane air dryers are quiet, reliable and require no electricity to operate. If set up and operated properly, membrane dryers can produce extremely low dew points.  For this reason they are very common in laboratories, medical facilities and specialty manufacturing environments where limited amounts of high quality compressed air is required.  They are usually set up as a point-of-use dryer and provide the best service when used in a second or third stage role.  The delicate nature of the equipment and how it is used makes them generally unsuitable for more mainstream or industrial applications. Membrane air dryers are used in pneumatic components, spray painting, laser plenum purge, air bearings, air spindles, medical equipment, air guns and pneumatic brakes for vehicles and trains.
caption: Schematic representation of a membrane type compressed air dryer.
exif: {}