V/PSA Technology
V/PSA stands for “Vacuum / Pressure Swing Adsorption”. Oxygen is separated from a mixture of gases under pressure using zeolite, after which the saturated zeolite is allowed to regenerate using a vacuum pump. Two alternating vessels are used to ensure continuous flow.
What is Vacuum / Pressure Swing Adsorption?
V/PSA uses ambient air as a source to produce the oxygen needed for medical purposes. Ambient air contains multiple gases: typically 21% oxygen, 78% nitrogen, 0.9% argon and 0.1% rare gases. V/PSA uses pressure and a molecular sieve to separate the oxygen. The resulting product gas is oxygen, argon and a little nitrogen which meets the pharmacopeia requirement for Oxygen 93. It then uses vacuum to regenerate the molecular sieve.
Vacuum / Pressure
V/PSA concentrators typically are comprised of two identical vessels filled with zeolite media. These two vessels are put under pressure (usually a screw type compressor) in an alternating pattern. While one vessel is under pressure, the other uses a vacuum pump.
Swing
The alternating pattern of maximum pressure vs. vacuum (the swing) is needed to ensure a nearly continuous output flow. While one vessel is producing medical-grade oxygen (under pressure), the other allows the zeolite to regenerate (using the vacuum pump).
Adsorption
As the air flows through the vessel, the zeolite holds back the nitrogen molecules, water vapor and pollutants. Only oxygen and argon molecules are allowed to flow through the vessel and out to the system.
How does it work?
Pressure, adsorption and a switch
Air is compressed by an air compressor and passed into one of the two concentrating vessels. As the air flows through, the zeolite acts as a molecular sieve, allowing only oxygen and argon molecules to flow through the vessel and out to the system. Gradually, the nitrogen saturates the zeolite. If nothing were done, the concentration of oxygen would fall off, but before this can happen, the air supply is switched to the second vessel while a vacuum pump is used to create a vacuum in the first vessel. This alternation is controlled by multiple valves and can be on a timed cycle or controlled by instrumentation monitoring saturation of the zeolite in the vessels.
Vacuum, regenerating and ‘the swing’
The vacuum pump pulls the retained nitrogen, water vapor and other gases off the zeolite, clearing out the necessary space in the zeolite matrix for another cycle.
The process relies on the pressure being elevated during the concentration cycle, then switching to a vacuum and back again, hence “vacuum / pressure swing”.
