Liquid Ring Vacuum Pumps are limited in the vacuum they can produce.
The vapor pressure of the sealant fluid is the limiting factor and vacuum is usually limited to about 25 torr. Most liquid ring vacuum pumps operate between 50-75 torr. When deeper vacuum is required, an Atmospheric Air Ejector may be used as an extra pumping stage. The Atmospheric Air Ejector (AAE) is installed in the suction and can pull the vacuum down to 5-10 torr. The AAE sucks in atmospheric air and discharges it into the pump suction.
The Atmospheric Air Ejector converts the pressure energy of atmospheric air (at high pressure relative to the vacuum pump) and converts it into kinetic energy. The deeper vacuum is produced at this point, and the kinetic energy is reconverted to pressure energy in the diffuser, or matches the suction pressure of the pump. The method of operation would be to turn on the pump first, then after the pump vacuum is reached, the air valve can be opened.
A common application for the AAE is a tow-stage cold water degasifier.
Tow parallel atmospheric air ejectors, one operating at 20-25 torr and the other operating at 10-15 torr, maintain different vacuum in the two different compartments of the degasifier. They both discharge to the same pressure, usually 60-75 torr. The two discharge are manifolded together and sent to the same liquid ring vacuum pump or bank of parallel pumps.
When specifying an Atmospheric Air Ejector, the following must be noted
SUCTION AT VACUUM PUMP INLET (TORR)