Page 228 - WaterSense at Work

WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities
Vacuum Pumps
Laboratories, medical facilities, and dental offices use vacuum pumps to collect waste
gases, liquids, or debris from a vessel or enclosure. These vacuum pump systems
range in size, depending upon whether they are used to supply a vacuum to several
rooms or for point of use. Dental offices’ pumps range from 1.0 to 4.0 horsepower
hp), while a central vacuum pump in a medical facility can be 5.0
to 20.0 hp.
Vacuum pumps can use water in two ways: to cool
the pump or to create the vacuum seal in the rotating equipment,
which generates the vacuum.
An aspirator is a type of vacuum system that can consume water
in the process of creating the vacuum. In an aspirator, fluid (e.g.,
liquid, gaseous) flows through a narrowing tube. As the tube
narrows, the velocity of the fluid increases and the static pres-
sure within the system decreases due to the Venturi effect, which
creates a vacuum. The simplest type of aspirator uses water as the
fluid medium, which is used once and discharged to the drain,
making the process very water-intensive. Because of their sim-
plicity, water aspirators might commonly be found in many high
school and college laboratories, but their use can be limited to just
a few hours each semester. Although water aspirators are available,
they are not the focus of this section. Instead, this section focuses
on vacuum pump systems, which are more commonly found in
commercial and institutional facilities. If a facility has a water aspirator that is used
frequently, it should consider the replacement options discussed in this section.
Generating the Vacuum
Vacuum pumps can either be “dry” or “wet”—based upon how the vacuum seal is
generated within the pump. Dry pumps do not use water to generate the seal for the
vacuum. Instead, they create vacuums with turbines (i.e., fans) or use positive dis-
placement (e.g., vane pumps, claw pumps, piston pumps). Wet pumps use a closed
impeller that is sealed with water or other lubricants such as oil to generate the
The most common type of wet vacuum pump is a liquid-ring vacuum pump, which
uses water to form a moving cylindrical ring inside the pump casing. In these pumps,
the vacuum is created by the changing geometry inside the pump casing as the im-
peller and liquid ring rotate. As the vacuum seal water rotates with the pump, it gains
heat and gathers impurities from gases collected by the vacuum system.
In the most simple liquid-ring vacuum pump systems, the seal and cooling water
are continuously discharged and replenished with fresh water to dissipate heat and
East Bay Municipal Utility District (EBMUD). 2008.
WaterSmart Guidebook—A Water-Use Efficiency Plan Review Guide for New Businesses
Page MED2.
Vacuum pumps at the Kansas City
Science and Technology Center