Glossary of Terms

Air Consumption:
The volume of compressed air per unit of time required to operate a vacuum pump; measured in standard cubic feet per minute (scfm).

Air Knife:
An extruded or fabricated vessel with a slot designed such that the volume of air in the vessel is greater than that which can escape at atmospheric pressure causing velocity and pressure as a usable work force.

Anodized Aluminum:
Plating of aluminum to prevent rusting and to enhance the strength of aluminum.

Anti-suck back Valve
Typically, a check valve that is built in to the inlet of a vacuum pump and is designed to prevent the migration of oil and air from a vacuum pump in to the system when the vacuum pump stops and the chamber or system is under vacuum. Negates the need for a separate check valve.

Atmospheric Pressure:
The force exerted on a unit area by the weight of the atmosphere. At sea level, atmospheric pressure equals 14.7 psi.

BHP: (Brake Horsepower)
This is the total horsepower required at the input shaft of a vacuum pump at specific pressure. BHP curves can be generated to show the input horsepower over the entire vacuum range the pump can achieve.

BSP: (British Standard Pipe)
A measurement of thread pitch and count.

Backing Pump:
A vacuum pump used to evacuate gases from the discharge of another vacuum pump. Can be used for diffusion pumps, turbo molecular pumps, blowers, etc. Also called a fore pump.

Back Pressure:
Resistance to flow in a system.

Bar:
A measurement of vacuum. Multiply inches of mercury times 0.03386 to obtain bar.

Barometric Pressure:
The reading in inches of mercury (in Hg), showing atmospheric pressure at a given location.

Blast:
Positive pressure air used in the printing industry to separate paper by blowing against the edges to provide lift.

Bernoulli’s Principle:
There is, in general, such a relation between pressure and velocity, that whenever the velocity of a fluid (such as air or water) is high, the pressure is low and vice versa.

Booster Pump:
Typically a Roots type rotary lobed blower. These pumps act as high capacity “boosters” to mechanical backing pumps at specific vacuum ranges. There are also some vapor pumps that are referred to as booster pumps.

Boyles’ Law:
The absolute pressure of a fixed mass of gas varies inversely as the volume, provided the temperature remains constant.

CFM: (Cubic Feet per Minute)
A method of measurement of flow of fluids, like air.

Coalescing:
The process where small aerosols and fine mists are combined into larger droplets that can be removed from an air stream. Final coalescing is usually done with a specific coalescing element after the air stream passes through several baffle stages.

Conductance:
This is the actual capacity of a vacuum piping system in terms of flow. Can be described in ACFM, M3/Hour, Litres/Second, etc. Conductance in a vacuum system can be limited by line size and line configuration.

Cycle Time:
The time it takes to complete one full function, e.g. the evacuation of a mold from atmospheric to the required level of vacuum, then back to atmospheric.

Decibel: (Also dBA)
An exponential measure of sound levels.

Degassing:
Removing gas from a solid or liquid material under vacuum.

Differential Pressure:
It is the difference in pressure between two points in a vacuum or filter system. In filter assemblies, it is usually expressed as the delta P between a housing inlet and outlet.

Evacuation Time:
The time it takes to evacuate a volume to a desired level of vacuum.

Flow Rate:
The volume of fluid or air passing a point per unit of time. In vacuum, the unit volume of air evacuated from or through a given area.

Free Air Capacity:
The volume of air passed per unit time through a vacuum pump when the pressure and exhaust sides is equal to atmospheric pressure. Used as a rating of vacuum pump performance.

Gas Ballast:
A device used to prevent the condensation of vapors in a vacuum pump by admitting a small amount of air into the compression chamber. This device not only prevents the condensation of vapors, it can also help remove condensed vapors in a vacuum pump oil.

Gauge Pressure:
The difference between pressure remaining in an evacuated system and atmospheric pressure. Also know as “gauge vacuum” or “vacuum level”.

ICFM: (Inlet Cubic Feet per Minute)
Air flow at inlet conditions to the inlet of rotary lobed blower or booster vacuum pump. In vacuum applications, it is the same as ACFM.

ISO: (International Standards of Organization)
A system that enforces compliance to established quality standards.

Inches of Mercury:
Two very common scales used to measure vacuum pressures (“HgA and “HgV). The scale ranges from 29.92” Hg to 0” Hg and scale orientation depends on whether it is used as a gauge scale or an absolute scale. One inch of mercury equals 25.4 torr.

Inches of Water:
Units used to measure small pressure differentials across filter components for both vacuum and pressure applications. One inch of water column equals 1.868 torr (or 1 PSI = 27.7” H2O).

Kilowatt:
A measure of electrical consumption. Multiply horsepower by 0.7457 to obtain kilowatts.

L/S: (Litres per Second)
A measurement of flow. Multiply cubic feet per minute by 0.472 to obtain L/S.

Mass Flow:
The weight of a gas or airflow going into a vacuum system. Usually expressed in SCFM or Pounds per Hour and is then converted to volume flow (ACFM) for pump sizing.

Micron Rating:
A measurement of pore size.

Non-Return Valve:
A device that, when placed in an air or vacuum line, prevents the flow from reversing direction.

PSIA: (Pounds per Square Inch Absolute)
Pressure measured from a state with a total absence of air.

PSIG: (Pounds per Square Inch Gauge)
Pressure above or below (vacuum) atmospheric.

Pascal’s Law:
A pressure applied to a confined fluid at rest is transmitted with equal intensity throughout the fluid at right angles to containing surfaces.

Percent Vacuum:
A type of vacuum measurement. (50% vacuum – 15”Hg).

Positive Displacement: (of a compressor or vacuum pump)
One that moves a specific volume of air for each cycle of operation.

Pressure Differential:
Any difference in pressure between two points in a system.

Receiver Tank:
Accommodates sudden surges in demand and eliminates constant cycling on and off of vacuum pumps.

Roughing Pump:
The vacuum pump used to evacuate a high vacuum system to the point where the high vacuum pump can take over.

SCFM: (Standard Cubic Feet per Minute)
The standard for mass flow in vacuum systems at standard conditions: 760 torr, 68 degrees F and 36% RH.

Time of Evacuation:
The time it takes to evacuate a given volume to a desired level of inches Hg.

UL: (Underwriters Laboratories Inc.)
An organization concerned with safety of personnel and property. A UL listing indicates compliance with UL safety standards for mechanical and fire hazards.

Vacuum:
That pressure which is lower than the surrounding atmospheric pressure.

Vacuum Conveying:
Using vacuum force to transport material such as powders, granulates or slurries from one point to the other.

Vacuum Flow:
The rate at which atmospheric air is removed from a system, expressed in scfm.

Vacuum Relief Valve:
A valve that controls mechanical system vacuum level. It operates by providing a modulated flow of atmospheric air into the system.

Volume:
The combination of all area in a vacuum system from the interior of the pump to, and including, the area of application.


The combination of all area in a vacuum system from the interior of the pump to, and including, the area of application.