Glossary
absolute pressure
The total pressure measured with reference to absolute zero pressure, that is, the condition of perfect vacuum. The following values correspond to absolute zero pressure: 0 Pa = 0 Torr = 0 mbar.
absolute zero
The temperature at which gas-phase molecules have zero kinetic energy. This value is known as zero degrees Kelvin (0 K) which is approximately -273.15 oC.
absorption (absorb)
The taking up of a gas or vapor by a solid or liquid due to physical forces in which the gas diffuses into the bulk of the solid or liquid.
adsorption (adsorb)
The taking up of a gas or vapor by a solid or liquid due to physical forces in which the gas is retained at the surface of the solid or the liquid. Adsorbed gases are not bound to a surface permanently.
atmospheric pressure
The pressure exerted typically by the Earth’s atmosphere. Also see standard atmospheric pressure and standard temperature and pressure (STP).
Avogadro’s number
The number of molecules of an ideal gas that would be contained in 22.4 liters at standard atmospheric pressure and temperature (1 atm, 0 oC). This quantity is about 6 x 1023.
backing pump
See pump, backing.
backstreaming (oil)
When unwanted gases like oil vapor or particles flow from downstream pumping or other components toward the vacuum chamber or process components, that is, in a direction opposite to the direction of the desired gas flow.
bar and millibar
The bar is a metric unit of pressure but is not part of the International System of Units (SI). One bar is exactly equal to 100,000 Pa. The millibar (mbar) is a unit of pressure typically used to express vacuum pressures. One mbar is exactly equal to 100 Pa.
Bayard Alpert (hot cathode) ion gauge
See gauge, Bayard Alpert (hot cathode) ion.
Bourdon gauge
See gauge, Bourdon.
Boyle's law
Gas law that states that if the temperature and the amount of gas are held constant, the volume of gas is inversely proportional to the pressure exerted by the gas.
bulk gas
The volume of gas trapped within the chamber and vacuum piping components prior to initiating a pump-down cycle. Also called volume gas.
butterfly valve
A type of high-vacuum valve with a movable circular plate that is mechanically adjusted to allow varying levels of gas flow through the valve’s orifice or block gas flow altogether.
capacitance diaphragm gauge
See gauge, capacitance diaphragm.
capture pumps
See pumps, capture.
conflat-type (CF) flange
A type of de-mountable metal-sealed joint used in vacuum technology that supports ultra-high vacuum operation. Also known as conflat-type (CF) fitting.
chamber
The sealed part(s) of pressure-controlled research or production apparatus where vacuum and/or other processes occur.
Charles's law
Gas law that states that the volume of a gas is directly proportional to the absolute temperature at a constant pressure. Also known as the law of volumes.
compressibility
A measure of the instantaneous relative volume change of a fluid or solid as a response to a pressure change.
condensation
Generally referring to the condition when gas-phase molecules have adsorbed onto a surface or coalesced within a volume to an extent that this can be visually observed.
conductance
A parameter used to represent the ease of a molecule’s flow through an obstacle based on the pressure difference on either side of the obstacle.
convection-enhanced Pirani (thermal) gauge
See gauge, convection-enhanced Pirani (thermal).
cryogenic (cryo) pump
See pump, cryogenic (cryo).
Dalton’s law
The total pressure is equal to the sum of the partial pressures of each gas in the mixture.
degassing
The deliberate desorption of gas from a material.
desorption (desorb)
The liberation of gases and vapors sorbed (adsorbed and absorbed) by a material.
diaphragm gauge
See gauge, diaphragm.
diaphragm pump
See pump, diaphragm.
diffusion
A process in which atoms or molecules move through a solid, liquid or gas.
diffusion pump
See pump, diffusion.
direct reading (pressure) gauges (manometers)
See gauges, direct reading (pressure) gauges (manometers).
dry pumps
See pumps, dry.
effective pumping speed
The pumping speed that a vacuum pump can provide when it is limited by conductance of a tube and/or an orifice.
elastomer
A natural or synthetic polymeric material that demonstrates elastic properties.
equilibrium vapor pressure
The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
evaporation
A process where surface-bound molecules are thermally desorbed from a solid or liquid surface to become part of the gas phase. Evaporation typically takes place below the boiling temperature.
exhaust line
A tube that connects the gas outlet from a vacuum system to a building exhaust system.
feedthrough
A vacuum component that transfers motion, electrical charge, water, light, heat, etc. into and/or out of a vacuum chamber while maintaining vacuum.
fluid sealed vacuum pump (wet pump)
See pumps, wet.
foreline
The vacuum tube that connects the output of a high-vacuum diffusion, turbomolecular, and/or drag pump to a rough-vacuum mechanical backing pump.
freeze, freezing
The transition of a liquid to a solid by the removal of heat, i.e. lowering the temperature of the liquid. An example is water, a liquid at room temperature, when it turns to ice as the temperature is lowered below its freezing point.
gage pressure
The difference between absolute pressure and atmospheric pressure.
gas ballast pump
See pump, gas ballast.
gas load
The amount of gas that must be removed from the chamber in a vacuum system by the vacuum pump(s). It is typically measured in torr-liters per second, cubic feet per minute, or cubic meters per hour.
gas molecule
An individual particle in a vacuum that has neither a defined volume or shape. A gas molecule can be a single atom (e.g., a noble gas such as Argon, Ar) or a number of atoms bonded together to form a compound (e.g., such as water, H2O).
gas phase
A structural state of matter in which the thermal motion of the respective molecule species near room temperature is sufficient to exceed any cohesive forces, and permit their free motion. Contrast with term vapor phase.
gas transfer pumps
See pumps, gas transfer.
gate valve
A large diameter valve usually placed between the vacuum chamber and the vacuum pumps to isolate the vacuum chamber from the pumps when it is necessary to work on something in the chamber.
gauge, Bayard-Alpert (hot cathode) ion
A type of indirect reading vacuum gauge in which a heated filament supplies free electrons at a constant controlled rate due to thermionic emission. The number of resulting ions collected in this gauge type is an indication of the total pressure present. The Bayard Alpert ion gauge is the most typical hot-filament ion gauge used.
gauge, Bourdon
A type of direct reading vacuum gauge with a thin-walled metal tube bent into a circular arc that will straighten if pressure is applied to the inside of the tube. The movement of the metal tube is used to indicate pressure. Bourdon gauge was invented by Eugene Bourdon (1808-1884), a brilliant French watchmaker and engineer, in 1849.
gauge, capacitance diaphragm
A type of direct reading vacuum gauge where a measurement of electrical capacitance of the diaphragm position is used to indicate pressure. Also known as capacitive gauge.
gauge, convection-enhanced Pirani (thermal)
A Pirani gauge that incorporates a secondary heated wire, a compensator, which surrounds the primary heated sensor wire. Incorporating the resistance of the compensator wire serves to counteract temperature variations of the gauge body. A convection-enhanced Pirani gauge measures pressures up to atmospheric pressure and thus has a wider pressure measurement range than a basic Pirani gauge.
gauge, diaphragm
A manometer-type and direct reading rough vacuum gauge that measures the displacement of a thin solid membrane caused by pressure difference on opposite sides of the membrane.
gauge, hot-cathode ionization
An ionization vacuum gauge in which the gas is ionized by electrons emitted from a heated cathode. Also see ionization vacuum gauges (gauges, ionization). Also can be called hot-filament ionization gauge or hot-filament gauge.
gauge, McLeod
A type of direct reading vacuum gauge which is used to measure very low pressures, down to 10−6 Torr (1.33 mPa). It was invented in 1874 by Herbert McLeod.
gauge, MEMS Pirani
A MEMS Pirani vacuum sensor, gauge or transducer is a device for measuring vacuum gas pressure by measurement of the pressure dependent heat-loss from a heated resistive element deposited on a suspended micro-machined diaphragm. The MEMS Pirani vacuum transducer can measure vacuum gas pressure over a span of 9 decades from atmospheric pressure down to 7.5 x 10-7 Torr).
gauge, piezo-resistive (vacuum)
Piezoelectricity is the charge created across certain materials when a mechanical stress is applied. Piezoelectric pressure sensors exploit this effect by measuring the voltage across a piezoelectric element generated by the applied pressure. They are very robust and are used in a wide range of industrial applications.
gauge, piezoelectric (vacuum)
See gauge, piezo-resistive (vacuum).
gauge, Pirani
A thermal conductivity pressure gauge containing a heated filament having a large temperature coefficient of resistance as an element of a resistive bridge. Because heat dissipation from the filament is a function of the gas pressure in a certain pressure range, filament resistance or power required to maintain a constant filament resistance can be correlated with gas pressure. Invented by German Physicist, Marcello Pirani (1880-1968) in 1906.
gauge, thermocouple
A specific type of thermal vacuum gauge where the temperature of the wire sensor is measured with a thermocouple to estimate pressure within the gauge.
gauges, direct reading (pressure) gauges (manometers)
Pressure gauges that operate by sensing deflection of a solid or liquid surface caused by momentum transfer to that surface from energetic gas molecules. Direct reading gauges are largely insensitive to gas type.
gauges, indirect reading (pressure)
Pressure gauges that measure a property related to gas pressure and then convert that measurement into a gas pressure reading.
gauges, ionization vacuum
Vacuum gauges in which the molecular density is determined by measuring the ion current produced in the gas by ionization under controlled conditions. The ion current is directly related to gas density, and hence, is proportional to the gas pressure.
gauges, pressure
See gauges, vacuum (pressure).
gauges, thermal (conductivity)
Any one of several vacuum gauges where the temperature of an internal heated wire sensor is measured to estimate pressure.
gauges, vacuum (pressure)
One of several types of electrical or mechanical devices used to measure pressure and/or gas density at various locations of a vacuum system.
Gay-Lussac’s law
Gas law that describes how the absolute pressure of a gas depends on its temperature while the volume of the gas is held constant. Also known as Amonton’s law.
hot-cathode ionization gauge
See gauge, hot-cathode ionization.
house exhaust system
A centralized system within a building to remove exhaust gases from pumps and pumping systems.
hydrogen bond
Molecules that have a hydrogen bonded to nitrogen, oxygen, or fluorine have unusually strong dipole-dipole attractions called hydrogen bonds.
ideal gas constant
The proportionality constant (R) used in the Ideal Gas Law that relates the product of gas pressure (P) in a give volume (V) to the gas temperature (T) and number of molecules (n) present in the volume (i.e., PV = nRT). For P in Torr, V in Liters, and T in Kelvin, the gas constant is approximately 1 x 10-22 Torr-Liter /(Molecule-Kelvin).
indirect reading (pressure) gauges
See gauges, indirect reading (pressure).
ionization vacuum gauges
See gauges, ionization vacuum.
ISO flange
A high vacuum flange that uses a metal O-ring to seal the connection between two components using either clamps or bolts.
isolation valve
A valve placed between two components, or parts of a vacuum system, that blocks the flow of gas between the two parts.
KF (Klein Flansche) flange
Quick-release flange couplings in sizes DN 16 to DN 40, suitable for low (rough), medium and high vacuum. Elastomer gaskets and metal gaskets can alternatively be used for sealing. KF (Klein Flansche) flange is also known as KF (Klein Flansche fitting).
kinetic vacuum pumps
See pumps, kinetic vacuum.
Knudsen number
The ratio of the mean-free path of a molecule in a vacuum environment to a characteristic size of that particular vacuum environment.
laminar flow
A type of viscous gas flow where particles travel smoothly in regular paths, and the particle velocity is generally much slower near stationary objects in the flow path. No turbulent mixing occurs in viscous gas flow.
leaks, gross (real)
A crack, hole, or other pathway that allows gases to pass through from outside the vacuum system to inside the vacuum system. Also known as gross leaks.
leaks, virtual
A volume of trapped gas that enters the vacuum system when the system is pumped down.
lobe blower pump
See pump, Roots (blower).
mBar
See bar and millibar.
McLeod gauge
See gauge, McLeod.
mean free path (MFP)
The average distance which a molecule travels between two successive collisions with other molecules of the gas.
mechanical pumps, mechanical roughing pumps
See pumps, mechanical (roughing).
MEMS Pirani gauge
See gauge, MEMS Pirani.
molecular density
The number of molecules per unit volume of gas.
molecular flow
Gas flow in which molecules interact primarily with surfaces in or along the flow path rather than with other molecules. Contrast with viscous flow.
momentum transfer pump
See pumps, momentum transfer.
net pumping speed
The mean volume flow through the cross section of the inlet port of a vacuum pump after the effect of all conductances have been accounted for.
O-ring
A mechanical gasket in a circular shape made of an elastomer with a round cross section or metal such as copper. O-ring is sandwiched between two components and blocks a path which may otherwise allow gas to escape. Essentially, they help to prevents leaks when two components are joined together.
outgassing
The process of gas molecules that are weakly bound to a surface, bound to pores or cracks in a material, or diffused into the bulk leaving the surface to become gas-phase molecules. Also known as surface desorption.
partial pressure
The pressure exerted by a particular species of gas molecules. According to Dalton’s law, the sum of the partial pressures of all the component species in a mixture is equal to the total pressure.
pascal (Pa) and kilo-pascal (kPa)
The SI unit of pressure equal to one newton per square meter. There are 101,325 pascals in one standard atmosphere. There are 1,000 Pa in 1 kPa. Named after French mathematician and philosopher, Blaise Pascal (1623-1662).
permeation (permeability)
The process of molecular penetration of gases, vapors, or fluids completely through a material.
piezo-resistive gauge
See gauge, piezo-resistive (vacuum).
piezoelectric vacuum gauge
See gauge, piezo-resistive (vacuum).
piezoelectricity
The ability of certain materials to change resistance or generate an electric charge in response to applied mechanical stress, and vice versa.
Pirani gauge
See gauge, Pirani.
piston (vacuum) pump
See pump, piston (vacuum).
poppet valve
A valve typically used to control the timing and quantity of gas flow.
positive displacement pump
See pumps, positive displacement.
pressure
A way of measuring how much force is acting over an area or the perpendicular force per unit area.
pressure gauges
See gauges, vacuum (pressure).
psi (psig)
A pressure unit defined as Pounds per Square Inch (of Gas).
pump, backing
A rough vacuum pump used in a vacuum system with the inlet of the rough vacuum pump connected to the outlet of a momentum transfer type-high vacuum pump. The rough vacuum pump operates to maintain an effective pressure in the foreline (also called backing line) for the expected throughput.
pump, claw
Claw pumps use two claws rotating in opposite directions, like the Roots pump, to capture, compress, and exhaust the gas. Claw pumps can be used to effectively pump corrosive and abrasive gases. They are often combined with Roots pumps to achieve high pumping speeds and pressures in the millitorr range.
pump, cryogenic (cryo)
A type of high vacuum pump that uses cold surfaces to remove gas-phase molecules by cryocondensation and/or cryosorption. Often used to refer to a vacuum pump operated with closed-cycle helium refrigeration system. Cryopump technology is based on Gifford-McMahon cryocooler which was first used to make a vacuum pump by Helix Technology Corporation in 1976.
pump, diaphragm
A type of dry mechanical, rough vacuum pump that utilizes a movable diaphragm element to displace and compress a volume of gas from an inlet to an outlet region.
pump, diffusion
A high vacuum pump that uses a directed stream of heavy vapor molecules to flow gas molecules toward increasing higher pressure regions in the pump. Diffusion pump was invented in 1915 by Wolfgang Gaede.
pump, gas ballast
A positive-displacement pump in which a controlled quantity of a suitable non-condensable gas is admitted during the compression part of the cycle so as to reduce the extent of condensation within the pump. This technology was originally developed by Wolfgang Gaede in 1935.
pump, lobe blower
See pump, Roots (blower).
pump, piston (vacuum)
A type of positive displacement pump where the high-pressure seal reciprocates with the piston. Also called rotary piston (vacuum) pump.
pump, reciprocating (vacuum)
A vacuum pump that draws air by periodically changing the working volume of the pump.
pump, Roots (blower)
A rotary plunger type pump where two symmetrically shaped impellors rotate in opposite directions inside the pump housing. Roots pumps are used where great volumes have to be pumped. Also known as lobe blower pump.
pump, rotary vane
A positive-displacement pump that consists of vanes mounted to a rotor that rotates inside a cavity. Invented by Charles C. Barnes in 1874.
pump, screw
A dry mechanical pump that contains two screw rotors which rotate inside a cylinder. The gas is trapped between cylinder and screw chambers and carried to the gas exhaust.
pump, scroll
A dry mechanical vacuum pump design that utilizes two intermeshed spirals (i.e., scrolls) to displace and compress a crescent-shaped volume of gas from an inlet to an outlet region.
pump, vacuum
A vacuum component that moves gas molecules from a low-pressure region to a higher-pressure region. Vacuum-pump design is typically specific to its operating-pressure region, with the three main pressure regions being low vacuum (i.e., atmospheric pressure to ~10-3 Torr), high vacuum (i.e., 10-3-10-9 Torr), and ultra-high vacuum (i.e., less than 10-9 Torr).
pumps, capture
A classification for high vacuum pumps that operate by adsorbing gas-phase molecules onto a surface or into a bulk material.
pumps, dry
Vacuum pumps that use no fluids for sealing or momentum transfer.
pumps, gas transfer
Vacuum pumps that remove gas from the vacuum chamber, move it through the pump, and then exhaust the gas to the building exhaust system or into the environment.
pumps, kinetic vacuum
Kinetic vacuum pumps use various mechanisms to transfer momentum to gas molecules in order to move them toward the outlet port of the pump. Diffusion pumps use oil jets to impart momentum to gas molecules while turbomolecular pumps use high-speed turbine blades.
pumps, mechanical (roughing)
In vacuum systems, mechanical pumps are motor-driven pumps that move gas from the inlet port to outlet port using a mechanical mechanism, e.g. rotary vanes, scrolls, pistons, and diaphragms among others.
pumps, momentum transfer
A classification of pump where one part of the pump (either a solid component or molecular vapor) imparts preferred momentum to gas-phase molecules.
pumps, positive displacement
A classification of pump that captures a volume of gas near the inlet and mechanically displaces it to the outlet. Often compression of the captured volume occurs between the inlet and the outlet.
pumps, rotary (vacuum)
Mechanical pump that utilizes rotary motion to drive pumping mechanism. Examples of rotary pumps are screw pump, lobe blower pump, and rotary vane pump.
pumps, rough (vacuum)
See pumps, mechanical (roughing).
pumps, roughing (vacuum)
See pumps, mechanical (roughing).
pumps, wet
A vacuum pump that uses a fluid or vapor for sealing or momentum-transfer. Also known as fluid sealed vacuum pump.
pump down
Commonly used term for evacuation of a vacuum chamber from atmospheric pressure to a pre-defined base pressure.
pump-down curve
Graph describing a time-dependent pressure drop in a vacuum system; popular control instrument when designing and operating a vacuum system.
pump-down time
Time required to evacuate a chamber from atmospheric to a predefined base pressure.
pumping speed
The volume of gas that will flow past a given plane in a gas flow path in a given amount of time. Units are in volume per time (e.g., Liters per second). See also Volumetric Flow Rate.
pumping speed curve
A graphical representation of the pumping speed performance of a pump as a function of the pressure of the gas being pumped.
rarefaction
Decrease in density of gas.
real leak
See leaks, gross (real).
reciprocating (vacuum) pump
See pump, reciprocating (vacuum).
retard
Delay in time.
Roots (blower) pump
See pump, Roots (blower).
rotary piston (vacuum) pump
See pump, piston (vacuum).
rotary (vacuum) pump
See pumps, rotary (vacuum).
rotary vane pump
See pump, rotary vane.
rough (vacuum) pump
See pumps, mechanical (roughing).
rough vacuum (pressure) regime
Vacuum pressure regime with pressures between 760 Torr and 1 X 10-3 Torr.
roughing, roughing line
Roughing a vacuum chamber indicates that it is being evacuated with a low-vacuum pump through a roughing line from atmospheric pressure to a pressure that is sufficiently low to allow a high vacuum pump to be engaged.
roughing pump
See pumps, mechanical (roughing).
saturation
The state or process that occurs when no more of something can be absorbed, combined with, or added.
saturation vapor pressure
The pressure exerted by a vapor which is in thermodynamic equilibrium with one of its condensed phases at the prevailing temperature.
screw pump
See pump, screw.
scroll pump
See pump, scroll.
series conductance
When various vacuum components, each with different values of conductance, are arranged in a single flow path, therefore requiring each gas molecule to transit through each vacuum component.
SI
International System of Units (Abbreviation of French: Systeme International d’unites). The only system of measurement with official status in nearly every country in the world.
standard atmospheric pressure
Pressure defined in 1925 by the National Advisory Committee for Aeronautics as 760 Torr (101,325 Pascal, or 1013.25 mBar, or 29.9213 inches of Hg) for a “normal” day at 0°C and at sea level.
standard temperature and pressure (STP)
In vacuum technology, defined as a temperature of 273 K (0º C, 32º F) and an absolute pressure of exactly one standard atmosphere (1 atm, 760 Torr, or 101.325 kPa at sea level). Since 1982, Defined by IUPAC (International Union of Pure and Applied Chemistry) as a temperature of 273 K (0º C, 32ºF) and an absolute pressure of exactly 105 Pa (100 kPa, 1 bar).
sublimation
Transition of a substance directly from a solid state/phase to a gas state/phase.
surface outgassing
The release of surface-bound molecules to the gas phase. For most vacuum systems, the main species of surface-bound molecule is water. Measured as a mass flow rate (e.g., in Torr-Liters/sec).
thermal (conductivity) gauges
See gauges, thermal (conductivity).
thermocouple gauge
See gauge, thermocouple.
throttle valve (throttling valve)
A vacuum valve that can be controlled by the operator to be only partially open (or partially closed). Allows to control pumping speed by decreasing conductance (to throttle) between a vacuum chamber and a vacuum pump.
throughput
Term used to indicate molecular flow rate or mass flow rate. Identifies number of molecules flowing past a plane in a flow path. Units are in Pressure x Volume / Time (e.g., Torr-Liter/Sec).
torr
Widely used (but non-SI) pressure unit in vacuum technology, equal to 1 mm of mercury in a historic barometer, and named after Italian physicist Evangelista Torricelli (1608-1647). Torr is still widely used in the US, and is therefore the pressure unit primarily used in this e-book.
ultimate pressure
Lowest attainable pressure in a vacuum system. In a vacuum pump, the lowest pressure that can be attained with that pump. Ultimate pressure is limited by the pumping speed of the vacuum pump and the vapor pressure of the sealing fluid, among other factors.
universal gas constant
See ideal gas constant.
vacuum
A “prefect vacuum” is defined as a space that is entirely devoid of any gas molecules. However, in vacuum technology, the more useful definition is a space in which the density of gas molecules is significantly reduced below that of atmospheric pressure, or where the mean-free-path is sufficient to conduct the desired vacuum process.
vacuum chamber
See chamber.
vacuum component
Any one of the many parts that are required to construct a functioning vacuum system, or parts required to undertake and control a vacuum process.
vacuum fluid
Generally, an organic or inorganic fluid that has a sufficiently low vapor pressure, as well as chemical and thermal stability to enable effective use as a lubricant and/or sealant in certain vacuum systems or processes.
vacuum (pressure) gauges
See gauges, vacuum (pressure).
vacuum grease
A two-part mixture comprised of vacuum-fluid molecules (i.e., base gel) and much larger molecules or particles (i.e., thickener). The components of the mixture are selected to demonstrate desirable mechanical, thermal, and other properties, and also demonstrate sufficiently low vapor pressure to allow its use as a lubricant and/or sealant in a certain vacuum systems or processes.
vacuum piping components
Vacuum piping components provide pathway for the gas to flow within a vacuum system. Examples of vacuum piping components are tees, nipples, elbows, crosses, reducers, and flanges or fittings.
vacuum pump
See pump, vacuum.
vacuum technology
A body of knowledge and related skills required to undertake processes and measurements under conditions of sub-atmospheric pressure.
vapor, vapor state
The term “vapor” is often used when a material may be present in several phases within a vacuum chamber at a given pressure. For example, during thermal evaporation of a metal, metal generally exists as a solid source, then as a pool of liquid metal as the temperature increases, and finally as a metal vapor evaporating from the surface of the liquid. The evaporated metal vapor will re-condense into a solid when it adsorbs onto any relatively cool surface (i.e., a substrate).
vaporization
Conversion of a substance from the liquid state/phase to the gas (vapor) state/phase.
vent valve
Part of a vacuum system that controls the flow of outside air (or gas) into the vacuum chamber.
virtual leak
See leaks, virtual.
viscous flow
Gas flow in which molecules interact primarily with other molecules, rather than with surfaces in or along the flow path. Contrast with molecular flow.
volume flow rate (volumetric flow rate)
The volume of gas that will flow past a given plane in a gas flow path in a given amount of time. Units are in volume per time (e.g., Liters per second). See also pumping speed.
The total pressure measured with reference to absolute zero pressure, that is, the condition of perfect vacuum. The following values correspond to absolute zero pressure: 0 Pa = 0 Torr = 0 mbar.
The temperature at which gas-phase molecules have zero kinetic energy. This value is known as zero degrees Kelvin (0 K) which is approximately -273.15 degrees Celsius.
The taking up of a gas or vapor by a solid or liquid due to physical forces in which the gas diffuses into the bulk of the solid or liquid.
The taking up of a gas or vapor by a solid or liquid due to physical forces in which the gas is retained at the surface of the solid or the liquid. Adsorbed gases are not bound to a surface permanently.
The pressure exerted typically by the Earth’s atmosphere. Also see standard atmospheric pressure and standard temperature and pressure (STP).
Pressure defined in 1925 by the National Advisory Committee for Aeronautics as 760 Torr (101,325 Pascal, or 1013.25 mBar, or 29.9213 inches of Hg) for a “normal” day at 0°C and at sea level.
In vacuum technology, defined as a temperature of 273 K (0 degree C) and an absolute pressure of exactly one standard atmosphere (1 atm, 760 Torr, or 101.325 kPa at sea level). Since 1982, Defined by IUPAC (International Union of Pure and Applied Chemistry) as a temperature of 273 K (0 degree Celsius) and an absolute pressure of exactly 105 Pa (100 kPa, 1 bar).
The number of molecules of an ideal gas that would be contained in 22.4 liters at standard atmospheric pressure and temperature (1 atm, 0 degrees Celsius). This quantity is about 6E23.
See pump, backing.
A rough vacuum pump used in a vacuum system with the inlet of the rough vacuum pump connected to the outlet of a momentum transfer type-high vacuum pump. The rough vacuum pump operates to maintain an effective pressure in the foreline (also called backing line) for the expected throughput.
When unwanted gases like oil vapor or particles flow from downstream pumping or other components toward the vacuum chamber or process components, that is, in a direction opposite to the direction of the desired gas flow.
The bar is a metric unit of pressure but is not part of the International System of Units (SI). One bar is exactly equal to 100,000 Pa. The millibar (mbar) is a unit of pressure typically used to express vacuum pressures. One mbar is exactly equal to 100 Pa.
See gauge, Bayard Alpert (hot cathode) ion.
A type of indirect reading vacuum gauge in which a heated filament supplies free electrons at a constant controlled rate due to thermionic emission. The number of resulting ions collected in this gauge type is an indication of the total pressure present. The Bayard Alpert ion gauge is the most typical hot-filament ion gauge used.
See gauge, Bourdon.
A type of direct reading vacuum gauge with a thin-walled metal tube bent into a circular arc that will straighten if pressure is applied to the inside of the tube. The movement of the metal tube is used to indicate pressure. Bourdon gauge was invented by Eugene Bourdon (1808-1884), a brilliant French watchmaker and engineer, in 1849.
Gas law that states that if the temperature and the amount of gas are held constant, the volume of gas is inversely proportional to the pressure exerted by the gas.
The volume of gas trapped within the chamber and vacuum piping components prior to initiating a pump-down cycle. Also called volume gas.
A type of high-vacuum valve with a movable circular plate that is mechanically adjusted to allow varying levels of gas flow through the valve’s orifice or block gas flow altogether.
See gauge, capacitance diaphragm.
A type of direct reading vacuum gauge where a measurement of electrical capacitance of the diaphragm position is used to indicate pressure. Also known as capacitive gauge.
See pumps, capture.
A classification for high vacuum pumps that operate by adsorbing gas-phase molecules onto a surface or into a bulk material.
A type of de-mountable metal-sealed joint used in vacuum technology that supports ultra-high vacuum operation. Also known as conflat-type (CF) fitting.
The sealed part(s) of pressure-controlled research or production apparatus where vacuum and/or other processes occur.
Gas law that states that the volume of a gas is directly proportional to the absolute temperature at a constant pressure. Also known as the law of volumes.
A measure of the instantaneous relative volume change of a fluid or solid as a response to a pressure change.
Generally referring to the condition when gas-phase molecules have adsorbed onto a surface or coalesced within a volume to an extent that this can be visually observed.
A parameter used to represent the ease of a molecule’s flow through an obstacle based on the pressure difference on either side of the obstacle.
See gauge, convection-enhanced Pirani (thermal).
A Pirani gauge that incorporates a secondary heated wire, a compensator, which surrounds the primary heated sensor wire. Incorporating the resistance of the compensator wire serves to counteract temperature variations of the gauge body. A convection-enhanced Pirani gauge measures pressures up to atmospheric pressure and thus has a wider pressure measurement range than a basic Pirani gauge.
See pump, cryogenic (cryo).
A type of high vacuum pump that uses cold surfaces to remove gas-phase molecules by cryocondensation and/or cryosorption. Often used to refer to a vacuum pump operated with closed-cycle helium refrigeration system. Cryopump technology is based on Gifford-McMahon cryocooler which was first used to make a vacuum pump by Helix Technology Corporation in 1976.
The total pressure is equal to the sum of the partial pressures of each gas in the mixture.
The deliberate desorption of gas from a material.
The liberation of gases and vapors sorbed (adsorbed and absorbed) by a material.
See gauge, diaphragm.
A manometer-type and direct reading rough vacuum gauge that measures the displacement of a thin solid membrane caused by pressure difference on opposite sides of the membrane.
See pump, diaphragm.
A type of dry mechanical, rough vacuum pump that utilizes a movable diaphragm element to displace and compress a volume of gas from an inlet to an outlet region.
A process in which atoms or molecules move through a solid, liquid or gas.
See pump, diffusion.
A high vacuum pump that uses a directed stream of heavy vapor molecules to flow gas molecules toward increasing higher pressure regions in the pump. Diffusion pump was invented in 1915 by Wolfgang Gaede.
See gauges, direct reading (pressure) gauges (manometers).
Pressure gauges that operate by sensing deflection of a solid or liquid surface caused by momentum transfer to that surface from energetic gas molecules. Direct reading gauges are largely insensitive to gas type.
See pumps, dry.
Vacuum pumps that use no fluids for sealing or momentum transfer.
The pumping speed that a vacuum pump can provide when it is limited by conductance of a tube and/or an orifice.
A natural or synthetic polymeric material that demonstrates elastic properties.
The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
A process where surface-bound molecules are thermally desorbed from a solid or liquid surface to become part of the gas phase. Evaporation typically takes place below the boiling temperature.
A tube that connects the gas outlet from a vacuum system to a building exhaust system.
A vacuum component that transfers motion, electrical charge, water, light, heat, etc. into and/or out of a vacuum chamber while maintaining vacuum.
See pumps, wet.
A vacuum pump that uses a fluid or vapor for sealing or momentum-transfer. Also known as fluid sealed vacuum pump.
The vacuum tube that connects the output of a high-vacuum diffusion, turbomolecular, and/or drag pump to a rough-vacuum mechanical backing pump.
The transition of a liquid to a solid by the removal of heat, i.e. lowering the temperature of the liquid. An example is water, a liquid at room temperature, when it turns to ice as the temperature is lowered below its freezing point.
The difference between absolute pressure and atmospheric pressure.
See pump, gas ballast.
A positive-displacement pump in which a controlled quantity of a suitable non-condensable gas is admitted during the compression part of the cycle so as to reduce the extent of condensation within the pump. This technology was originally developed by Wolfgang Gaede in 1935.
The amount of gas that must be removed from the chamber in a vacuum system by the vacuum pump(s). It is typically measured in torr-liters per second, cubic feet per minute, or cubic meters per hour.
An individual particle in a vacuum that has neither a defined volume or shape. A gas molecule can be a single atom (e.g., a noble gas such as Argon, Ar) or a number of atoms bonded together to form a compound (e.g., such as water).
A structural state of matter in which the thermal motion of the respective molecule species near room temperature is sufficient to exceed any cohesive forces, and permit their free motion. Contrast with term vapor phase.
See pumps, gas transfer.
Vacuum pumps that remove gas from the vacuum chamber, move it through the pump, and then exhaust the gas to the building exhaust system or into the environment.
A large diameter valve usually placed between the vacuum chamber and the vacuum pumps to isolate the vacuum chamber from the pumps when it is necessary to work on something in the chamber.
An ionization vacuum gauge in which the gas is ionized by electrons emitted from a heated cathode. Also see ionization vacuum gauges (gauges, ionization). Also can be called hot-filament ionization gauge or hot-filament gauge.
A type of direct reading vacuum gauge which is used to measure very low pressures, down to 1E−6 Torr (1.33 mPa). It was invented in 1874 by Herbert McLeod.
A MEMS Pirani vacuum sensor, gauge or transducer is a device for measuring vacuum gas pressure by measurement of the pressure dependent heat-loss from a heated resistive element deposited on a suspended micro-machined diaphragm. The MEMS Pirani vacuum transducer can measure vacuum gas pressure over a span of 9 decades from atmospheric pressure down to 7.5E-7 Torr).
Piezoelectricity is the charge created across certain materials when a mechanical stress is applied. Piezoelectric pressure sensors exploit this effect by measuring the voltage across a piezoelectric element generated by the applied pressure. They are very robust and are used in a wide range of industrial applications.
See gauge, piezo-resistive (vacuum).
A thermal conductivity pressure gauge containing a heated filament having a large temperature coefficient of resistance as an element of a resistive bridge. Because heat dissipation from the filament is a function of the gas pressure in a certain pressure range, filament resistance or power required to maintain a constant filament resistance can be correlated with gas pressure. Invented by German Physicist, Marcello Pirani (1880-1968) in 1906.
A specific type of thermal vacuum gauge where the temperature of the wire sensor is measured with a thermocouple to estimate pressure within the gauge.
Pressure gauges that measure a property related to gas pressure and then convert that measurement into a gas pressure reading.
Vacuum gauges in which the molecular density is determined by measuring the ion current produced in the gas by ionization under controlled conditions. The ion current is directly related to gas density, and hence, is proportional to the gas pressure.
See gauges, vacuum (pressure).
One of several types of electrical or mechanical devices used to measure pressure and/or gas density at various locations of a vacuum system.
Any one of several vacuum gauges where the temperature of an internal heated wire sensor is measured to estimate pressure.
Gas law that describes how the absolute pressure of a gas depends on its temperature while the volume of the gas is held constant. Also known as Amonton’s law.
See gauge, hot-cathode ionization.
A centralized system within a building to remove exhaust gases from pumps and pumping systems.
Molecules that have a hydrogen bonded to nitrogen, oxygen, or fluorine have unusually strong dipole-dipole attractions called hydrogen bonds.
The proportionality constant (R) used in the Ideal Gas Law that relates the product of gas pressure (P) in a give volume (V) to the gas temperature (T) and number of molecules (n) present in the volume (i.e., PV = nRT). For P in Torr, V in Liters, and T in Kelvin, the gas constant is approximately 1E-22 Torr-Liter /(Molecule-Kelvin).
See gauges, indirect reading (pressure).
See gauges, ionization vacuum.
A high vacuum flange that uses a metal O-ring to seal the connection between two components using either clamps or bolts.
A valve placed between two components, or parts of a vacuum system, that blocks the flow of gas between the two parts.
Quick-release flange couplings in sizes DN 16 to DN 40, suitable for low (rough), medium and high vacuum. Elastomer gaskets and metal gaskets can alternatively be used for sealing. KF (Klein Flansche) flange is also known as KF (Klein Flansche fitting).
See pumps, kinetic (vacuum).
Kinetic vacuum pumps use various mechanisms to transfer momentum to gas molecules in order to move them toward the outlet port of the pump. Diffusion pumps use oil jets to impart momentum to gas molecules while turbomolecular pumps use high-speed turbine blades.
The ratio of the mean-free path of a molecule in a vacuum environment to a characteristic size of that particular vacuum environment.
A type of viscous gas flow where particles travel smoothly in regular paths, and the particle velocity is generally much slower near stationary objects in the flow path. No turbulent mixing occurs in viscous gas flow.
A crack, hole, or other pathway that allows gases to pass through from outside the vacuum system to inside the vacuum system.
A volume of trapped gas that enters the vacuum system when the system is pumped down.
See pump, Roots (blower).
A rotary plunger type pump where two symmetrically shaped impellors rotate in opposite directions inside the pump housing. Roots pumps are used where great volumes have to be pumped. Also known as lobe blower pump.
See bar and millibar.
See gauge, McLeod.
The average distance which a molecule travels between two successive collisions with other molecules of the gas.
See pumps, mechanical (roughing).
In vacuum systems, mechanical pumps are motor-driven pumps that move gas from the inlet port to outlet port using a mechanical mechanism, e.g. rotary vanes, scrolls, pistons, and diaphragms among others.
See gauge, MEMS Pirani.
The number of molecules per unit volume of gas.
Gas flow in which molecules interact primarily with surfaces in or along the flow path rather than with other molecules. Contrast with viscous flow.
Gas flow in which molecules interact primarily with other molecules, rather than with surfaces in or along the flow path. Contrast with molecular flow.
See pumps, momentum transfer.
A classification of pump where one part of the pump (either a solid component or molecular vapor) imparts preferred momentum to gas-phase molecules.
The mean volume flow through the cross section of the inlet port of a vacuum pump after the effect of all conductances have been accounted for.
A mechanical gasket in a circular shape made of an elastomer with a round cross section or metal such as copper. O-ring is sandwiched between two components and blocks a path which may otherwise allow gas to escape. Essentially, they help to prevents leaks when two components are joined together.
The process of gas molecules that are weakly bound to a surface, bound to pores or cracks in a material, or diffused into the bulk leaving the surface to become gas-phase molecules. Also known as surface desorption.
The pressure exerted by a particular species of gas molecules. According to Dalton’s law, the sum of the partial pressures of all the component species in a mixture is equal to the total pressure.
The SI unit of pressure equal to one newton per square meter. There are 101,325 pascals in one standard atmosphere. There are 1,000 Pa in 1 kPa. Named after French mathematician and philosopher, Blaise Pascal (1623-1662).
The process of molecular penetration of gases, vapors, or fluids completely through a material.
See gauge, piezo-resistive (vacuum).
See gauge, piezo-resistive (vacuum).
The ability of certain materials to change resistance or generate an electric charge in response to applied mechanical stress, and vice versa.
See gauge, Pirani.
See pump, piston (vacuum).
A type of positive displacement pump where the high-pressure seal reciprocates with the piston. Also called rotary piston (vacuum) pump.
A valve typically used to control the timing and quantity of gas flow.
See pumps, positive displacement.
A classification of pump that captures a volume of gas near the inlet and mechanically displaces it to the outlet. Often compression of the captured volume occurs between the inlet and the outlet.
A way of measuring how much force is acting over an area or the perpendicular force per unit area.
See gauges, vacuum (pressure).
A pressure unit defined as Pounds per Square Inch (of Gas).
Claw pumps use two claws rotating in opposite directions, like the Roots pump, to capture, compress, and exhaust the gas. Claw pumps can be used to effectively pump corrosive and abrasive gases. They are often combined with Roots pumps to achieve high pumping speeds and pressures in the millitorr range.
See pump, Roots (blower).
A vacuum pump that draws air by periodically changing the working volume of the pump.
A positive-displacement pump that consists of vanes mounted to a rotor that rotates inside a cavity. Invented by Charles C. Barnes in 1874.
A dry mechanical pump that contains two screw rotors which rotate inside a cylinder. The gas is trapped between cylinder and screw chambers and carried to the gas exhaust.
A dry mechanical vacuum pump design that utilizes two intermeshed spirals (i.e., scrolls) to displace and compress a crescent-shaped volume of gas from an inlet to an outlet region.
A vacuum component that moves gas molecules from a low-pressure region to a higher-pressure region. Vacuum-pump design is typically specific to its operating-pressure region, with the three main pressure regions being low vacuum (i.e., atmospheric pressure to ~1E-3 Torr), high vacuum (i.e., 1E-3 to1E-9 Torr), and ultra-high vacuum (i.e., less than 1E-9 Torr).
Mechanical pump that utilizes rotary motion to drive pumping mechanism. Examples of rotary pumps are screw pump, lobe blower pump, and rotary vane pump.
See pumps, mechanical (roughing).
See pumps, mechanical (roughing).
Commonly used term for evacuation of a vacuum chamber from atmospheric pressure to a pre-defined base pressure.
Graph describing a time-dependent pressure drop in a vacuum system; popular control instrument when designing and operating a vacuum system.
Time required to evacuate a chamber from atmospheric to a predefined base pressure.
The volume of gas that will flow past a given plane in a gas flow path in a given amount of time. Units are in volume per time (e.g., Liters per second). See also Volumetric Flow Rate.
The volume of gas that will flow past a given plane in a gas flow path in a given amount of time. Units are in volume per time (e.g., Liters per second). See also pumping speed.
A graphical representation of the pumping speed performance of a pump as a function of the pressure of the gas being pumped.
Decrease in density of gas.
See leak, gross (real).
See pump, reciprocating (vacuum).
Delay in time.
See pump, Roots (blower).
See pump, piston (vacuum).
See pumps, rotary (vacuum).
See pump, rotary vane.
See pumps, mechanical (roughing).
Vacuum pressure regime with pressures between 760 Torr and 1E-3 Torr.
Roughing a vacuum chamber indicates that it is being evacuated with a low-vacuum pump through a roughing line from atmospheric pressure to a pressure that is sufficiently low to allow a high vacuum pump to be engaged.
See pumps, mechanical (roughing).
The state or process that occurs when no more of something can be absorbed, combined with, or added.
The pressure exerted by a vapor which is in thermodynamic equilibrium with one of its condensed phases at the prevailing temperature.
See pump, screw.
See pump, scroll.
When various vacuum components, each with different values of conductance, are arranged in a single flow path, therefore requiring each gas molecule to transit through each vacuum component.
International System of Units (Abbreviation of French: Systeme International d’unites). The only system of measurement with official status in nearly every country in the world.
Transition of a substance directly from a solid state/phase to a gas state/phase.
The release of surface-bound molecules to the gas phase. For most vacuum systems, the main species of surface-bound molecule is water. Measured as a mass flow rate (e.g., in Torr-Liters/sec).
See gauges, thermal (conductivity).
See gauge, thermocouple.
A vacuum valve that can be controlled by the operator to be only partially open (or partially closed). Allows to control pumping speed by decreasing conductance (to throttle) between a vacuum chamber and a vacuum pump.
Term used to indicate molecular flow rate or mass flow rate. Identifies number of molecules flowing past a plane in a flow path. Units are in Pressure x Volume / Time (e.g., Torr-Liter/Sec).
Widely used (but non-SI) pressure unit in vacuum technology, equal to 1 mm of mercury in a historic barometer, and named after Italian physicist Evangelista Torricelli (1608-1647). Torr is still widely used in the US, and is therefore the pressure unit primarily used in this e-book.
Lowest attainable pressure in a vacuum system. In a vacuum pump, the lowest pressure that can be attained with that pump. Ultimate pressure is limited by the pumping speed of the vacuum pump and the vapor pressure of the sealing fluid, among other factors.
See ideal gas constant.
A “prefect vacuum” is defined as a space that is entirely devoid of any gas molecules. However, in vacuum technology, the more useful definition is a space in which the density of gas molecules is significantly reduced below that of atmospheric pressure, or where the mean-free-path is sufficient to conduct the desired vacuum process.
See chamber.
Any one of the many parts that are required to construct a functioning vacuum system, or parts required to undertake and control a vacuum process.
Generally, an organic or inorganic fluid that has a sufficiently low vapor pressure, as well as chemical and thermal stability to enable effective use as a lubricant and/or sealant in certain vacuum systems or processes.
See gauges, vacuum (pressure).
A two-part mixture comprised of vacuum-fluid molecules (i.e., base gel) and much larger molecules or particles (i.e., thickener). The components of the mixture are selected to demonstrate desirable mechanical, thermal, and other properties, and also demonstrate sufficiently low vapor pressure to allow its use as a lubricant and/or sealant in a certain vacuum systems or processes.
Vacuum piping components provide pathway for the gas to flow within a vacuum system. Examples of vacuum piping components are tees, nipples, elbows, crosses, reducers, and flanges or fittings.
See pump, vacuum.
A body of knowledge and related skills required to undertake processes and measurements under conditions of sub-atmospheric pressure.
The term “vapor” is often used when a material may be present in several phases within a vacuum chamber at a given pressure. For example, during thermal evaporation of a metal, metal generally exists as a solid source, then as a pool of liquid metal as the temperature increases, and finally as a metal vapor evaporating from the surface of the liquid. The evaporated metal vapor will re-condense into a solid when it adsorbs onto any relatively cool surface (i.e., a substrate).
Conversion of a substance from the liquid state/phase to the gas (vapor) state/phase.
Part of a vacuum system that controls the flow of outside air (or gas) into the vacuum chamber.
See leak, virtual.
