Oil and Vacuum Glossary

Absolute Pressure

The measurement of pressure referenced to theoretical absolute zero pressure (perfect vacuum).  For example, 0" of Hg absolute is theoretical perfect vacuum and 29.92" Hg absolute is atmospheric pressure at sea level.  See Relative Pressure.


The binding of gas in the interior of a solid or liquid.


The actual pumping speed in cubic feet per minute at a given pressure (Actual Cubic Feet per Minute or Cubic Feet per Minute).


A chemical added to a base fluid in order to improve specific properties of the lubricant such as fluid life, lubricity, wear protection, rust protection, etc.


The condensing of gas on the surface of a cooled solid such as in a liquid nitrogen vacuum trap.

Air-Inlet Valve

A valve used for letting atmospheric air into a vacuum system or chamber. Also knows as a vent valve or vacuum breaker.

Anti-Foam Agent

An additive that causes foam to dissipate more rapidly through the combination of small bubbles into large bubbles.


A chemical added to a petroleum product to increase its oxidative resistance in order to prolong its service life.

Antisuckback Valve

A valve that prevents the migration of oil and air from a vacuum pump into the system, when the pumps stops and the system is under vacuum. The failure of an antisuckback valve when a pump is powered off could allow oil to flow back through the inlet into the vacuum system.

Anti Wear Agent

An additive that minimizes wear caused by metal-on-metal contact. It forms a film on the metal surface and is activated by heat and pressure.

Atmospheric Pressure

The pressure of the atmosphere at a specified place or elevation  The normal or “standard” atmosphere has been defined as the pressure exerted by a mercury column 760 mm (29.92") in height at 0 degrees C.

Auto-Ignition Temperature

Minimum temperature at which a combustible fluid will burst into flame without the assistance of an extraneous ignition source. This temperature is typically several hundred degrees higher than the flash and fire point.


The back flow of the working fluid (typically oil) of a vacuum pump upstream toward the vessel being evacuated.  Backstreaming of oil is a slow process that is enhanced when poor quality oil spent or contaminated oil is used. Vacuum traps are effective at minimizing oil backstreaming.

Back Pressure

Resistance to flow in a system.

Base Oils

Base stocks or blends used as an inert ingredient in the manufacturing of automotive and industrial lubricants.

Base Stocks

Refined petroleum oils that can either be blended with one another or supplemented with additives to make lubricants.

Belt-Drive Pump

A pump with the motor drive provided by a belt and pulley which is attached to the pump shaft. The ratios of the diameters of the pump and motor pulleys determine the actual rotational speed of the pump.

Boundary Lubrication

A form of lubrication that is effective in the absence of a full fluid film, enabled by additives in the lubricating oil that prevent excessive friction and scoring by forming a film whose strength is greater than that of oil alone. These additives include oiliness agents, compounded oils, anti-wear agents, and extreme pressure agents.

Carbon Residue

Coked material formed after lubricating oil has been exposed to high temperatures. Many consider that the type of carbon found is of greater significance that the quantity.

Cold Trap or Condenser

A vessel inserted into a vacuum system that uses a refrigerant or other cooling method to condense vapors present in the system.

Compression Ratio

The ratio between the outlet pressure and the inlet pressure of a pump for a specific gas.

Compound Mechanical Pump

A mechanical pump having two or more stages of compression.

Condensation Rate

The number of molecules which condense on a surface per square cm/second.


The actual capacity of a piping system, typically measured in liters/sec.. Conductance in a vacuum system can be limited by line size, length and configuration.


The removal of gas and vapors from a substance under vacuum.

Direct-Drive Pump

A pump with the motor drive provided by a direct coupling to the pump rotor shaft. The rotational speed of the motor is the rotational speed of the pump.


The geometric volume swept out per unit time by the working mechanism of mechanical pumps at normal rotational speeds. Also called free air displacement. This value, being theoretical, is not usable by end-users. It is mainly a standard used by vacuum pump manufacturers.


A lubricant’s ability to separate from water.


An additive which chemically neutralizes acidic contaminants in the oil before they become insoluble and fall out of the oil to form sludge. Particles are kept finely divided so that they can remain dispersed throughout the lubricant.

Dry Ice Trap

A type of cold trap that uses a slurry of dry ice and alcohol to cool the trap surface and condense vapors.

Dry Vacuum Pump

A type of vacuum pump that does not us oil-based lubricants in the pumping chamber.


Describing a state of an immiscible fluid component. Minute quantities of a fluid (typically water) can be dissolved or absorbed into the oil, but excess quantities can be most harmful to equipment due to the entrainment leaving gaps in the lubricated areas.

Fire Point

Lowest temperature at which a combustible fluid will burst into flame in the presence of an extraneous ignition source. Very little additional heat is required to reach the fire point from the flash point.

Flash Point

Lowest temperature at which vapor from a sample of a petroleum product or other combustible fluid will “flash” in the presence of an ignition source. The flash can be seen in the form of a small spark over the liquid.


A possible reaction of an oil when mixed with air. This entrained air can result in reduced film strength and a performance reduction.

Foam Inhibitor

An additive which causes foam to dissipate more rapidly. It promotes the combination of small bubbles into large bubbles which burst more easily.


Vacuum line connecting the exhaust of a high vacuum pump (such as a turbomolecular pump) to the inlet of a mechanical vacuum pump.

Fractional Distillation

A separation process which uses the difference in boiling points of liquids.


Resistance to motion on a surface or by a substance as a result of its contact with another surface or substance. Sliding friction is that which occurs between two solid bodies, while fluid friction is that which occurs between the molecules of a fluid in motion. Both types of friction can be wasteful in power and energy, and sliding friction causes wear.


Gas is defined as the state of matter in which the molecules are practically unrestricted by intermolecular forces so that the molecules are free to occupy any space within an enclosure. In vacuum technology the word “gas” has been loosely applied to both the permanent (non-condensable) gases and vapors, or condensable gases.

Gas Ballast

The bleeding of a gas (typically air) into the compression chamber of a mechanical pump to minimize condensation of condensable vapors within the pump.


A type of lubricant composed of a fluid (typically lubricant oils) thickened with a material that contributes a degree of plasticity (typically soaps). Just as viscosity is the basic property of lubricating oil, consistency is the basic property of grease. Consistency is measured in terms of penetration, tested in terms of tenths of a millimeter that a standard cone acting under the influence of gravity penetrates the sample under controlled test conditions. the greater penetration, the softer the grease.

High Vacuum

Vacuum range typically defined from 10-3 to below 10-7 Torr.


A compound containing hydrogen and carbon only. Hydrocarbons may exist as solids, liquids or gases (coal, crude oil and natural gas).


Compounds of hydrogen and carbon of which petroleum products are typically examples. Petroleum oils are generally grouped into two parts: Napthenics, which possess a high proportion of unsaturated cyclic molecules; and paraffinic, which possess a low proportion of unsaturated cyclic molecules.

Hydrodynamic Lubrication

A type of lubrication effected solely by the pumping action developed by the sliding of one surface over another in contact with an oil. Adhesion to the moving surface draws the oil into the high-pressure area between the surfaces, and viscosity retards the tendency to squeeze the oil out. If the pressure developed by this action is sufficient to completely separate the two surfaces, full-fluid-film lubrication is said to prevail.

Ideal Gas

A gas which obeys Boyle’s Law and has zero heat of free expansion (Charles’ Law). Also known as a perfect gas.


The rapid inward collapsing of the walls of a vacuum system or device as the result of failure of the walls to sustain the external atmospheric pressure.

Inlet Pressure

The total pressure measured at the inlet of a vacuum pump.

Isolation Valve

A valve that seals off a vacuum system from the vacuum pump when the pump is off.


A hole or porosity in the wall of a vacuum system that allows a gas to pass into the vacuum system.

Leakage Rate

The rate of flow of a gas through a leak.

Low Vacuum or Rough Vacuum

Vacuum range from atmospheric pressure to approximately 10-3 torr

Mechanical Pump

A pump which moves the gas by the cyclic motion of a system of mechanical parts such as pistons, eccentric rotors, vanes, screws, valves, etc.

Micron (Micron of Mercury)

Unit of pressure equal to .001 Torr. Also known as a millitorr.

Millimeter of Mercury

Unit of pressure equal to 1 Torr.

Non-Condensable Gas

Permanent gases inside a vacuum system, not to be confused with vapors.


The escape of gas from materials within a vacuum system. Is the primary limiting factor in the ultimate vacuum obtained in a high vacuum system


A form of chemical deterioration to which all petroleum products are subject to, and involves the addition of oxygen atoms resulting in degradation. It is accelerated by higher temperatures above 160°F, with the rate of oxidation doubling by each 20° increase. With fuels and lubricant oils, oxidation produces sludges, varnishes, gums, and acids, all of which are undesirable.

Oxidation Stability

Resistance of a petroleum product to oxidation, therefore increasing its potential service or storage life. Since the life of many lubricants can be well over a year, simulations are used to show the time required for a sample to develop a specified degree of oxidation under accelerated conditions.

Partial Pressure

The pressure due to a gas or vapor component of a gaseous mixture. For example, in atmospheric pressure, nitrogen has a certain partial pressure that makes up a large percentage of the total pressure.

Pour Point

A significant factor in cold weather start-up, it is a widely-used low temperature flow indicator, depicted as 5°F above the temperature to which a normal liquid petroleum product maintains fluidity.

Pumpdown Curve

A graph representing the relationship between pressure and time. Used to determine the time required to achieve the desired operating pressure in a system with a given pump.

Pumping Speed

The volume of gas per unit of time which the vacuum pump is able to remove from the system. Pumping speed is often expressed in CFM (Cubic Feet per Minute), L/M (Liters per Minute), M3/Hr (Cubic Meters per Hour) or L/S (Liters per Second).

Rate of Rise

The timed rate of pressure increase during a given interval in a vacuum system which is isolated from the pump by a valve.

Roots Blower Pump

A rotary blower pump having a pair of inter-engaging impellers. This type of pump is usually used in conjunction with a backing pump to increase the pumping speed of a vacuum system over a certain pressure range.

Rotary Vane Vacuum Pump

A rotary vane vacuum pump is an oil-sealed rotary displacement pump. The pumping system consists of a housing, an eccentrically installed rotor, vanes that move radially under spring force and the inlet and outlet. These pumps can include either one or two stages.

Rotary Piston Vacuum Pump

A rotary piston vacuum pump is typically an oil-sealed rotary displacement pump. The pumping system consists of a pistons instead of vanes for compressing the gas stream. These pumps can include either one or two stages.

Rust Inhibitor

A lubricant additive for protecting ferrous (iron and steel) components from rusting caused by water contamination or other harmful materials from oil degradation. Some rust inhibitors operate similarly to corrosion inhibitors by forming inert films on metal surfaces. Other rust inhibitors absorb water by incorporating it into a water-in-oil emulsion so that only oil touches the metal surfaces.


Volume flow referenced to standard conditions. Standard cubic feet per minute.

Shear Stress

A unit of frictional force overcome in sliding one layer of fluid along another. This is typically measured in pounds per square foot, with pounds representing the frictional force, and square feet representing the area of contact between the sliding layers.


The collective name for contamination in an lubricated system and on parts bathed by the lubricating oil. This includes decomposition products from the fuel, oil, and particulates from sources external to the system.


The quantity of gas in pressure-volume units at a specified temperature flowing per unit of time across an open cross section of a pump or pipe line.


Unit of pressure equal to 1 mm of Mercury.

Total Pressure

Sum of all the partial pressures in a gas mixture.


An accessory used condense or absorb vapors or particles present in the vacuum.

Vapor Pressure

The measure of a liquid's volatility. The higher the vapor pressure, the more volatile the liquid, and the more readily it will evaporate.

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.


Any pressure in a system that is less than the ambient atmospheric pressure.

Vacuum Cooling

A process for lowering the temperature of a material by subjecting it to vacuum conditions, causing vaporization of a liquid.

Vacuum Drying

The removal by evaporation of liquid from a substance in a vacuum. When the liquid is water, the process is sometimes called vacuum dehydration.

Vacuum Gauge

Any instrument used to measure pressure in a vacuum system.


A substance in gas phase which is condensable at ambient temperatures.


A deposit resulting from oxidation and polymerization of fuels and lubricants. Similar to but softer than lacquer.


A property from which a fluid’s resistance to movement can be evaluated. The resistance is caused by friction between the fluid and the boundary wall and internally by the fluid layers moving at different velocities.


The property of a liquid that defines its evaporation characteristics. Of two liquids, the more volatile will boil at a lower temperature and will evaporate faster when both liquids are at the same temperature. The volatility of petroleum products can be evaluated by tests for flash point, vapor pressure, distillation, and evaporation rate.