ABS: A non-toxic plastic sometimes used as a piping material in compressed air installations
Absolute Pressure: A pressure at absolute zero (i.e. a perfect vacuum.) Absolute Pressure equals the sum of the Atmospheric Pressure and Gauge Pressure
Absolute Temperature: The temperature measured from Absolute Zero, using the Kelvin Scale
Activated Carbon: A form of carbon characterised by high adsorptive capacity for gases, vapours or solids
Adsorption: The natural action of a gas, vapour or liquid being attracted to and held on the surface of a solid
After Cooler: A heat exchanger for the reduction of temperature of air after compression
After Cooling: The removal of heat from the air after compression is complete
Air Compressor: A machine which compresses air to a pressure higher than its inlet pressure
Air Receiver: A tank in which compressed air is stored, also called a pressure vessel
Ambient Temperature: The temperature of the surrounding environment in which the equipment is working in
Atmospheric Pressure: The pressure exerted by the atmosphere
Ball Valve: A device that shuts off flow by means of a hollow spherical component (ball)
Bourdon Tube Gauge: An instrument that senses and records pressure. The pressure energy detected is converted into mechanical movement, i.e. moving a pointer on a dial
Carbon Dioxide: A colourless, odourless, incombustible gas. It is a major greenhouse gas, contributing to climate change (global warming)
Carbon Monoxide: A colourless, odourless, incombustible, toxic gas
Celsius: A temperature scale on which the freezing point of water is 0 degrees Celsius and the boiling point of water is 100 degrees Celsius (at one atmosphere of pressure. Celsius is the term preferred for Centigrade)
CE Mark: A mark that denotes compliance with European directives
CFM: A commonly used abbreviation for ‘cubic feet per minute’, a figure applied to the output of an air compressor
Chemical Energy: The energy in chemical bonds holding the atoms of a compound together. Food, wood, batteries, and fossil fuels possess chemical energy
Coalesce: This is the process of bringing together fine liquid particles or mists together to form larger particles as liquid droplets
Competent Person: A legal phrase to identify a person who performs the activities required by the Pressure Systems Safety Regulations for compressed air systems. The competent person may be required to produce schemes of examination or to do examinations
Compressor Capacity: The actual volume rate of flow compressed and delivered at the standard discharge point, at stated inlet conditions, usually expressed in terms of Free Air Delivered
Condensate: The water formed in a compressed air system from water vapour due to a decrease in air temperature and or an increase in pressure. Often contaminated with oil and solid particles
Constant: A quantity that does not change its value, no matter what happens to other related variables, usually represented by the letter K
Coolant: A fluid (liquid or gas) used to remove heat from compressed air
Demand: The amount of compressed air required by tools and equipment
Desiccant: A chemical possessing a strong affinity for water
Dew Point: The temperature at which air is fully saturated with water vapour at the prevailing pressure
Directly Proportional: The process by which two quantities decrease or increase with each other
Discharge Outlet (port or valve): A hole or valve through which gas or air leaves the compressor
Displacement: The volume displaced by the compression element of the first stage per unit of time (e.g. litres per second, cubic feet per minute)
Distribution System: A network of pipes installed from one point to another in a factory that delivers compressed air to a point of use
Drains: Devices that collect condensate from a compressed air system. These are often fitted to air receivers, filters, dryers or piping
Dryer: A device that reduces the water vapour content of the compressed air
Efficiency: Something that is produced with minimum effort or energy
Filter: A device that removes contaminants from compressed air
Filtration: A physical process that selectively removes gases, vapours, liquids or solids from compressed air by providing a barrier to such particles
Fahrenheit: A temperature scale on which the freezing point of water is 32 degrees F and the boiling point of water is 212 degree F (at one atmosphere of pressure)
Flow Controller: A device which varies the amount of air flowing through it
Fossil Fuels: Carbon-rich fuel formed from the remains of ancient animals and plants. Coal, oil, and natural gas are all fossil fuels
Foul Sewer: The main drains used for the disposal of waste water of domestic or industrial origin, that comes under the responsibility of the local water authority
Free Air: Air that is under atmospheric conditions at the inlet point which is unaffected by the compressor
Free Air Delivered (FAD): The free air delivered by a compressor is the actual volume which it will compress and deliver at the stated pressure, at the intake temperature and pressure. FAD is expressed in cubic feet per minute or litres per second.
Full Load: The state in which a compressor is producing air and operating at full capacity
Galvanized Steel: This is steel coated with zinc to reduce the effects of corrosion
Gauge Pressure: The pressure that is shown or indicated on a gauge or instrument
Generator: A device or machine that converts mechanical energy into electrical energy
General Gas Law: This is a law which states how pressure, volume and temperature interact
Hazard: This is anything that can cause harm e.g. in the workplace: lifting, machining, working from ladders
Heat Recovery: A process where heat which is generated by a compressor, that would otherwise be wasted, is saved and re-used
High Pressure: This is system pressure which is over 40 bar
Higher Efficiency Motor (HEM): A Motor that uses up to 3% less electricity than a standard motor, by virtue of an improved design
Humidity: The degree of water vapour in the atmosphere
Inlet Port (or valve): A hole (or valve) through which air enters the compressor
Inter Cooling: The removal of heat from the air between stages in multi-stage compression
Inversely Proportional: The process by which one quantity decreases when another increases
Kinetic Energy: The energy possessed by a moving object
Low Pressure: This is pressure generally considered to be between atmospheric pressure and 20 bar
Lubricant: A fluid (generally an oil) used to overcome friction between surfaces that come into continuous moving contact
Normal: This is a term represented by the prefix ‘n’ denoting a standard condition of temperature and humidity
Non-Renewable Energy Resource: This is an energy resource that is either replenished very slowly or is not replenished at all by natural processes
Off Load: This refers to a compressor that is switched on i.e. running but the compressor is not producing air
Oil Injected (lubricated): An air compressor in which oil is injected into the chamber during the compression process to limit the temperature rise in the chamber
On Load: This refers to a compressor that is producing air, either at part load or full load
Over Pressurisation: This is when the pressure of a compressed air system is exceeded
Packaged Air Compressor: A self-contained unit consisting of a compressor and prime mover together with accessories for its safe operation
Parameter: A physical quantity that can be measured, e.g. volume, pressure, etc.
Part Load: This refers to a compressor when it is producing air, but not at full capacity
Pattern of Use: This describes the way in which tools and equipment are used
Piping: A pipe or system of pipes used for the conveyance of compressed air
Piston: A mechanical device which has a plunging or thrusting motion
Pneumatics: This refers to the science systems driven by compressed air
Point of Use: The point at which the compressed air performs its useful work, i.e. powering air tools or equipment
Positive Displacement: The action of a compressor type that traps and compresses a measured volume of air between its fixed and moving parts that causes the air’s pressure to rise and reduce its volume and delivery to a system
Potential Energy: This is stored energy that can be released or harnessed to do work (chemical energy is a form of potential energy)
Power: The rate at which energy is transferred or converted per unit of time. It is quoted in Watts
Pressure Band: The difference between the specified upper and lower limit of pressure in which compressors are required to operate
Pressure Drop: The drop in pressure between any two specified points in a system
Pressure Ratio: (total). The ratio between the absolute discharge pressure and the absolute inlet pressure
Pressure Relief (Safety) Valve: A device to limit the maximum system pressure by allowing the escape of the compressed air into the atmosphere when a dangerous limit has been reached. This device is also referred to as a safety valve or a pressure relief valve (PRV)
Pressure Reducing Valve (Pressure Regulator): A device which reduces the incoming pressure to a lower level and maintains it irrespective of inlet pressure and outlet flow rate changes
Pressure Vessel: This is an air storage tank or air receiver
Primary Energy Source: An energy source available directly from the environment e.g. coal, oil, natural gas, sun, wind, geothermal energy and hydropower
Prime Mover: A self-propelled machine, e.g. an electric motor or internal combustion engine, used to drive machinery
Purity: This is something that is free from contaminants. Air purity is the degree of cleanliness required for an application (often referred to as “air quality”)
Reciprocating: A machine in which a piston moves alternately backward and forward in a cylinder
Refrigerant: A fluid used for cooling that, when changing from liquid to gas, takes heat from its surroundings (in this case compressed air)
Refrigerant Dryer: A device which recycles a fluid (a refrigerant) between liquid and gas stages producing a cooling effect on the compressed air
Renewable Energy: An energy resource that can be replenished within a finite time
Ring Main: An air main that begins and ends at the compressor so that every usage point has two possible routes of supply
Risk: The chance, great or small, that someone will be harmed by a hazard
Roots Blower: A positive displacement rotary machine used for compressed air applications at low pressures up to 1.5 bar
Rotary: Compressors where the air is compressed by circular motion
Run-On Timer: A time related control that switches off the prime mover when the compressor has been on off-load for a specified period of time
Secondary Energy Source: These are energy sources derived from a primary energy source. The most common secondary energy source is electricity
Sensor: An electronic device used to measure a physical characteristic such as pressure or temperature and converts the information into an electronic signal
Service Pipe: A pipe that delivers gas, oil, water, steam or air to and around a site
Shut Off Valve: A device incorporating a means to close off supply of air flow
Signal Switch: A switch (mechanical or electronic) which responds to the signal from a sensor
Single Line Main: Piping arrangement whereby various branches are taken from a single pipe such that each usage point has one route of supply
Standard: This indicates that the figures quoted are derived at a standard temperature and humidity, the ‘s’ prefix is used, e.g. scfm – standard cubic feet per minute
System Pressure: This is the normal operating pressure, often referred to as “working pressure”
Tertiary Energy Source: An energy source derived from secondary energy sources
Thermodynamics: This is the science of the conversion of heat to other forms of energy
Utility: A domestic or industrial service company, e.g. gas, oil, water, electricity company
Variable Speed Drive (VSD): This is an electronic device which when fitted to a motor can vary the speed of a compressor and vary its air output
Water Vapour: This is the gaseous state of water
