A Guide to Terminology

Pneumatics, in common with most advanced technologies, has its own vocabulary which, even to those who have spent years in the industry, can be both confusing and, at times, difficult to remember.

The following is not intended to be a definitive guide; instead, it covers the most commonly used terms and expressions and is designed for use by newcomers and old hands alike.

Pneumatic Terminology

Actuator A device for converting the energy of compressed air into work. The term is generally applied to cylinders.
Aftercooler A device for cooling compressed air as it leaves the compressor, to prevent excessive condensation occurring further downstream.
Air Chuck Commonly called grippers; pneumatically powered jaws are used to grip a workpiece - typically used for pick and place applications.
Automatic Drain Designed to be installed at strategic points throughout the pneumatic system, to allow condensate to be automatically removed.
Bar Standard measurement of pressure. One bar is approximately equal to atmospheric pressure.
Bore Size The diameter of a piston operating within an actuator.
Boyles Law At a constant temperature, the volume of a given quantity of any gas is inversely proportional to the pressure upon the gas; i.e. V is proportional to 1/P, or PV = a constant. True for a perfect gas. Named after Robert Boyle, (1627-1691).
Cv A Cv of one is equal to a flow rate of one US gallon of water per minute, with a pressure drop of one psi.
Cascade A type of pneumatic circuit designed to overcome the problems associated with trapped pressure signals.
CETOP (Comité Européen des Transmissions Oléo Hydrauliques et Pneumatiques)
A European pneumatic standard designed with the aim of component interchangeability.
Check Valve A device which allows compressed air to pass through in one direction, but prevents it returning along the same path. SEE NON-RETURN VALVE
Compressor A machine for compressing atmospheric air so that it can be used to drive pneumatic devices. SEE RECIPROCATING AND ROTARY COMPRESSORS.
Cushioning A facility available on actuators to cushion at the end ofstroke to prevent sudden impact.
Cylinder A linear-actuator.
Dew Point The temperature at which the water vapour present in air saturates the air and begins to condense, i.e. dew begins to form.
Double Acting Cylinder A cylinder which is actuated by compressed air in both extending and retracting strokes.
F.R.L. Air preparation unit consisting of Filter, Regulator, and Lubricator.
Filter A device for removing contaminants from compressed air, typically moisture, oil and solid particles.
Flow The flow of air through a pneumatic system. Expressed in normal litres per minute, ln/min., never as NL/min.
kv A kv of one is equal to a flow rate of one litre of water per minute, with a pressure drop of one bar.
Manifold A device which is capable of dividing a single compressed air source into several outlets. The most common application is for supplying air to a number of valves secured to a common mounting base, i.e. a valve manifold.
Newton The derived SI unit of force. The forced required to give a mass of one kilogram an acceleration of one metre per
second per second. Symbol N. Named after Sir Isaac Newton (1642-1727).
Non Return Valve A device which allows compressed air to pass through in one direction, but prevents it returning along the same path. SEE CHECK VALVE
Pascal The derived SI unit of pressure, equal to 1 newton per square metre. Symbol Pa. (100,000 Pa = l kgf/m2). Named after Blaise Pascal (1623-1662).
Poppet Valve A type of valve construction whereby sealing is achieved by means of a flat seal against an orifice.
Reciprocating Compressor A compressor in which air is pressurised by means of piston and cylinder.
Regulator A device for adjusting the pressure of compressed air, typically used to reduce available pressure to a suitable working pressure.
Relative Humidity The ratio of the pressure of the water vapour actually present in the atmosphere to the pressure of the vapour which would be present if the vapour were saturated at the same temperature.
Ring Main A term used to describe a compressed air piping system which is arranged in a complete loop, i.e. a ring.
Rodless Cylinder A cylinder whose moving element actuates within the length of the cylinder body and does not use a conventional extending piston rod. Space saving is therefore achieved.
Rotary Compressor A compressor which uses rotating vanes or meshing screws to pressurise air.
Single Acting Cylinder A cylinder which uses compressed air to actuate the piston in one direction but uses spring force to achieve movement in the opposite direction. Capable of performing work only in the driven direction.
Slide Unit A precise linear actuator which uses a guide mechanism to improve accuracy of travel and/or provide a facility to limit rotation about its axis of travel.
Slide Valve Directional control valve where sealing is achieved by sliding a lapped metal seal across the valve’s orifices.
Solenoid Valve A valve which is activated with the use of an electrically operated solenoid.
Speed Controller A steplessly variable orifice for varying the flow of compressed air thus providing a speed control facility for actuators.

Electronics Terminology

EEPROM or E2PROM Electronically Erasable Programmable Read Only Memory. A ROM chip (see below) which can be electronically erased.
I/O Input/Output. A statement of the number of inputs and outputs for a specific device or system.
Ladder Logic Complex programming language used for configuring PLC’s (see below).
PID Process Integer Derivative
PLC Programmable Logic Controller. Sometimes called Programmable Controller. Designed to control the sequencing of electronic equipment.
RAM Random Access Memory. A memory chip which is used to provide working space for operations in progress at any one time.
ROM Read Only Memory. A memory chip which, once written to, cannot be erased. Used to store set parameters.