Terminology in Instrumentation

The body of terms used with a particular technical application in a subject of study, theory, profession, etc.

ABSAcrylonitrile Butadiene Styrene. A rugged plastic compound typically used for housings, some external parts. A form of ABS is also used for low-pressure air piping systems in harsh environments.
AflasAn elastomer used for high temperature/high purity or highly aggressive applications; particularly suited to ozone-treated water. Aflas® is a trademark of 3M
ASQAmerican Society for Quality
ASTMShort for American Society for Testing and Materials. An organization created to establish conformity in American Class Standards. Click here for more information on “What are the Different ANSI Classes for Valves?”
ANSIAmerican National Standards Institute
BCFBead and crevice free. Also known as fusion. A means of connecting pipes, valves and fitting via heat fusion, with a perfectly smooth internal joint.
BPVRBack Pressure Regulating Valve
Breaking PressureThe minimum pressure required to produce flow through a valve.
BS / BSPBritish standard, British Standard Piping. A piping specification
Buna or Buna-NNitrile rubber, used to make O-rings and other seals used in valves. Buna-N is the least expensive type of seal, and it lacks the chemical compatibility of other more costly elastomers.
ChemrazA fluorinated elastomer used for high temperature/high purity or highly aggressive applications. Chemraz® is a trademark of Green-Tweed.
CNCComputer numerically controlled. Popular type of control system for vertical machining centers, lathes, injection molding machines, and other tools used to fabricate a valve.
Corzan / CPVCChlorinated polyvinyl chloride. While not as popular as PVC, it is able to withstand higher temperatures.
CSACanadian Standards Association.
DiverterA three-way valve; the flow can be diverted from one outlet to another, or different inlets can be selected and sent to a common outlet.
EPDMEthylene propylene diene monomer. A popular rubber seal material, compatible with a wide range of chemicals.
FlangeA type of pipe fitting that attaches via nuts and bolts.
FlareA type of pipe fitting that uses a socket and a type of union nut to form a connection with minimal crevice, for ultrapure processes. Usually seen on fluoropolymer or natural polypropylene valves.
Flow Coefficient (Cv)The definition of a Cv is the ability to pass 1 gallon per minute of water at 60 degrees Fahrenheit with a 1 pound pressure drop. For example, a Cv of 10 (in at 100 psig out at 99 psig) will pass 10 gallons a minute of water.
Flow PatternsA diagram showing how flow can be directed using a particular valve. (See the “Flow Patterns” box below for further explanation.)
FRPFiberglass Reinforced Pipe
GPMGallons per minute. Express volume of flow.
GPPGlass-filled polypropylene. Offers the chemical resistance of polypropylene, with glass fibers added for strength.
HalarEthylene-Chlorotrifluoroethylene. Used for some external components; it is also a valve body material for high temperature/high purity applications.
IAPDInternational Association of Plastics Disbributors. Formerly NAPD, National Assoc. etc.
IBBTIron Body Bronze Trim
ISAThe Instrumentation Systems and Automation Society. Formerly Instrument Society of America.
JorlonA patented product made by Jordan Valve, similar to Teflon, used for diaphragms.
KalrezA fluorinated elastomer used for high temperature/high purity or highly aggressive applications. Kalrez® is a trademark of DuPont Dow Elastomers.
KynarBrand of Polyvinylidene fluoride. A dense, high purity plastic that is used in critical applications, such as semiconductor manufacturing.
Laminar FlowSometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. In fluid dynamics, laminar flow is a flow regime characterized by high momentum diffusion, low momentum convection, and velocity independence from time. It is the opposite of turbulent flow. In nonscientific terms laminar flow is “smooth,” while turbulent flow is “rough.”
National Electrical ManufacturersUsed in valve terminology to define the level of external resistance an enclosure or solenoid coil is suited. i.e. NEMA 1 is dust tight, NEMA 9 is explosion proof, etc.
NaturalDescribes resins, frequently PP or PVDF, that have not had colorants, fibers, or other components added prior to processing. Sometimes mistakenly interchanged with “virgin”.
NCNormally closed, valve stays closed in de-energized state; opens when energized.
NEMANational Electrical Manufacturers Association defines the level of external resistance. i.e. NEMA 1 – Dust tight, NEMA 9 is explosion proof.
NONormally open, valve stays open in de-energized state; closes when energized.
NPT National Pipe Thread
O-RingA type of seal. An O-ring is a round elastomeric ring, ideally suited to be a compressed, static seal between non-moving parts. O-rings can be used as a face seal on a valve and used on rotating shafts inside a valve.
OS&YOpen Stem and Yoke (valve)
Outside Screw and Yoke (gate valve mechanism)
Outside Stem & Yoke (valve)
PECTFEEthylene-chlorotrifluoroethylene. This material used in HALAR brand, for some external components; it is also a valve body material for high temperature/high purity applications.
PET / PETRAPolyethylene terephthalate. (PETRA is a brand) Used on certain housings.
PneumaticA pneumatic valve uses pressure or air to open and close the valve.
PP or PPL, PolypropyleneA lightweight plastic that offers relatively high purity characteristics at a price well below PVDF or PTFE. Impervious to many chemicals.
Pressure Differential or Pressure DropThe difference between the inlet and the outlet pressure through a valve. The outlet pressure is lower than the inlet pressure due to the restriction caused by the valve.
PRVPressure Reducing Valve
PSIPounds per square inch. Used to indicate the amount of pressure in a given piping system.
PTFE BellowsA sealing mechanism that is made of PTFE, formed in a bellows shape, used on many solenoid valves.
PTFEPolytetrafluoroethylene, a type of fluorinated thermoplastic with outstanding chemical resistance, low leachability, and excellent lubricity.
PVCPolyvinyl chloride. This is the most popular material used for plastic piping systems.
PVDFPolyvinylidene fluoride. A dense, high-purity plastic that is used in critical applications, such as semiconductor manufacturing. Plast-O-Matic is an authorized reseller of Kynar® PVDF. Kynar is a trademark of Elf-Atochem.
PVFPipes, valves fittings. Used to describe a segment of the plastics industry or distributors who specialize in these products.
RegrindThermoplastic that has been processed once, then is placed in a grinder to be shredded/pelletized for re-molding. In injection molding, runners etc. are often re-ground. No thermoplastic can be successfully reground and remolded indefinitely; eventually the molecular bond begins to break down and the plastic is no longer usable.
Rolling DiaphragmA type of seal, also senses pressure. This is a diaphragm formed in a convoluted shape. It gets its name because as the stem moves, the diaphragm “rolls” at the convolution. It is frequently used in a manner similar to a u-cup, that is, to seal the gap between a linear moving shaft and the valve body.
Solenoid ValveA valve that uses an electromagnetic coil for actuation.
SpigotA type of fitting, essentially a section of pipe fused cleanly into a valve. This protruding pipe is then fused into the piping system. Usually found in high purity systems.
TeflonThis is the brand name for a number of fluorinated polymers manufactured by E. I. DuPont de Nemours. Many valve manufacturers use this term illegally, when in fact their products are not Teflon® but generic PTFE, PFA etc.
TempriteThis is a formulation of Corzan® CPVC that is used for injection molded valve bodies.
Thermoplastic, ThermosetTwo basic types of plastic resins. Thermoplastics are resins that can be reground after molding and molded again. Thermosets can be molded once only. They tend to be denser materials for special purposes. PVC is a thermoplastic. A PVC valve could conceivable be reground, then molded into a coffee mug. The resin used on a solenoid coil is a thermoset. A good analogy is paraffin wax vs. paraffin paste; both are petroleum products, but the wax can be melted and reformed while the lubricant cannot. Just as paraffin cannot be melted and reshaped indefinitely, no thermoplastic can be successfully reground and remolded indefinitely. Eventually the molecular bond begins to break down and the plastic is no longer usable. In another popular analogy, thermosets are often compared to an egg; once the egg is hard boiled it can’t be returned to a liquid and recooked as a sunny side up.
3 Way VALVES3 Way Valves has three (3) ports. Depending on the particular valve, all three (3) ports may be open, two (2) ports may be open, or all ports may be closed.
2 Way ValvesA 2 way valve as a single inlet port and a single outlet port.
U-CupA type of seal. A u-cup is an O-ring formed into a u-shaped channel. Liquid or air pressure “inflates” the u-cup and affects a seal. The u-cup is used in instances where an O-ring is not desirable.
VirginDescribes thermoplastic resins that have no “regrind” in the processing mix. Sometimes mistakenly interchanged with “natural”.
ViscosityIs a measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as “thickness”, or resistance to flow.
VitonA fluorinated elastomer used in making O-rings and other seals. Viton® is a trade mark of DuPont Dow Elastomers.
WOGWater/Oil/Gas, describes a common type of brass valve.
X-ValveA term used to describe any type of custom valve. “Q-valve” is used to describe custom ball valves.
What is a Cv?The Cv, also known as the flow coefficient, is the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.
Pressure Reducing Valve (PRV)The purpose of a pressure-reducing valve is to reduce the pressure from an upstream pressure to a desired downstream pressure. A PRV is normally open; an increase in pressure on the downstream side of the valve causes it to start modulating closed.
Back Pressure Regulating Valve (BPRV)A backpressure regulator’s purpose is to maintain a constant upstream pressure by relieving excel pressure in a process. A BPRV is normally closed; an increase in pressure on the upstream side of the valve causes it to start modulating open.
Temperature RegulatorTemperature regulators maintain a constant temperature in a process by inserting a thermal probe (bulb) in the process where the temperature needs to be maintained. This thermal system consists of a liquid or vapor interface. As the liquid boils, it creates vapor pressure, which will exert pressure to overcome the spring tension on the valve body. This movement allows the valve to move to allow steam or other medium through the valve.
Ball ValveBall valves are generally used for on off service and can be turned 90° which turns a ball with a port (hole) through it so the hole is either facing the direction of the process (open) or is perpendicular to it (closed). These valves can be either manual or automated.
Butterfly ValveButterfly valves act like a flat disc sitting in a line. When the disc is perpendicular to the line, the valve is closed. When the disc is parallel to the line, the valve is open. These valves are generally used for larger scale pipes, over ball valves, due to the fact that they are considerably less expensive.
Check ValveCheck valves prevent the backflow of a process in a pipe. Wither a spring-loaded disc or a flapper type device located in a pipe accomplishes this.
Safety Relief ValveDesigned to ‘pop’ or relieve at a given set pressure. These valves are used on steam, water, air, and other processes. These valves generally reset or reseat at 20-30% of the set value of to relieve. i.e. – a valve set at 100 psi will not reseat until 70-8- psi.
GaugeA gauge is a pressure indicator that is inserted into a process to show pressure. A bimetal thermometer is the same thing for temperature.
Heat ExchangerHeats up or cools down a process typically by inserting steam or a cooling agent into a tube bundle and passing the process over the bundle.
ActuatorA valve actuator by definition moves something. In our industry, an actuator opens or closes valves or dampers. The most common applications are on ball and butterfly valves.
FilterA filter is used to remove a specific size particulate from a liquid by means of a screen, either fabric or metal.

Terminology in Instrumentation

Flow, Temperature, Pressure, Level, Pumps, and Heat Exchangers


Instrumentation plays a vital role in various industries by accurately measuring and controlling different parameters, such as flow, temperature, pressure, level, among others. In this detailed definition, we will explore each of these terminologies, exploring their significance, applications, and their interaction with instrumentation systems.


Flow refers to the movement of a fluid (liquid or gas) through a system. In instrumentation, flow measurement is essential for maintaining efficiency, safety, and controlling processes.  It enables the accurate determination of the quantity of fluid passing through a given point or within a specific time frame.  Flow meters are commonly used instruments in industries, providing measurements in units such as liters per minute (lpm), gallons per minute (gpm), or cubic meters per hour (m³/h).  These measurements help monitor and regulate flow rates in pipes, ducts, and channels, ensuring optimum performance and preventing issues like blockages or leakage.


Temperature is the measure of the average kinetic energy of particles in a substance. In industrial processes, temperature control is crucial for maintaining product quality, optimizing chemical reactions, and ensuring safe operating conditions.  Temperature sensors, such as thermocouples and resistance temperature detectors (RTDs), are commonly used in instrumentation to measure and monitor temperature changes accurately.  These sensors provide data in units such as Celsius (°C) or Fahrenheit (°F), allowing operators to adjust heating or cooling systems accordingly.


Pressure refers to the force applied per unit area on a surface. In industrial processes, accurate pressure measurement is crucial for safety, process control, and equipment protection.  Pressure transducers, gauges, and switches are widely used instruments to measure and regulate pressure.  They provide readings in units such as pounds per square inch (psi), bar, or pascal (Pa).  Monitoring pressure ensures proper functioning of pumps, motors, and valves while preventing overloads and leaks.


Level measurement refers to determining the height or volume of a substance in a container or vessel. It is critical in industries that involve storage or processing of liquids, solids, or slurries.  Ultrasonic, radar, and capacitance level sensors are commonly used to measure levels accurately.  These sensors provide readings in units such as inches, centimeters, or percentage filled.  Maintaining appropriate levels is key to preventing spills, optimizing storage capacity, and ensuring uninterrupted production.


Pumps are mechanical devices used to transport fluids by increasing their pressure and flow rate.  They are widely used in various industrial processes, including water supply, chemical production, and oil refining.  Pumping systems are integral to instrumentation, as they help maintain desired flow rates, pressure levels, and ensure efficient fluid movement throughout the process.  Instruments such as flow meters and pressure sensors are used in conjunction with pumps to monitor and control their performance.

Heat Exchangers

Heat exchangers are devices used to transfer thermal energy between two or more fluids while keeping them physically separated.  They are commonly used in industries such as HVAC, refrigeration, power generation, and chemical processes.  Instrumentation in heat exchangers involves monitoring temperature differentials, flow rates, and pressure drops across the exchanger to ensure efficient heat transfer.  This data helps operators adjust fluid flow, control temperature, and optimize energy utilization.


Understanding the terminology related to instrumentation, such as flow, temperature, pressure, level, pumps, and heat exchangers.  This is crucial for professionals in various industries.  Incorporating instrumentation into these parameters allows for accurate measurement, control, and optimization of industrial processes.  This leads to improved efficiency, safety, and productivity.  Knowing the application and working principles of these terminologies helps operators make informed decisions.  It also allows you to troubleshoot problems, and maintain optimal operation of systems.

Terminology Definition

Terminology is the study of terms and their use. Terms are words and compound words or multi-word expressions that in specific contexts are given specific meanings—these may deviate from the meanings the same words have in other contexts and in everyday language.

A term is, “a word or expression that has a precise meaning.   In some uses or is peculiar to a science, art, profession, or subject.” 

It is also a discipline that studies, among other things, the development of such terms.  It then studies their interrelationships within a specialized domain.

The difference from lexicography, as it involves the study of concepts, conceptual systems and their labels (terms), whereas lexicography studies words and their meanings.

Terminology is a discipline that systematically studies the “labelling or designating of concepts”.   Particularly to one or more subject fields or domains of human activity.

Finally, through the research and analysis of terms  context.   This is done for the purpose of documenting and promoting consistent usage.

Finally, it can be limited to one or more languages (for example, “multilingual” and “bilingual terminology”), or may have an interdisciplinarity focus on the use of terms in different fields.

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