Technical glossary
Definitions of the most common terms used in valves and fluid control.
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A
- Actuator
- Mechanism that automates the motion of a valve from an external signal. The three main types are pneumatic (compressed air), electric (motor) and hydraulic (pressurised oil). Selection depends on required torque, stroking speed and safety requirements.
- ANSI
- American National Standards Institute. The body that coordinates US technical standards; in valve work it is shorthand for the ANSI/ASME B16.5 flange series (classes 150, 300, 600, 900, 1500, 2500).
- API
- American Petroleum Institute. The association that publishes technical standards for the oil and gas industry. Common valve-related standards: API 6A (wellheads), API 6D (pipeline valves), API 600/603 (refinery gate/ball valves), API 526 (relief valves).
- ASME
- American Society of Mechanical Engineers. The US body responsible for many mechanical codes and standards, including ANSI/ASME B16 for flanges and B16.34 for valves, widely referenced on industrial and oil & gas projects.
- ASTM
- American Society for Testing and Materials. US body that maintains standards on materials and testing methods; widely referenced in valve work to specify steels (A105, A216 WCB, A351 CF8M, etc.).
- ATEX
- French acronym (ATmosphères EXplosibles) that names the two European directives regulating equipment and protective systems intended for use in potentially explosive atmospheres. Mandatory marking for valves, instrumentation and electrical items installed in Ex-classified zones.
- AWWA
- American Water Works Association. US body that maintains standards for water treatment and potable / wastewater products; many large-diameter valves are specified under AWWA Cxxx standards.
B
- BHN / HRB / HRC
- Brinell Hardness Number (HB) and Rockwell B / C (HRB / HRC). Three dimensionless hardness scales for steels: the higher the number, the harder the material. Cross-conversion between scales is done with a table.
- Brass
- A copper-zinc alloy widely used in building-services valves thanks to its workability, mechanical properties and corrosion resistance. Properties: good resistance to oxidation; excellent cold machining; readily plated (nickel, zinc, chrome); excellent weldability. EN 12164 and EN 12165 define the brass grades. The current trend in Europe is to move to DZR brasses with improved corrosion resistance and to low- or lead-free brasses.
- BSI
- British Standards Institution. The UK national standards body, responsible for the BS standards and the source of many European EN standards.
C
- Carbon steel
- An iron-carbon alloy. Unlike stainless steels it contains few alloying elements; it is the most-produced steel in the world. Used for valves that require demanding mechanical performance. Properties: low oxidation resistance; better hardness and toughness than grey iron; good mechanical properties; good cold machining. Carbon-steel valves are usually protected with oils and some with epoxy paint to increase oxidation resistance.
- CFM
- Cubic Feet per Minute. The imperial volumetric flow unit commonly used for air and gases. 1 CFM ≈ 1.699 m³/h.
- CI / DI / CS / SS
- Common material acronyms: CI (Cast Iron) = grey cast iron; DI (Ductile Iron) = ductile / nodular iron; CS (Carbon Steel) = carbon steel; SS (Stainless Steel) = stainless steel. See each material's own entry for details.
- Cv / Kv
- Valve flow coefficient. Cv (imperial) is the flow in US gallons/min of 60 °F water that passes through the fully open valve with a 1 psi pressure drop. Kv (metric) is the equivalent in m³/h with a 1 bar drop. Conversion: Kv ≈ 0.865 × Cv.
- CW / CCW
- Clockwise / Counter-clockwise. The direction of rotation of the handwheel or stem when closing the valve. Most valves close clockwise (CW).
- CWP
- Cold Working Pressure. The maximum allowable working pressure under non-shock conditions at ambient temperature (typically 38–52 °C). It is the usual catalogue pressure rating for commercial valves.
D
- DIN
- Deutsches Institut für Normung. German standards institute whose specifications underpin many European (EN) standards. In flanges it refers to the DIN EN 1092 series (PN 6 to PN 100) and metric DN sizing.
- DN
- Short for Nominal Diameter. Indicates the inner diameter through which the fluid flows inside pipes, valves or fittings.
- Double-acting
- Cylinder or actuator configuration in which air (or fluid) is fed alternately to each side of the piston, generating powered motion in both opening and closing directions. Higher speed and torque than single-acting, in exchange for higher consumption.
- Ductile (nodular) iron
- An alloy of iron, carbon and other minor elements with improved hardness and fatigue resistance. Used for valves with medium mechanical demand on non-corrosive fluids and environments. Properties: low oxidation resistance; better hardness than grey iron; better toughness than grey iron; good mechanical properties; excellent cold machining. Ductile-iron valves are also epoxy-coated to improve oxidation resistance.
E
- EPDM
- Ethylene-Propylene-Diene M-class, a synthetic elastomer. Properties: not compatible with hydrocarbons, petroleum or diesel; compatible with drinking water; service temperature −20 °C to 120 °C; high resistance to deformation; good abrasion resistance. Some valves use it as a stem-seal O-ring or flat gasket.
F
- FBE
- Fusion Bonded Epoxy. An epoxy powder coating applied by electrostatic spray and cured with heat; widely used to protect cast-iron and ductile-iron valves against corrosion in water networks.
- FF
- Flat Face. A flange finish in which the gasket bears on the entire flange surface, from the inner diameter to the outer edge. Common on iron, cast-iron and brittle-material flanges.
- FKM
- A fluoropolymer elastomer. Properties: compatible with hydrocarbons, petroleum and diesel; compatible with drinking water; service temperature −20 °C to 180 °C; high resistance to deformation; good resistance to high temperatures; suitable as a sealing element for solar-thermal valves. Some valves use it as a stem-seal O-ring or flat gasket.
- Flame arrester
- Passive device that stops a flame from propagating along a pipe carrying flammable gas or vapour. Works through a bundle of very narrow channels (crimped meshes, plates) that conduct heat away from the flame front, dropping it below the ignition temperature.
- Flanges
- Bolted-disc piping connection used throughout industrial pipework. Allows rapid assembly and disassembly. Identified by standard (ANSI, DIN, JIS), pressure class (PN, Class) and face type (RF, FF, RTJ) depending on the gasket.
- FM
- Factory Mutual. US organisation that certifies products for fire and other industrial-safety applications; the FM Approved mark is common on firefighting valves.
- Full bore
- A valve is considered Full Bore when the fluid passage equals its DN (Nominal Diameter). Defined by UNE-EN 13828.
G
- GPM
- Gallons Per Minute. The imperial volumetric flow unit used in US catalogues. 1 GPM (US) ≈ 0.227 m³/h.
- Grey cast iron
- An alloy of iron, carbon and other minor elements. Used for valves with low mechanical demand on non-corrosive fluids and environments. Properties: low oxidation resistance; low hardness; medium brittleness; good mechanical properties; excellent cold machining. Grey-iron valves are typically epoxy-coated to substantially improve oxidation resistance.
H
- HW
- Handwheel. A wheel-shaped operating device grasped with one or both hands to turn the stem or shaft of a valve. The most common manual actuator on gate and globe valves.
I
- IBBM
- Iron Body, Bronze Mounted. A classic valve build with iron body and bonnet and bronze trim (seats, stem, bushings); still common on gate and globe valves for water service.
- ID / OD
- Inside Diameter / Outside Diameter. ID is the nominal or actual distance between the inner walls of an annular body (pipe, valve seat); OD is the outer diameter, commonly used to size stainless-steel piping and threaded connections.
- IP (ingress protection)
- Standardised coding system (IEC 60529) that states the degree of protection an enclosure offers against ingress of solid bodies (first digit, 0–6) and water (second digit, 0–9). Example: IP65 = dust-tight and protected against low-pressure water jets.
- Iron
- A common metal that is brittle and has poor hardness and oxidation resistance. In valve manufacturing it is usually galvanised (a chemical treatment) to improve its resistance to oxidation.
- ISO
- International Organization for Standardization. The worldwide federation that develops and publishes international standards, including the dimensional and performance standards applied to pipes, flanges and valves (DN/PN).
J
- JIS
- Japan Industrial Standard. Japan's national standards system; among other things it specifies JIS flanges, a common alternative to EN/ANSI flanges on Asian projects.
L
- Lug
- Wafer-body variant with threaded lugs that bolt to one pipe flange — allowing the downstream side to be removed without draining the whole line. Common on butterfly valves installed as end-of-line shut-off valves.
M
- MAWP
- Maximum Allowable Working Pressure. The maximum pressure (bar or psi) at which a valve is designed to operate. The value drops with temperature following the pressure–temperature curves.
- MJ
- Mechanical Joint. A bolted joint style common on ductile-iron water valves and piping: bolting compresses an elastomer gasket between a follower flange and the pipe spigot to seal.
- MOV
- Motor-Operated Valve. A valve fitted with a motorised electric actuator that opens and closes it remotely. The most common arrangement for valves driven from a control system.
- MSS
- Manufacturers Standardization Society of the Valve and Fittings Industry. Industry body that publishes technical standards for valves, fittings and materials (SP series).
N
- NACE
- National Association of Corrosion Engineers (now AMPP). Publishes corrosion-related standards, including the reference materials specifications for sour-gas service (MR0175 / MR0103).
- NBR
- Nitrile Butadiene Rubber. A rubber-derived elastomer. Properties: compatible with hydrocarbons, petroleum and diesel; compatible with drinking water; service temperature −20 °C to 80 °C; high resistance to deformation; good abrasion resistance. Some valves use it as a stem-seal O-ring or flat gasket.
- NDE
- Non-Destructive Examination. A family of tests — radiography, ultrasonic, liquid penetrant, magnetic particle — that verify a component's integrity without damaging it. Required on critical-service valves.
- NEMA
- National Electrical Manufacturers Association. Defines enclosure protection codes (NEMA 4, 4X, 7, etc.) that broadly correspond to the IEC IP ratings used on electric actuators.
- NFPA
- National Fire Protection Association. Maintains standards aimed at minimising fire risk in buildings, processes and installations; NFPA codes typically apply to firefighting networks.
- NPS
- Nominal Pipe Size. The dimensionless designation of pipe size used in ANSI/ASME standards, equivalent to the European DN (e.g. NPS 4 ≈ DN 100).
- NPT
- National Pipe Thread Taper. The American tapered thread for pressure connections defined in ASME B1.20.1; very common on US-origin threaded valves and fittings.
O
- Operating torque
- The force, measured in Nm, required to open or close the valve. Its value is critical for correctly sizing an actuator. Operating conditions — pressure, temperature, differential pressure, fluid density and viscosity — can change the torque significantly, so a safety margin of at least 30 % must be allowed.
- OS&Y
- Outside Screw and Yoke. A valve design — usually gate or globe — in which the stem thread sits above the packing gland on a yoke, giving a visual indication of valve position. Common on fire-protection systems.
P
- PN
- Short for Nominal Pressure. Indicates the maximum internal working pressure at ambient temperature and atmospheric external pressure. The working-pressure limit is a curve that decreases as temperature rises. Selecting a valve correctly starts by establishing the temperature and pressure conditions and checking that the operating point stays within the valve's mechanical envelope.
- Pressure loss
- A drop in the fluid's dynamic energy caused by friction against the walls and between the fluid's own particles. Sudden changes of direction or diameter increase pressure loss significantly.
- Pressure-vacuum relief valve (PVRV)
- Combined valve that protects an atmospheric storage tank against two failure modes: overpressure from filling or thermal expansion and vacuum from draining or thermal contraction. Common on hydrocarbon and chemical tanks to minimise emissions and prevent collapse.
- PSI / PSIA / PSIG
- Pounds per Square Inch. The imperial pressure unit: 1 bar ≈ 14.5 psi. The suffix «A» (PSIA) marks absolute pressure (referenced to vacuum), while «G» (PSIG) marks gauge pressure (referenced to the atmosphere, ≈ 14.7 psi).
- PTFE
- Polytetrafluoroethylene, a synthetic elastomer. Properties: compatible with most chemicals; compatible with drinking water; service temperature −270 °C to 280 °C; good resistance both near absolute zero and at high temperatures; the lowest friction coefficient of any known material; suitable as a sealing element for solar-thermal valves; easy to machine; can be blended with graphite or glass fibre to improve its mechanical properties. Some valves use it as a flat stem seal.
- PVC
- Polyvinyl Chloride. A common thermoplastic used in valves and pipes for non-aggressive fluids at moderate temperature; low cost and excellent chemical resistance to water and many common chemicals.
R
- Reduced bore
- A valve is considered Reduced Bore when the fluid passage is one size smaller than its DN (Nominal Diameter). Defined by UNE-EN 13828.
- RF
- Raised Face. A flange finish in which the gasket-contact area is slightly raised above the rest of the face; this concentrates the bolt load on the gasket and improves sealing. It is the standard finish on ANSI flanges.
- RJ
- Ring-Type Joint. A flange finish in which sealing relies on two narrow metal-to-metal contact lines on a metal ring set into a groove machined into each flange face. Common in high-pressure and oil & gas service.
- RPM
- Revolutions Per Minute. The rotational-speed unit commonly used for pumps, motors and actuators.
- Rupture disc
- Non-reclosing safety device built around a calibrated metal membrane that bursts at a preset overpressure, rapidly venting the fluid and protecting the equipment. Often used as a back-up or complement to spring-loaded safety valves.
S
- SCADA
- Supervisory Control and Data Acquisition. A computer system that supervises remote processes — including motorised valves and sensors — and centralises signals and control in a control room.
- Single-acting
- Configuration in which air or fluid acts on one side of the piston only. The return motion is provided by a spring (fail-safe) or by gravity. Typical of actuators that need a defined safety position on loss of air.
- Stainless steel
- Two grades are mainly used for valves under high mechanical loads and corrosive fluids or environments: A304/A304L — austenitic stainless with good corrosion resistance — and A316/A316L — austenitic stainless with better resistance thanks to molybdenum. Properties: excellent oxidation resistance; good cold machining; good weldability in the low-carbon "L" versions (A304L and A316L); very good mechanical properties with high toughness. Mechanical performance varies with cooling rate and heat treatments. Described by EN 10088.
T
- Tightness
- The condition that no fluid leaks through the valve when closed, nor through any other point (stem, body-bonnet joint, etc.).
U
- UL
- Underwriters Laboratories. US organisation that certifies safety products and materials intended for fire-protection applications (FM/UL valves for firefighting).
W
- Wafer
- Flangeless valve body style designed to be sandwiched between two pipe flanges using through-bolts. Lightweight and economical, typical of butterfly, check and ball valves for low-demand service.
- Water hammer
- A spike in pressure that occurs in hydraulic installations when the fluid flow is shut off abruptly. It is dangerous because the pressures can rise well above the nominal rating of the components and burst pipes, fittings and/or valves. It is mitigated by slowing down valve closure or by fitting a device that absorbs the excess pressure (expansion vessels, water-hammer arresters).
- WOG
- Water-Oil-Gas. A legacy pressure designation still used on small low-rating valves; it states the maximum working pressure at ambient temperature (32–100 °F) for water, oil or gas. Equivalent to the CWP.
- WP
- Working Pressure. The pressure under normal service; synonymous with operating pressure. It must not exceed the MAWP at the process temperature.