What is Cv in valve specification?

Cv (flow coefficient) is a dimensionless number that describes the flow capacity of a valve. It is defined as the number of US gallons per minute of water that will flow through the valve with a 1 psi pressure drop at 60°F. For metric systems, the equivalent is Kv (m³/h at 1 bar differential). When sizing a control valve or selecting a valve for a specific flow application, the required Cv is calculated and a valve with a rated Cv equal to or greater than the required value is selected.

What does API 6D mean for valves?

API 6D is the American Petroleum Institute standard for Pipeline and Piping Valves. It specifies design, materials, dimensions, testing, and inspection requirements for gate valves, ball valves, check valves, and plug valves used in pipeline systems for the petroleum and natural gas industries. An API 6D certified valve has been independently tested to meet the standard's full bore, bidirectional sealing, and hydrostatic test requirements.

What is a fire-safe valve certification?

A fire-safe valve has been tested to demonstrate that it maintains a secondary metal-to-metal seal in the event of a fire that destroys the primary soft (elastomeric or PTFE) seats. API 607 is the primary fire-safe testing standard for quarter-turn valves (ball, butterfly, plug), specifying a 30-minute fire test at 750-1000°C followed by water pressure testing. API 6FA is used for pipeline valves. Fire-safe certification is mandatory for hydrocarbon service valves near ignition sources.

What is double block and bleed (DBB) in valve terminology?

Double block and bleed (DBB) refers to a valve or valve arrangement that provides two independent seating surfaces (blocks) and a means to bleed (vent or drain) the cavity between them. Per API 6D, a DBB valve must be able to seal against pressure from both upstream and downstream while the cavity between the seats is vented. This provides positive isolation for maintenance, and is required for critical isolation points in pipelines, metering skids, and process plants.

Industrial Valve Glossary: 113 Terms Explained

A

ActuatorActuation & Automation: A device that moves or controls a valve using an external power source - pneumatic (compressed air), electric (motor), or hydraulic (fluid pressure).
APIStandards & Bodies: American Petroleum Institute.
API 6DStandards & Bodies: The API standard for pipeline and piping valves - gate, globe, check, ball, and plug valves used in oil & gas transmission pipelines.
API 598Standards & Bodies: API standard for valve testing and inspection - shell (body) pressure test, seat leakage test, and backseat test.
API 600Standards & Bodies: API standard for steel gate valves - flanged and butt-welding ends, NPS 1/2" to 60", Class 150 to 2500.
API 602Standards & Bodies: API standard for compact steel gate valves - NPS 1/2" to 4", designed for smaller bore, higher-pressure instrument and process applications.
API 607Standards & Bodies: API standard for fire testing of soft-seated quarter-turn valves.
API 609Standards & Bodies: API standard for butterfly valves - lug- and wafer-style, Category A (concentric/resilient seat) and Category B (double or triple offset/metal seat).
ASMEStandards & Bodies: American Society of Mechanical Engineers.
ASME B16.34Standards & Bodies: The primary ASME standard for pressure-temperature ratings of valves with flanged, threaded, and welding ends.
ASME B16.5Standards & Bodies: ASME standard for pipe flanges and flanged fittings - NPS 1/2" to 24", Class 150 to 2500.

B

BackseatValve Parts: A secondary sealing surface inside the valve body that seats against the stem when the valve is fully open.
Ball ValveValve Types: A quarter-turn valve with a spherical ball as the obturator.
BEP (Best Efficiency Point)Fluid Mechanics: For pump/valve system design, the operating point at which a pump runs at maximum efficiency.
BodyValve Parts: The main pressure-containing shell of the valve.
BonnetValve Parts: The top cover of the valve body that houses the stem and packing/seal arrangement.
BoreFluid Mechanics: The inside diameter of the valve flow passage.
BTO (Breakaway Torque)Actuation & Automation: The torque required to unseat a valve from its fully closed position - the highest torque the actuator must produce.
Butterfly ValveValve Types: A quarter-turn valve using a disc (butterfly) as the obturator.
Butt Weld (BW)Valve Parts: A valve end connection where the valve body ends are welded directly to the pipeline.

C

CavitationFluid Mechanics: A damaging phenomenon in liquid service where the local pressure drops below the liquid's vapour pressure, forming vapour bubbles that then collapse violently as pressure recovers.
Check ValveValve Types: A self-actuating valve that allows flow in one direction only, preventing backflow.
Class (Pressure Class)Standards & Bodies: ASME/ANSI designation for a valve's pressure-temperature capability: Class 150, 300, 600, 900, 1500, 2500, 4500.
Concentric Butterfly ValveValve Types: The simplest butterfly valve design - the stem runs through the centre of the disc and the seat is a resilient (rubber or EPDM) ring.
Control ValveValve Types: A valve used to regulate (modulate) flow, pressure, temperature, or liquid level.
Cv (Flow Coefficient)Fluid Mechanics: The numerical measure of a valve's capacity to pass flow.
Cryogenic ValveService Conditions: A valve designed for service at very low temperatures, typically below −46°C (−50°F).

D

DBB (Double Block and Bleed)Testing & QA: A valve arrangement (or single valve body) providing two independent seating surfaces that isolate from both the upstream and downstream sides, with a bleed/vent port between them to confirm isolation and drain the cavity.
Diaphragm ValveValve Types: A valve where a flexible diaphragm (EPDM, PTFE, or natural rubber) acts as the seating element.
Double-Offset Butterfly ValveValve Types: A butterfly valve with two geometric offsets of the disc stem from the centreline and the pipe bore centreline.
Double-Seated Globe ValveValve Types: A globe valve with two seats and a plug that seats on both simultaneously.
Dual-Plate Check ValveValve Types: A wafer-pattern check valve with two spring-loaded half-disc plates that open with forward flow and snap closed when flow stops.
Duplex Stainless SteelMaterials: A family of stainless steels with a mixed austenitic-ferritic microstructure (≈50/50).

E

E-Body (Eccentric Plug Valve)Valve Types: A plug valve variant where the plug has an eccentric (off-centre) seat that cams in and out during operation, reducing friction and wear.
EPDMMaterials: Ethylene Propylene Diene Monomer rubber.
ESD (Emergency Shutdown) ValveSafety Systems: A safety-instrumented valve that closes automatically in an emergency (detected by gas sensors, fire detectors, or high-pressure switches) to isolate a section of process plant.
ETO (End-to-Open Torque)Actuation & Automation: The torque required to unseat a valve from its fully open position when initiating a closing stroke.
Extended BonnetValve Parts: An elongated bonnet that places the packing/stuffing box away from the extreme temperature of the process fluid.

F

Face-to-Face (F-F)Valve Parts: The dimension from one flange face to the opposite flange face of a valve.
Fail-Closed (FC)Actuation & Automation: An actuated valve that closes automatically on loss of instrument air (pneumatic) or electrical power.
Fail-Open (FO)Actuation & Automation: An actuated valve that opens automatically on loss of instrument air or power.
Fire Safe (Fire Tested)Testing & QA: A valve design tested to maintain acceptable leakage after exposure to a fire event as defined by API 607 or ISO 10497.
FlangeValve Parts: A projecting rim with bolt holes used to connect a valve to piping.
FlashingFluid Mechanics: When liquid flowing through a valve experiences a pressure drop below its vapour pressure and partly vaporises, and the downstream pressure is too low to allow re-condensation.
Floating Ball ValveValve Types: A ball valve where the ball is not fixed to the body - it 'floats' between two seat rings and is pushed against the downstream seat by line pressure to seal.
Fugitive EmissionsTesting & QA: Unintended leakage of process fluid to atmosphere through a valve's stem packing or shaft seal.
Full Bore (Full Port)Fluid Mechanics: A valve where the internal bore diameter equals the nominal pipe bore, resulting in minimal pressure drop (Cv approaches infinity relative to the pipe).

G

Gate ValveValve Types: A multi-turn valve where a flat or wedge-shaped gate (disc) slides perpendicular to the flow to open or close.
Globe ValveValve Types: A multi-turn valve with a disc (plug) that moves perpendicular to the seat.
Graphite PackingMaterials: Stem packing made from flexible graphite, offering wide temperature range (−200°C to +550°C), good chemical resistance, and self-lubricating properties.

H

HandwheelValve Parts: A manual wheel-shaped device attached to the valve stem for opening and closing by hand.
HastelloyMaterials: A family of nickel-based alloys with exceptional corrosion resistance.
HIPPS (High Integrity Pressure Protection System)Safety Systems: A safety instrumented system designed to prevent overpressure in a vessel or pipeline, typically instead of or in addition to a conventional safety relief valve.
HMI (Hand-Manual Interface)Actuation & Automation: Manual override capability on an actuated valve, allowing hand operation when power/air is unavailable.

I

InconelMaterials: A family of nickel-chromium superalloys used for extreme temperature and corrosion environments.
ISO 5208Standards & Bodies: International standard for industrial valves - pressure testing of metallic valves.
ISO 15848Standards & Bodies: ISO standard for measurement, test, and qualification procedures for fugitive emissions from industrial valves.
Isolation ValveValve Types: A valve whose primary purpose is to fully open or fully close to isolate equipment or pipe sections for maintenance or emergencies.

K

Knife Gate ValveValve Types: A gate valve variant with a thin, sharp-edged gate that slices through slurry, pulp, wastewater, or bulk solids.
Kv (Flow Factor)Fluid Mechanics: European equivalent of Cv.

L

LDAR (Leak Detection and Repair)Testing & QA: A regulatory programme (EPA Method 21 in the USA; EU IED in Europe) requiring periodic monitoring of valves, pumps, and flanges for fugitive hydrocarbon emissions, followed by repair when emissions exceed thresholds.
Limit SwitchActuation & Automation: An electrical device mounted on a valve to signal when the valve has reached its fully open or fully closed position.
LNG (Liquefied Natural Gas)Service Conditions: Natural gas cooled to −162°C to liquefy for transport.
Lug Butterfly ValveValve Types: A butterfly valve with threaded inserts (lugs) in the body flange, allowing it to be bolted from both sides.

M

Metal SeatMaterials: A valve seat made from metal (hard-faced Stellite, stainless steel, or Inconel alloy overlay) rather than soft materials (PTFE or elastomer).
MTC (Material Test Certificate)Testing & QA: A document (mill certificate) confirming the chemical composition and mechanical properties (tensile strength, yield strength, elongation, Charpy impact, hardness) of the material used in a valve component, traceable to the heat number.
MOP (Maximum Operating Pressure)Fluid Mechanics: The highest pressure at which a valve will be operated under normal conditions.
Multi-Turn ValveValve Types: A valve that requires multiple rotations of the handwheel or actuator to travel from fully open to fully closed.

N

NACE MR0175Standards & Bodies: NACE International (now AMPP) standard for materials for use in H2S-containing (sour) oil and gas environments, to prevent sulfide stress cracking (SSC).
NBR (Nitrile Rubber)Materials: A synthetic rubber with good resistance to petroleum-based oils and fuels, making it common for valve O-rings and seats in hydrocarbon service.
Needle ValveValve Types: A valve with a slender, tapered needle-shaped plug that mates with a conical seat.
Non-Return Valve (NRV)Valve Types: Another term for check valve - a valve that allows flow in one direction and prevents reverse flow.

O

O-RingMaterials: A circular cross-section elastomeric seal used in valve bore seals, stem seals, and body joints.
OS&Y (Outside Screw and Yoke)Valve Parts: A gate valve design where the stem threads are external to the valve body, outside the packing area.

P

Packing (Stem Packing)Valve Parts: Sealing material compressed around the valve stem in the stuffing box to prevent leakage to atmosphere.
Piggable ValveService Conditions: A valve (usually ball or gate) designed with a full-bore opening and geometry that allows an inspection or cleaning pig to pass through without obstruction.
Pilot-Operated Safety Valve (POSV)Valve Types: A pressure relief valve where a small pilot valve senses system pressure and controls a larger main valve.
Pinch ValveValve Types: A valve that controls flow by pinching a flexible rubber sleeve closed.
Plug ValveValve Types: A quarter-turn valve using a tapered or cylindrical plug with a through-bore as the obturator.
PMI (Positive Material Identification)Testing & QA: Non-destructive testing to verify that valve materials match the specification.
PositionerActuation & Automation: A device mounted on a control valve actuator that receives the controller signal (4–20 mA or HART) and precisely positions the valve to achieve the required Cv.
PRV / PSV (Pressure Relief Valve / Pressure Safety Valve)Valve Types: A valve that automatically opens when system pressure exceeds a set point, relieving excess pressure to protect vessels and pipelines from overpressure failure.
PTFE (Polytetrafluoroethylene)Materials: A fluoropolymer with near-universal chemical resistance and very low friction coefficient.

Q

Quarter-Turn ValveValve Types: A valve that requires only 90° rotation of the operator (handwheel, lever, or actuator) to travel from fully open to fully closed.

R

Raised Face (RF)Valve Parts: The most common flange face type - a raised ring concentric with the bore that concentrates gasket load on a narrow ring area, improving sealing efficiency.
Reduced Bore (Standard Port)Fluid Mechanics: A ball or gate valve where the internal bore is smaller than the nominal pipe size, creating a venturi-like restriction.
Rising StemValve Parts: A valve design where the stem moves upward as the valve opens, providing a visual indication of valve position.
RTJ (Ring Type Joint)Valve Parts: A high-pressure flange face type using a metallic oval or octagonal ring gasket in a machined groove.
RTO (Run-to-Close Torque)Actuation & Automation: The torque required to continue rotating a valve from partway open toward the fully closed position.

S

Safety ValveValve Types: A type of pressure relief valve with a 'pop-action' (snap-open) mechanism that fully opens when set pressure is reached and remains open until pressure drops below the reseat pressure.
SeatValve Parts: The sealing surface inside the valve body against which the disc, ball, gate, or plug closes to achieve shutoff.
SIL (Safety Integrity Level)Safety Systems: A measurement of the performance required for a safety instrumented function (SIF), defined by IEC 61508/61511.
Slab Gate Valve (Through-Conduit)Valve Types: A gate valve where the gate is a flat slab with a bore through it.
Soft SeatMaterials: A valve seat or seat ring made from resilient materials - PTFE, RPTFE (reinforced), DEVLON, or elastomers (EPDM, Viton, NBR).
Solenoid ValveActuation & Automation: An electromechanical valve using a magnetic coil to directly or indirectly control fluid flow.
Sour ServiceService Conditions: Fluid service containing hydrogen sulphide (H2S) at conditions that can cause sulfide stress cracking (SSC) of susceptible materials.
StelliteMaterials: A cobalt-chromium alloy (e.
StrainerValve Types: A device installed upstream of valves, pumps, meters, and instruments to remove particulate from the fluid.
Stuffing BoxValve Parts: The chamber in the valve body that houses and compresses the stem packing (gland packing).
Super DuplexMaterials: High-alloy duplex stainless steels - 2507 (UNS S32750) and Zeron 100 (UNS S32760) - with PREN (Pitting Resistance Equivalent Number) > 40.
Swing Check ValveValve Types: A check valve with a hinged disc (clapper) that swings open on forward flow and swings closed on reverse flow.

T

ThrottlingFluid Mechanics: Partially opening a valve to restrict flow and create a pressure drop, used to regulate flow rate, pressure, or level.
TraceabilityTesting & QA: The ability to trace a valve component back to the original heat of material through documentation - MTCs, PMI, heat numbers stamped on components, and quality records.
TrimValve Parts: The internal components of a valve that are in contact with the process fluid - seat rings, disc/gate/ball, stem, and packing.
Triple-Offset Butterfly Valve (TOBV)Valve Types: The most advanced butterfly valve design with three geometric offsets: two on the disc/stem axis and one on the seat cone angle.
Trunnion Ball ValveValve Types: A ball valve where the ball is fixed (supported) by upper and lower trunnion shafts, independent of pipeline pressure.

U

USP Class VIStandards & Bodies: United States Pharmacopeia standard for materials that contact food, pharmaceutical, or drug products.

V

Viton (FKM)Materials: Fluoroelastomer rubber with excellent resistance to hydrocarbons, fuels, solvents, and elevated temperatures (−20°C to +200°C, short excursions to 250°C).

W

Wafer Butterfly ValveValve Types: A butterfly valve designed to fit between two pipe flanges without its own flange bolting - the pipe bolts pass around the outside of the valve body.
Water HammerFluid Mechanics: A pressure surge caused by the sudden change in fluid velocity in a pipeline - most commonly when a valve closes rapidly and the kinetic energy of the moving fluid converts to a pressure wave.
WedgeValve Parts: The closure element (gate) of a wedge gate valve.

Y

Y-Pattern ValveValve Types: A globe valve (or strainer) design where the flow path is angled at approximately 45° through the body, creating a straighter flow path than a standard T-pattern globe, giving lower pressure drop and Cv.
YokeValve Parts: The structural frame connecting the valve body to the actuator or handwheel.

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