A ferrule is the metal sealing ring inside a compression tube fitting; tightening the nut swages it onto the tube's outside diameter to form a leak-tight, gas-tight mechanical seal. Crestflo supplies single and double ferrules in stainless, high-nickel alloys and titanium, hardened or non-hardened.

NPT (National Pipe Taper) is a US tapered pipe thread that seals on the thread flanks, defined by ASME B1.20.1; NPTF (Dryseal) is a tighter-tolerance variant that can seal with less sealant.

PREN (pitting resistance equivalent number) is a calculated index of an alloy's resistance to chloride pitting, PREN = Cr + 3.3 x Mo + 16 x N. A higher PREN indicates greater pitting resistance, and is the basis for stepping up from 316 to 904L, duplex or super-duplex.

Resources

Instrumentation Fitting & Valve Glossary

Q: What is another name for a ferrule?

In fluid systems it is also called a compression ring, a sleeve, or in some markets an olive. It is distinct from a wire/electrical ferrule or a golf-club ferrule; this glossary covers the fluid-system compression ferrule only.

Q: What is the difference between a ferrule and a crimp?

A ferrule seals by being compressed (swaged) onto a tube by a threaded nut and remains a serviceable, re-makeable joint in a tube fitting; a crimp is a permanently deformed connection common in wiring and hose ends. The two are not interchangeable.

Q: What does a ferrule look like?

It is a small precision metal ring, or in a two-piece design a front and back ferrule, that slips over the tube and sits inside the fitting nut. After make-up it leaves a visible swage mark where it has gripped the tube outside diameter.

Q: What is the difference between a single-ferrule and a double-ferrule fitting?

A single-ferrule fitting uses one ring to both seal and grip; a double-ferrule fitting uses a front ferrule for the seal and a back ferrule for tube grip, which helps under vibration and pressure cycling.

Q: What is a needle valve versus a ball valve?

A needle valve throttles flow precisely with a tapered stem (an instrumentation valve, not a carburetor part); a ball valve gives fast quarter-turn on/off through a bored ball (an instrumentation valve, not a plumbing valve).

Q: What is double block and bleed (DBB)?

Double block and bleed provides two isolation points in series with a bleed between them, so a line can be positively isolated and the isolation verified by venting the cavity. Crestflo DBB valves are designed to ASME B16.34.

Q: What is a mill test certificate (MTC)?

An MTC is an EN 10204 document certifying a material's chemistry and mechanical properties: a 3.1 certificate is issued by the manufacturer, a 3.2 is countersigned by an independent inspector. Crestflo provides 3.1 as standard and 3.2 on request, with the heat number marked on every part.

Instrumentation Fitting & Valve Glossary

Reviewed by the Crestflo Engineering Team

This glossary covers every fitting, valve, thread, alloy, standard and quality term used across instrumentation and process fluid-system components, explained in plain English, with each term linked to its full specification page. The audience: engineers, buyers, distributors and field technicians who scope, source and install these parts. Each definition leads with the answer and stays short on purpose. Complete vocabulary coverage is the point here; ratings, sizes and ordering detail live on the linked spec page. Start with the anchor term below, browse by category, or jump straight to an acronym.

Scope: every term in this glossary refers to an instrumentation or process fluid-system component. Take the ferrule, for instance: it's a fluid-system compression ferrule, the metal sealing ring inside a tube fitting, not a wire or electrical ferrule, and not the kind you'd find on a golf club or in dentistry. Needle valve, in this context, means an instrumentation flow-control valve rather than a carburetor part. A ball valve is an instrumentation valve, not something out of a plumbing supply catalog. Manifold refers to a valve manifold here, not an exhaust manifold or a PEX manifold. And a compression fitting is a stainless or alloy fitting built for instrumentation work, not a copper fitting for household plumbing.

What is a ferrule? The anchor definition

A ferrule is the metal sealing ring inside a compression tube fitting. When you tighten the nut, the ferrule swages onto the tube's outside diameter (OD), forming a leak-tight, gas-tight mechanical seal. In fluid systems, people also call it a compression ring, a sleeve, or, in some markets, an olive.

What is a ferrule used for? It turns nut torque into a controlled radial grip and seal on the tube. That's what lets the joint hold pressure and shrug off vibration and thermal cycling, no welding or soldering required.

What does a ferrule look like? Picture a small precision ring, or in a two-piece design, a front and back ferrule, fitted over the tube and inside the fitting nut. Once it's made up, it leaves a visible swage mark on the tube OD.

What is the difference between a ferrule and a crimp? A ferrule gets compressed, or swaged, onto the tube by a threaded nut, and the joint stays serviceable; you can remake it later. A crimp, by contrast, is a permanent deformation, the kind you see in wiring and hose ends. This glossary deals only with the fluid-system ferrule.

Property	Value
What it is	Compression sealing ring inside a tube fitting
Also known as	Compression ring, sleeve, olive, twin-ferrule (double)
Function	Swages onto the tube OD to form a leak-tight, gas-tight seal
Common forms	Single ferrule; front + back (double) ferrule
Crestflo options	Single & double ferrules; hardened or non-hardened; stainless, high-nickel alloy & titanium
NOT	A wire/electrical, golf-club or dental ferrule

Want the full rundown on the part itself? Check the <a href="https://crestflousa.com/products/tube-fittings/ferrules/">tube-fitting ferrules</a> page. And if you're weighing one-piece against two-piece designs, the <a href="https://crestflousa.com/resources/single-vs-double-ferrule/">single vs double ferrule</a> page walks through that choice.

Also known as: what this instrumentation glossary is called

People land on a reference like this from all kinds of search terms. Some type in an instrumentation fittings glossary, others want a tube fitting glossary or tube fitting terminology, and plenty search for an instrumentation valve glossary. You'll also see it called a fluid-system components dictionary, a set of fitting and valve definitions, a process instrumentation vocabulary, or just a "what is a…" reference for fittings and valves. No matter which phrase shows up on a drawing or a purchase order, the definitions below stick to the standard published designations: UNS and Werkstoff numbers for alloys, ASTM/ASME/ISO/DIN/NACE/API numbers for standards, and the trade abbreviations engineers actually type (NRV, DBB, CWP, PREN, MTC, EP).

Every term links to its owner page, <a href="https://crestflousa.com/products/tube-fittings/">tube fittings</a>, <a href="https://crestflousa.com/products/instrumentation-valves/">instrumentation valves</a>, <a href="https://crestflousa.com/materials/">materials</a>, <a href="https://crestflousa.com/standards/">standards</a>, and the <a href="https://crestflousa.com/resources/">resource guides</a>. A definition is never more than a click from the full spec or comparison.

Fittings & connection terms: ferrule, compression & tube-fitting definitions

The core vocabulary of mechanical, weld and quick connections. Each term links to its product or how-to page.

Compression fitting / compression tube fitting: A mechanical tube fitting that seals and grips a tube by compressing one or more ferrules onto the tube OD as the nut is tightened, no flaring, brazing or welding. In instrumentation these are stainless or alloy, not copper plumbing fittings. See: stainless tube fittings.
Twin-ferrule / double-ferrule fitting: A compression fitting using two ferrules, a front ferrule that seals and a back ferrule that grips the tube, for vibration and pressure performance. See: compression tube fittings.
Single-ferrule fitting: A compression fitting that uses one ferrule to both seal and grip; simpler and fewer parts than a two-piece design. See: single-ferrule tube fittings.
Ferrule-less / gaugeable fitting: A compression-style fitting without conventional ferrules, using an alternative gripping element while remaining gaugeable at make-up. See: ferrule-less tube fittings.
Front ferrule / back ferrule: In a two-piece set, the front ferrule forms the primary seal against the fitting body while the back ferrule bites the tube for grip. See: tube-fitting ferrules.
Hardened vs non-hardened ferrule: A case-hardened back ferrule grips hard or heavy-wall tube better; non-hardened suits softer alloys. See: hardened vs non-hardened ferrules.
Instrumentation tube fitting: The general class of precision fittings used to connect small-bore instrument tubing to gauges, valves and process taps. See: tube fittings.
Bite-type / DIN 2353 fitting: A cutting-ring compression fitting to DIN 2353 where a ring "bites" into the tube; common on hydraulic lines. See: DIN 2353 fittings.
Flare fitting (37° JIC / 45° SAE): A fitting that seals on a cone-shaped flared tube end, 37° for JIC, 45° for SAE automotive/refrigeration. See: flare fittings, 37° JIC, 45° SAE.
Cone-and-thread / high-pressure fitting: A high-pressure connection where a coned, threaded tube end seals in a matching gland for extreme-pressure service. See: cone-and-thread fittings.
Face-seal fitting (VCR / VCO): A high-purity or high-integrity fitting that seals on a flat gasket face, VCR uses a metal gasket, VCO an O-ring. See: face-seal fittings, VCR face-seal fittings, VCO O-ring face seal.
Quick-connect / quick-disconnect: A coupling that connects or disconnects a line by hand without tools, often with a shut-off check. See: quick-connect fittings.
Push-to-connect / push-in / push-on fitting: A fitting that grips and seals tube on insertion via an internal collet and O-ring; released by a collar. Also called a push-on fitting where the tube pushes on to the stem. See: push-to-connect fittings.
Orbital-weld, socket-weld & butt-weld ends: Welded connection types: orbital automated tube welds for high purity; socket-weld inserts the tube into a recess; butt-weld joins ends edge-to-edge. See: orbital-weld fitting, socket-weld, butt-weld.
Union, connector, elbow, tee, cross, reducer, adapter: Standard flow-path geometries: a union joins two tubes in line; connectors terminate to a thread; elbows turn 90°/45°; tees and crosses branch; reducers change size; adapters change end type. See: union, elbow, tee, cross, reducer, adapter.
Bulkhead union & port connector: A bulkhead union mounts through a panel and seals both sides; a port connector joins a fitting body to a threaded port. See: bulkhead union, port connector.
Cap, plug, male & female connector, weld connector, nut-and-ferrule: Terminations and thread transitions: a cap closes a tube end, a plug closes a fitting port; male/female connectors adapt tube to external/internal thread; a weld connector adapts to a weld end; nut-and-ferrule is the sealing hardware set. See: cap, plug, male connector, female connector, weld connector, nut-and-ferrule.
Fitting body, nut, tube stub, pull-up & gauging: Installation vocabulary: the body houses the ferrules; the nut drives them; the tube stub is the inserted tube length; pull-up is the tightening (typically 1¼ turns from finger-tight on many designs); gauging uses a gap gauge to verify correct make-up. See: ferrule installation and gauging.

Thread & connection-standard terms: NPT, BSP, JIC & metric definitions

Thread types aren't all the same. Profile, taper, and where they seal all set them apart. Each one links to its own product or comparison page.

NPT (National Pipe Taper): A US tapered pipe thread that seals on the thread flanks, typically with sealant; defined by ASME B1.20.1. See: NPT tube fittings, ASME B1.20.1.
NPTF (Dryseal): A tighter-tolerance NPT variant whose crests and roots interfere to seal without (or with less) sealant. See: NPTF fittings, NPT vs NPTF.
BSPT / BSPP: British Standard Pipe threads: BSPT is tapered and seals on the threads; BSPP is parallel and seals on a face or bonded washer. See: BSPT, BSPP, BSPP vs BSPT, NPT vs BSP.
ISO parallel (G) thread: A parallel pipe thread (G designation) that seals on an external face or O-ring rather than the threads. See: ISO-parallel fittings.
Metric & imperial/fractional threads: Sizing systems for tube and thread, metric in millimeters, imperial in fractional inches; instrumentation fittings are made in both. See: metric fittings, imperial-fractional, metric vs imperial tube fittings.
JIC-37 & SAE-ORB (O-ring boss): JIC-37 is a 37° flare thread; SAE-ORB seals with an O-ring seated in a straight-thread boss. See: JIC-37, SAE-ORB, JIC vs ORB, JIC vs DIN 2353.
Tube OD & fitting size: Instrumentation fittings are specified by tube outside diameter (OD), not nominal bore; size charts cross imperial and metric. See: tube OD, tube-fitting size chart, thread identification guide.

Valve terms: needle, ball, check, manifold & double block and bleed definitions

Instrumentation valves get defined by how they operate. Here, a needle valve means an instrumentation flow-control valve, not a carburetor part, and a ball valve means an instrumentation valve, not the kind used in plumbing.

Needle valve: A valve that throttles flow precisely by advancing a tapered stem into a matching seat; used for metering, isolation and gauge service. See: needle valve, needle vs ball valve.
Ball valve (3-way, L-port, T-port, trunnion, full-port, CWP): A quarter-turn valve using a bored ball for fast on/off; multi-port (L/T) balls divert flow, trunnion designs support the ball for higher pressure, and CWP denotes the cold working pressure rating. See: ball valve, 3-way, L-port, T-port, trunnion, CWP ball valve.
Check valve / NRV (non-return valve): A valve that permits flow in one direction and closes on reverse flow; NRV is the common abbreviation, and a pneumatic check version suits gas/air lines. See: check valve, NRV, pneumatic check valve.
Bleed valve & purge valve: A bleed valve safely vents trapped pressure or drains a cavity; a purge valve clears a line or instrument of process fluid or air. See: bleed valve, purge valve.
Gauge / root valve: The primary isolation valve at the process tap ("root") that isolates an instrument or gauge for service. See: gauge root valve.
Metering & flow-control valve: Fine-adjustment valves that regulate a precise flow rate, often with a vernier or non-rotating stem. See: metering valve, flow-control valve.
Plug, toggle, angle & quick-exhaust valve: A plug valve uses a tapered/cylindrical plug for on-off; a toggle valve is lever-actuated for rapid on-off; an angle valve turns flow 90°; a quick-exhaust valve rapidly vents an actuator. See: plug valve, toggle valve, angle valve, quick-exhaust valve.
Relief valve: A valve that opens automatically at a set pressure to protect equipment from overpressure, then reseats. See: relief valve.
Excess-flow valve: A valve that senses flow rate and shuts off automatically when flow exceeds a preset limit, for example on a line break or hose rupture, then resets once the pressure equalises. See: instrumentation valves.
Packless valve: bellows & diaphragm: Stem-sealed-without-packing valves, a welded bellows or a diaphragm isolates the stem, minimising fugitive emissions for high-purity or hazardous media. A bellows or diaphragm stem seal is the basis of a zero-leak valve configuration for hazardous or high-purity duty. See: bellows valve, diaphragm valve.
Manifold valve (2-, 3- & 5-valve): An integral block combining the block, equalise and vent valves needed to isolate and calibrate a pressure or differential-pressure transmitter, 2-valve for direct-mount gauges, 3- and 5-valve for DP transmitters. See: 2-valve, 3-valve, 5-valve manifold, 2 vs 3 vs 5-valve.
Monoflange valve: A compact single-flange assembly that replaces a conventional flanged isolation train, combining block and bleed (and often a needle) in one body. See: monoflange valve, monoflange vs manifold.
Double block and bleed (DBB): An arrangement providing two isolation (block) points with a bleed between them, so the line can be positively isolated and verified; designed to ASME B16.34. See: double block and bleed valve, DBB vs monoflange.

Regulator & accessory terms: thermowell, snubber, filter & syphon definitions

Pressure-control and instrument-protection components that surround the valve and fitting set.

Pressure regulator (single-stage, dual-stage, back-pressure, changeover, cylinder, high-purity, high-pressure): A device that reduces and holds a stable downstream (or, for back-pressure, upstream) pressure; dual-stage smooths supply drop, changeover switches between cylinders, and high-purity versions suit analytical gas. See: pressure regulators, single-stage, dual-stage, back-pressure, changeover, cylinder, high-purity, high-pressure.
Thermowell: A closed-end bar-stock sheath that protects a temperature sensor from the process while allowing removal without breaching the line. See: thermowells.
Syphon (pigtail / coil): A looped fitting that traps a liquid seal to protect a pressure gauge from steam or hot media. See: syphons.
Condensate pot & air-distribution manifold: A condensate pot collects condensate on steam-service DP lines; an air-distribution manifold splits an instrument-air supply to multiple loads. See: condensate pots, air-distribution manifolds.
Snubber & gauge saver: A snubber damps pressure pulsation and spikes to protect a gauge; a gauge saver shuts off automatically on overpressure. See: snubbers, gauge savers.
Filter (inline / tee-type): An in-line strainer that removes particulate to protect downstream instruments and valve seats. See: filters, inline filters, tee-type filters.
Flexible hose assembly: A flexible metal or PTFE-lined hose with end fittings for movement, vibration isolation or misalignment. See: flexible hose assemblies.
Sampling cylinder & grab sampling system: A sampling cylinder captures a pressurized process sample for lab analysis; a grab sampling system does so safely as a closed loop. See: sampling cylinders, grab sampling systems.
Tube clamp, flushing ring, vent protector, spare ferrules & nuts, tube installation tool: Support and service hardware: clamps route and secure tubing; a flushing ring lets a diaphragm seal be cleaned in place; a vent protector shields a relief vent; spare ferrules/nuts and installation tools support field make-up. See: tube clamps, flushing rings, vent protectors, spare ferrules & nuts, tube installation tools.

Material & metallurgy terms: stainless, duplex, nickel alloys, UNS, PREN & passivation

Crestflo covers each grade in broad strokes and supplies it in instrumentation form: fittings, valves, tubing. Not bar, sheet, plate or mill product.

Stainless steel 304/304L, 316/316L, 904L: Austenitic stainless grades: 304/304L is the general grade, 316/316L adds molybdenum for chloride resistance, and 904L is a high-molybdenum super-austenitic. See: 316/316L, 304/304L, 904L.
Duplex 2205 & Super Duplex 2507: Two-phase austenitic-ferritic stainless steels combining high strength with strong chloride pitting resistance; 2507 (Zeron 100 class) is the higher-alloy super-duplex. See: Duplex 2205, Super Duplex 2507, duplex vs super duplex.
254 SMO, AL-6XN & Alloy 20: 6-molybdenum super-austenitic stainless grades (254 SMO, AL-6XN) for seawater and high chlorides, and Alloy 20 for strong reducing acids such as sulfuric. See: 254 SMO, AL-6XN, Alloy 20.
High-nickel alloys & CRA (Inconel, Incoloy, Monel, Hastelloy, Nickel 200/201): Corrosion-resistant alloys (CRA) for the most aggressive service: Inconel 600/601/625/718/825 and Incoloy 800/800H for heat and oxidation, Monel 400/K500 for seawater and HF, Hastelloy C-276/C-22/B-2/B-3/X for wet chlorides and acids, and commercially pure Nickel 200/201. See: Inconel 625, Monel 400, Hastelloy C-276, Nickel 200/201.
Titanium Grade 2: A light, commercially pure titanium with excellent resistance to seawater and oxidising chlorides. See: titanium Gr2, titanium vs stainless.
UNS number & Werkstoff number: Standard alloy identifiers, UNS is the Unified Numbering System (e.g. S31600 for 316) and Werkstoff is the European material number (e.g. 1.4401), used to specify a grade unambiguously across drawings and mill certificates.
Austenitic & CRA (corrosion-resistant alloy): Austenitic denotes the face-centered-cubic stainless structure (non-magnetic, tough, weldable); CRA is the umbrella term for alloys selected primarily for corrosion resistance.
PREN (pitting resistance equivalent number): A calculated index of an alloy's resistance to chloride pitting, PREN = Cr + 3.3×Mo + 16×N; higher values indicate greater pitting resistance. See: PREN comparison table, corrosion × alloy matrix.
Passivation: A chemical treatment (typically nitric or citric acid) that removes free iron and enriches the chromium-oxide layer on stainless steel to restore corrosion resistance after machining. Finishing is available to the applicable standard, customizable to requirement.
Electropolishing (EP) & surface finish (Ra): Electropolishing electrochemically removes a thin surface layer to smooth and brighten the metal; Ra (roughness average) quantifies the resulting surface finish. Standard UHP targets (for example ≤10–15 µin Ra) are specified per SEMI/ASME BPE, state your target Ra on the RFQ. See: electropolished tubing.
Heat treatment, silver anti-galling plating & hardened ferrule: Heat treatment (solution annealing, or case-hardening of a back ferrule) sets the alloy's metallurgical condition and surface hardness; silver plating on threads or ferrules reduces galling in stainless and nickel alloys, and a case-hardened ferrule improves tube grip. Available to requirement. See: hardened vs non-hardened ferrules.

Standards, certification & QA terms: F1387, NACE MR0175, MTC & ASME definitions

Each entry gives the one-line scope and links to the full standard page. Crestflo holds the standard approvals that apply to each product type, and it's certified to ISO 9001 / 14001 / 45001 and PED.

ASTM F1387: The performance-qualification standard for mechanically attached (compression tube) fittings, the basis for demonstrating drop-in interchange of fittings. Applies to fittings, not valves. See: ASTM F1387.
NACE MR0175 / ISO 15156 & MR0103: Standards governing metallic materials for resistance to sulfide stress cracking in sour (H₂S) service, MR0175/ISO 15156 for oil-and-gas production, MR0103 for refining. See: NACE MR0175, ISO 15156, NACE MR0103, sour-service selection.
EN 10204 MTC (mill test certificate) 3.1 / 3.2: The document certifying a material's chemistry and mechanical properties: a 3.1 certificate is issued by the manufacturer, a 3.2 is countersigned by an independent inspector. Crestflo provides 3.1 as standard and 3.2 on request. See: EN 10204 MTC.
Heat number & traceability: The heat (melt lot) number links a part back to its certified material; Crestflo marks the heat number on every part for full traceability. See: traceability.
ASME B16.34, B16.11, B1.20.1, B31.3, BPE: Core ASME references: B16.34 (valve pressure-temperature design), B16.11 (forged fittings), B1.20.1 (NPT threads), B31.3 (process piping design), and BPE (bioprocessing equipment hygienic design). See: B16.34, B16.11, B1.20.1, B31.3, ASME BPE.
ASTM material specs (A269, A213, A312, A479, A276, A182, A789, A790): Product-form specifications for stainless and alloy tube, pipe, bar and forgings used in instrumentation. See: A269, A213, A312, A479, A276, A182, A789, A790.
API valve standards (598, 602, 607, 6D, 6FA) & ISO 15848: API test and design standards for valve inspection, testing and fire-safe qualification; ISO 15848 covers fugitive-emission testing. Valves qualify to ASME B16.34 / API, not ASTM F1387. See: API 598, API 602, API 607, API 6D, API 6FA, ISO 15848.
ISO 9001 / 14001 / 45001 & PED: Management-system and directive certifications: quality (9001), environmental (14001), occupational health & safety (45001), and the EU Pressure Equipment Directive (PED). Crestflo is ISO 9001 / 14001 / 45001 & PED certified.
PMI & NDT: Positive Material Identification (PMI) verifies alloy grade by spectroscopy; Non-Destructive Testing (NDT) checks integrity without damaging the part. Crestflo performs PMI and in-house NDT, with destructive testing at ISO/IEC 17025-accredited labs. See: quality & traceability.
Pressure & leak testing (hydrostatic, proof, burst, impulse, seat & shell): Verification tests: hydrostatic/proof confirms the working rating, burst finds the ultimate limit, hydraulic impulse (cyclic pressure) testing proves fatigue endurance, and seat & shell leak tests confirm valve tightness (100% on manifolds). See: testing & inspection.
Oxygen cleaning (ASTM G93 / CGA G4.1), 3-A sanitary & NORSOK M-630/M-650: Cleanliness and qualification standards: oxygen-service cleaning to ASTM G93 / CGA G4.1, hygienic design to 3-A, and material qualification to NORSOK M-630/M-650 for offshore. See: ASTM G93, CGA G4.1, 3-A sanitary, NORSOK M-630, NORSOK M-650.
TAA / country of origin: The Trade Agreements Act governs country-of-origin requirements on certain US procurements. Crestflo's standard product is of Indian origin; US or European melt is available on request with full material traceability. See: US-origin compliance.

Pressure, temperature & flow terms: CWP, MAWP, Cv & cryogenic definitions

Working pressure / CWP (cold working pressure): The maximum pressure a component is rated for at ambient temperature; CWP is the standard non-shock rating at room temperature. See: CWP ball valve.
MAWP, proof & burst pressure: MAWP is the maximum allowable working pressure of the assembly in service; proof pressure is a non-damaging overpressure verification; burst pressure is the pressure at ultimate failure, always well above the working rating.
Pressure–temperature derating: The reduction in allowable pressure as service temperature rises, following the material's allowable-stress curve. See: pressure–temperature derating.
Cv (flow coefficient): A dimensionless-referenced flow capacity, the US gallons per minute of water at 60°F that pass through a valve at 1 psi drop; higher Cv means greater flow capacity.
Cryogenic & LNG service: Very-low-temperature service (for example liquefied natural gas) requiring alloys that stay tough at cryogenic temperatures, such as austenitic stainless. See: cryogenic / LNG selection.
High-purity / UHP & oxygen service (O₂-clean): Ultra-high-purity (UHP) service demands electropolished, particle-free surfaces; oxygen service requires hydrocarbon-free "O₂-clean" components to avoid ignition. See: high-purity / semiconductor selection.

Instrumentation abbreviations & acronyms: what NRV, DBB, CWP & PREN stand for

The trade shorthand shows up on drawings and RFQs. Spell it out, then route it to its definition or the page that owns it.

Abbreviation	Stands for	Reference
NRV	Non-return valve (check valve)	check valve
DBB	Double block and bleed	DBB valve
CWP	Cold working pressure	CWP ball valve
MAWP	Maximum allowable working pressure	pressure & flow terms
Cv	Flow coefficient	pressure & flow terms
PREN	Pitting resistance equivalent number	PREN table
CRA	Corrosion-resistant alloy	materials
UHP	Ultra-high purity	high-purity selection
EP	Electropolishing	electropolished tubing
MTC	Mill test certificate (EN 10204)	EN 10204 MTC
PMI	Positive material identification	traceability
NDT	Non-destructive testing	testing & inspection
NPT / NPTF	National Pipe Taper / Dryseal NPT	NPT
BSPP / BSPT	British Standard Pipe Parallel / Tapered	BSPP vs BSPT
VCR / VCO	Metal-gasket / O-ring face-seal fittings	face-seal fittings
TAA	Trade Agreements Act (country of origin)	US-origin compliance
UNS	Unified Numbering System (alloy ID)	materials

Why source instrumentation fittings & valves from Crestflo

Crestflo makes instrumentation fittings, valves and tubing for the US market, built for drop-in interchange with Swagelok, Parker, Hoke, Hy-Lok and Fitok patterns. Compression tube fittings carry ASTM F1387 performance qualification. Valves, in turn, qualify to ASME B16.34 and API standards.

Every part carries a heat number, so full traceability comes standard, not as an extra. EN 10204 3.1 material test certificates ship with each order, with 3.2 available on request, and every part goes through PMI verification. Fittings come in imperial and metric sizes, in stainless, high-nickel alloys and titanium. Hardened or non-hardened, the choice is yours.

Crestflo is the instrumentation division of an export house with four decades in business and recognition from the Government of India, plus a solid delivery record across the Middle East. It's a new manufacturing brand. But it's built on real heritage, and that's why the terms in this glossary map directly to parts we actually make.

Swagelok®, Parker®, Hoke®, Hy-Lok® and Fitok® remain trademarks of their respective owners. Crestflo isn't affiliated with any of them, and none of them endorse or sponsor Crestflo. We reference these names for one reason only: to describe dimensional interchangeability.

Ready stock for standard items · made-to-order for specials · 6–8 week delivery.
Indian origin; US / European melt available on request, with full material traceability.
ISO 9001 / 14001 / 45001 & PED certified.
Small MOQ, private-label and custom / made-to-print capability.

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Datasheets & CAD available to customers on request.

Frequently asked questions

What is a ferrule?

Crestflo makes a ferrule, the metal sealing ring that sits inside a compression tube fitting. When you tighten the nut, it swages onto the tube's outside diameter, forming a mechanical seal that's both leak-tight and gas-tight. The company offers single and double ferrules in stainless steel, high-nickel alloys, and titanium, available hardened or non-hardened.

What is another name for a ferrule?

Fluid systems know it by other names too: compression ring, sleeve, or, in some markets, an olive. Don't confuse it with a wire or electrical ferrule, or a golf-club ferrule. This glossary sticks to the fluid-system compression ferrule alone.

What is the difference between a ferrule and a crimp?

A ferrule seals a joint when a threaded nut compresses, or swages, it onto a tube. That joint stays serviceable; you can remake it in a tube fitting whenever needed. A crimp works differently. It's a permanently deformed connection, the kind you'll find in wiring and hose ends, and once it's set, it's set. Don't treat the two as interchangeable.

What does a ferrule look like?

It's a small precision metal ring, or, in a two-piece design, a front and back ferrule, that slips over the tube and sits inside the fitting nut. Once you've made up the joint, it leaves a visible swage mark where it gripped the tube's outside diameter.

What is the difference between a single-ferrule and a double-ferrule fitting?

A single-ferrule fitting relies on one ring that both seals and grips. A double-ferrule fitting splits that job: the front ferrule handles the seal, the back ferrule grips the tube, which holds up better under vibration and pressure cycling. For the full comparison, see single vs double ferrule from Crestflo.

What is a needle valve versus a ball valve?

A needle valve throttles flow precisely, using a tapered stem to fine-tune the rate (it's an instrumentation valve, not a carburetor part). A ball valve works differently: quarter-turn it and you get fast on/off through a bored ball (again, an instrumentation valve, not a plumbing fixture). See needle vs ball valve.

What is NPT?

NPT, short for National Pipe Taper, is a US tapered pipe thread that seals along the thread flanks. ASME B1.20.1 defines it. NPTF, the Dryseal variant, holds tighter tolerances and can seal with less sealant. See ASME B1.20.1.

What is double block and bleed (DBB)?

Double block and bleed puts two isolation points in series, with a bleed valve between them. That lets a line be positively isolated, and confirming it doesn't take much: just vent the cavity. Crestflo's DBB valves are built to ASME B16.34. See double block and bleed valve.

What is a mill test certificate (MTC)?

An MTC is an EN 10204 document that certifies a material's chemistry and mechanical properties. The manufacturer issues a 3.1 on its own. A 3.2 carries a countersignature from an independent inspector too. Crestflo supplies 3.1 as standard and 3.2 on request, and it marks the heat number on every part. See EN 10204 MTC.

What is NACE MR0175 / ISO 15156?

NACE MR0175 / ISO 15156 governs metallic materials for resistance to sulfide stress cracking in sour, H₂S oil-and-gas service. That's the standard Crestflo's fittings and valves are built to meet. Confirm the specific service on your RFQ. See NACE MR0175.

What is PREN?

PREN, the pitting resistance equivalent number, is a calculated index of how well an alloy resists chloride pitting: PREN = Cr + 3.3×Mo + 16×N. The higher the number, the better the resistance. That's the whole reason to step up from 316 to 904L, duplex, or super-duplex. Check Crestflo's PREN comparison table for the full breakdown.

Are Crestflo parts made in the USA?

Crestflo manufactures for the US market and builds its products for drop-in replacement. Standard items ship from ready stock; specials are made to order, typically within a 6-8 week window. Standard product comes from India. US or European melt is available on request, backed by full material traceability, and that's how origin gets documented for TAA purposes. See US-origin compliance.