Plain-language definitions of the terms that appear on valve datasheets, standards and purchase orders — written by the VTXFLOW engineering team.
Double block and bleed is a valve configuration — defined in API 6D — with two seating surfaces that each block flow from line pressure, plus a means …
Read Definition →Double isolation and bleed is an API 6D valve configuration in which at least one seat seals against pressure from both directions, so the body cavity…
Read Definition →A fire-safe valve is designed so that after its soft seals are destroyed by fire, secondary metal-to-metal seating and graphite packing still limit in…
Read Definition →An anti-static device is a set of spring-loaded conductive plungers that maintain electrical continuity between a ball valve's ball, stem and body, so…
Read Definition →A blow-out proof stem is a valve stem assembled from inside the body with an integral shoulder larger than the stem bore, so internal pressure can nev…
Read Definition →Fugitive emissions are unintended leaks of process gas or vapour to atmosphere through valve stem packing, bonnet joints and body seals — individually…
Read Definition →Bubble-tight shutoff means a closed valve shows zero visible bubbles during a low-pressure air or nitrogen seat test with the downstream side monitore…
Read Definition →ANSI/FCI 70-2 defines six seat leakage classes for valves. Class IV (0.01% of rated capacity) is standard metal-seated quality, Class V is a much tigh…
Read Definition →ISO 5208 grades valve seat tightness into rate classes from Rate A (no visually detectable leakage) through AA, B, C, CC, D, E, EE, F and G, each with…
Read Definition →API 598 is the inspection and pressure-testing standard for valves built to API design codes. It requires a shell test at 1.5 times the 38°C rating, a…
Read Definition →A pressure-seal bonnet uses internal line pressure to energise its own sealing: the bonnet sits inside the body neck against a soft iron or graphite g…
Read Definition →A bolted bonnet valve attaches its bonnet to the body with a gasketed, stud-bolted flange joint — the standard construction of API 600 gate valves and…
Read Definition →A welded bonnet valve has its bonnet seal-welded or fully welded to the body, eliminating the gasketed flange joint and its leak path entirely. The co…
Read Definition →An extended bonnet is the elongated neck — typically 250 to 600 mm — between a cryogenic valve's body and its stuffing box. It holds a static column o…
Read Definition →A bellows-sealed valve replaces the sliding stem-packing interface with a welded metal bellows — a flexible, hermetic barrier that stretches and compr…
Read Definition →OS&Y — outside screw and yoke — is a rising-stem valve construction in which the stem threads are outside the pressure envelope, engaging a yoke nut a…
Read Definition →On a rising-stem valve the stem travels up out of the body as the valve opens, showing position directly; on a non-rising stem design the stem only ro…
Read Definition →Valve trim is the set of replaceable internal parts in contact with the process fluid — typically the stem, seat rings, wedge or disc facings and back…
Read Definition →A solid wedge is one rigid piece — strong, simple and standard for general service. A flexible wedge has a peripheral groove letting each face flex in…
Read Definition →A full-bore (full-port) valve has an internal passage matching the pipe's inside diameter, allowing pigging, minimal pressure drop and unrestricted fl…
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