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Glossary Term: Verification
Activity of demonstrating for each phase of the safety lifecycle by analysis and/or tests that, for the specific inputs, the deliverables meet the objectives and requirements set for the specific phase.
Glossary Term: Venturi meter
A type of flow meter that measures flow rate by determining the pressure drop through a venturi constriction. A venturi is a constriction in a pipe, tube or flume consisting of a tapered inlet, a short straight constricted throat and a gradually tapered outlet; fluid velocity is greater and pressure…
Glossary Term: Vapor pressure
1. The pressure of a vapor corresponding to a given temperature where the liquid and vapor are in equilibrium. Vapor pressure increases with temperature. 2. The pressure (for a given temperature) at which a liquid is in equilibrium with its vapor. As a liquid is heated, its vapor pressure will…
Glossary Term: Valve flow coefficient
(Cv) The number of US gallons (3.785 liters) per minute of 60°F (15.6°C) water that will flow through a valve with a one pound per square inch (6.89 kPa) pressure drop.
Glossary Term: Valve bonnet
An assembly including the part through which a valve plug stem moves and a means for sealing against leakage along the stem. It usually provides a means for mounting the actuator. Sealing against leakage may be accomplished by packing or a bellows. A bonnet assembly may include a packing lubricator…
Glossary Term: Valve body assembly
An assembly of a body, bonnet assembly, bottom flange and trim elements. The trim includes a valve plug which opens, shuts or partially obstructs one or more ports.
Glossary Term: Valve body
The part of the valve which is the main pressure boundary relative to the ambient. The body also provides the pipe connecting ends, the fluid flow passageway, and may support the seating surfaces and the valve closure member.
Glossary Term: Validation
the activity of demonstrating that the safety instrumented function(s) and safety instrumented system〈s〉 under consideration after installation meets in all respects the safety requirements specification.
Glossary Term: V orifice
“V”-shaped flow control orifice which allows a characterized flow control as the gate moves in relation to the fixed Vee opening.
Glossary Term: V Model
The basic project execution model that starts with high level design and goes down to detailed design followed by testing of the detailed design and then testing of the higher level design elements.
Glossary Term: Ultrasonic flow meter
A device for measuring gauge pressure or differential pressure by means of a U shaped transparent tube partly filled with a liquid, commonly water; a small pressure above or below atmospheric is measured by connecting one leg of the U to the pressurized space and observing the height of liquid…
Glossary Term: U tube manometer
A device for measuring gauge pressure or differential pressure by means of a U shaped transparent tube partly filled with a liquid, commonly water; a small pressure above or below atmospheric is measured by connecting one leg of the U to the pressurized space and observing the height of liquid…
Glossary Term: Two-wire transmitter
Electronic transmitter which uses the power wires (typcally 24vdc) for signal transmission, usually by manipulating the current flow (typically 4-20mA) to represent the desired signal.
Glossary Term: Turbine flow meter
A volumetric flow measuring device using the rotation of a turbine type element to determine flow rate.
Glossary Term: Trim
The internal parts of a valve which are in flowing contact with the controlled fluid. Can be designed to any of the following requirements: Anti cavitation: reduces the tendency of the controlled liquid to cavitate. Anti noise: reduces the noise generated by fluid flowing through the valve. Balanced: minimizes the…
Glossary Term: Transient response
The response of a transducer to a step change of input. NOTE: Transient response, as such, is not shown in a specification except as a general heading, but is defined by such characteristics as time constant, response time, ringing period, etc.
Glossary Term: Torque tube flow meter
A device for measuring liquid flow through a pipe in which differential pressure due to the flow operates a bellows, whose motion is transmitted to a recorder arm by means of a flexible torque tube.
Glossary Term: Time constant
1. The value t in an exponential response term. For the output of a first order system forced by a step or an impulse, t is the time required to complete 63.2% of the total rise or decay. In higher order systems, there is a time constant for each of…
Glossary Term: Thermowell
A thermowell is a pressure tight receptacle adapted to receive a temperature sensing element and provided with external threads, flanges or other means for pressure tight attachment to a vessel.
Glossary Term: Thermojunction
Either of the two locations where the conductors of a thermocouple are in electrical contact; one, the measuring junction, is in thermal contact with the body whose temperature is being determined, and the other, the reference junction, is generally held at some known or controlled temperature.
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