3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply:
3.1
ANSI rating class
numerical pressure design class defined in ASME B16.5 and used for reference purposes
NOTE The ANSI rating class is designated by the word "Class" followed by a number.
3.2
bi-directional valve
valve designed for blocking the fluid in both downstream and upstream directions
3.3
bleed
drain or vent
3.4
block valve
gate, plug or ball valve that blocks flow into the downstream conduit when in the closed position
NOTE Valves are either single- or double-seated, bi-directional or uni-directional.
3.5
breakaway thrust
breakaway torque
thrust or torque required for opening a valve with maximum pressure differential
3.6
by agreement
agreed between manufacturer and purchaser
3.7
double-block-and-bleed (DBB) valve
valve with two seating surfaces which, in the closed position, blocks flow from both valve ends when the cavity
between the seating surfaces is vented through a bleed connection provided on the body cavity
3.8
drive train
all parts of a valve drive between the operator and the obturator, including the obturator but excluding the operator

3.9
flow coefficient
Kv
volumetric flow rate, in cubic metres per hour, of water at a temperature between 5°C (40°F) and 40°C (104°F) passing through a valve and resulting in a pressure loss of 1 bar (14,7 psi)

NOTE Kv relates to the flow coefficient Cv in US gallons per minute at 15,6°C (60°F) resulting in a 1 psi pressure drop as follows

3.10
full-opening valve
valve with an unobstructed opening capable of allowing a sphere or other internal device for the same nominal size
as the valve to pass
3.11
handwheel
wheel consisting of a rim connected to a hub, for example, by spokes, and used to operate manually a valve
requiring multiple turns
3.12
locking device
part or an arrangement of parts for securing a valve in the open and/or closed position
3.13
manual actuator
manual operator
wrench (lever) or handwheel with or without a gearbox
3.14
maximum pressure differential (MPD)
maximum difference between the upstream and downstream pressure across the obturator at which the obturator
may be operated
3.15
nominal pipe size (NPS)
numerical inches designation of size which is common to components in piping systems of any one size
NOTE The nominal pipe size is designated by the letters NPS followed by a number.
3.16
nominal pressure (PN) class
numerical pressure design class as defined in ISO 7005-1 and used for reference purposes
NOTE The nominal pressure (PN) class is designated by the abbreviation PN followed by a number.
3.17
nominal size (DN)
numerical metric designation of size which is common to components in piping systems of any one size
NOTE Nominal size is designated by the letters DN followed by a number.
3.18
obturator
closure member
part of a valve, such as a ball, clapper, disc, gate or plug, which is positioned in the flow stream to permit or block
flow
3.19
operator
device (or assembly) for opening or closing a valve

3.20
position indicator
device to show the position of the valve obturator
3.21
powered actuator
powered operator
electric, hydraulic or pneumatic device bolted or otherwise attached to the valve for powered opening and closing of
the valve
3.22
pressure class
numerical pressure design class expressed in accordance with either the nominal pressure (PN) class or the ANSI
rating class
NOTE In this International Standard, the pressure class is stated by the PN class followed by the ANSI rating class between
brackets.
3.23
pressure-containing parts
parts, such as bodies, bonnets, glands, stems, gaskets and bolting, designed to contain the pipeline fluid
3.24
pressure-controlling parts
parts, such as seat and obturator, intended to block or permit the flow of fluids
3.25
process-wetted parts
parts exposed directly to the pipeline fluid
3.26
reduced-opening valve
valve with the opening through the obturator smaller than at the end connection(s)
3.27
seating surfaces
contact surfaces of the obturator and seat which ensure valve sealing
3.28
stem
part that connects the obturator to the operator and which may consist of one or more components
3.29
stem extension assembly
assembly consisting of the stem extension and the stem extension housing
3.30
support ribs or legs
metal structure which provides a stable footing when the valve is set on a fixed base
3.31
through-conduit valve
valve with an unobstructed and continuous cylindrical opening
3.32
twin-seat, both seats bi-directional, valve
valve with two seats, each sealing in both directions

3.33
twin-seat, one seat uni-directional and one seat bi-directional, valve
valve with two seats, one sealing in one direction and the other in either direction
3.34
uni-directional valve
valve designed for blocking the flow in one direction only
3.35
venturi plug valve
valve with a substantially reduced opening through the plug and a smooth transition from each full-opening end to
the reduced opening
 

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