Basic Documentation

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Screwed- end connection — A valve body with a threaded pipe
connection, usually female NPT threads, in valve bodies through 2”.
Seat — The stationary portion of the valve which seals the valve,
thus prevents ow, when in full contact with the movable ball, plug
or disc.
Static Pressure rating — The maximum pressure that the valve
body will tolerate per a dened standard. The standards may dene
the pressure at temperatures other than that observed, so one must
understand the standard to understand the actual pressure rating
for the given application. Common pressure standards for HVAC
valves in North America include ANSI (125, 250) and WOG
(300, 600), but others such as CWP are sometimes used.
Stem — The cylindrical shaft of a control valve moved by an
actuator, to which the throttling plug, ball or wafer disc is attached.
Stroke — The total distance that a linear valve stem travels or
moves. It is also known as lift.
Superheated Steam — Steam at a temperature higher than
saturation temperature at the given pressure.
System Pressure Drop — The sum of all pressure drops in a
Hydronic system.
Three Way Valve — A valve body with one inlet and two outlets or
two inlets and one outlet.
Tight Shut-off — A valve body with no ow or leakage in a closed
position. This is relative to the dened tightness of the seal, usually
dened by a measurement standard. The most common standard
is ANSI/FCI 70 -2, which classies “tightness” from Class I to Class
VI. Class I is non-dened leakage, Class II through Class IV are
descriptive based on leakage as a percent of total capacity, and Class
V and Class VI are descriptive based on leakage as a nite rate per
inch of orice diameter. Since the criteria and testing method for
Class II – IV are signicantly different than Class V – VI, these groups
cannot be directly compared.
Trim — All parts of the valve which are in contact with the owing
media, but are not part of the valve shell or casting. Ball, stem, disc,
plug, and seat are all considered trim components.
Turndown — Ratio between the maximum usable ow and
the minimum controllable ow. Turndown is usually less than
Rangeability, and cannot be applied to a valve exclusive of the
specic application it is placed in, It is a function of the valve,
actuator, piping, coil, and all other system parameters that
determine the maximum usable ow. Since the valve only has
reasonable control over one part of the ratio, the minimum
controllable ow, this is not a good criteria for evaluating
valve quality.
Two-way Valve — A valve body with a single ow path — one inlet
and one outlet.
Valve — A control device which will vary the rate of ow of a
medium such as water or steam.
Valve Actuator — A device that uses a source of power to position
or operate a valve, sometimes also called a valve operator. The
source of power may be anything, examples include manual (via a
hand wheel), pneumatic, or electronic.
Valve Body — The portion of the valve casting through which a
controlled medium ows.
Valve Disc — The movable part of a buttery valve which makes
contact with the seat when the valve is closed.
Valve Flow Characteristic — The relationship between the stem
travel, expressed in percent of travel, and the ow of the uid
through the valve, expressed in percent of full ow or gallons
per minute.
Valve Guide — The part of a globe valve throttling plug that keeps
the disc aligned with the valve seat.
Velocity — The rate of movement for air or water, distance per
unit time.
Viscous — Having a relatively high resistance to ow.
Volumetric Air Flow — Area x Velocity.
Wire Draw — The process where high velocity media erodes a path
across the mechanical components of a valve. This typically occurs
in a stroke valve when the valve is operated primarily with the plug
very close to the seat , causing very high velocities of media across
the plug and seat. The damage appears as if a wire has been drawn
across the components. This differs from the other typical valve
mechanical damage modes – cavitation and ashing – where the
surface appears to have been pulled away as or struck by very small
particles, respectively.
Terminology