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Compressed Air Glossary of Terms :: D ::
Glossary Index
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Dalton's law
-
States that the total pressure of a mixture of gases is equal
to the sum of the partial pressures of the constituent gases. The
partial pressure is the pressure each gas would exert if it alone
occupied the volume of the mixture.
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DC
-
Direct current. A continuous, one directional flow of
electricity
-
Dead end pressure
-
Is the suction pressure attained by an ejector or positive
displacement vacuum pump at zero capacity with the suction
absolutely blanked off.
-
Degrees Celsius (°C)
-
An absolute temperature scale. ((°F - 32)x 5/9).
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Degrees Fahrenheit
(°F)
-
An absolute temperature scale. ((°C x 9/5) + 32).
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Degrees Kelvin (°K)
-
An absolute temperature scale. The kelvin unit of
thermodynamic temperature, is the fraction 1/273,16 of the
thermodynamic temperature of the triple point of water. The triple
point of water is the equilibrium temperature (0,01 °C or
273,16 K) between pure ice, air free water and water vapour.
-
Degree Rankine (°R)
-
An absolute temperature scale. (°F + 459,67).
-
Degree Réaumur
(°Ré)
-
An absolute temperature scale. ((°F - 32) x 4/9).
-
Degree of
intercooling
-
Difference in air or gas temperature between the outlet of the
intercooler and the inlet of the compressor.
-
Degree of saturation
-
Is the ratio of weight of vapor existing in a given space to
the weight that would be present if the space were saturated at
the space temperature.
-
Deliquescent
-
Melting and becoming a liquid by absorbing moisture.
-
Deliquescence
-
A solid absorption agent used in deliquescent type dryers.
-
Delta P
-
Describes the pressure drop through a component and is the
difference in pressure between two points.
-
Delta T
-
A term indicating a temperature relationship between two
temperatures or temperature variation between two points.
-
Demand
-
Flow of air under specific conditions required at a particular
point.
-
Demand side
management (DSM)
-
The planning and implementation of strategies designed to
encourage consumers to improve energy efficiency, reduce energy
costs, change the time of usage, or promote the use of different
energy source.
-
Demulsibility
-
The ability of a fluid that is insoluble in water to separate
from water with which it may be mixed in the form of an emulsion.
-
Density
-
Is the weight of a given volume of gas, usually expressed in
lb / cu ft at SPT condition.
-
Depth filter
-
a filter medium that retains contaminants primarily within
tortuous passages.
-
Desiccant
-
An adsorption type material used in compressed air dryers.
Industry standards are activated alumina, silica gel and molecular
sieves.
-
Design pressure
-
The maximum continuous operating pressure as designed by the
manufacturer.
-
Desorption
-
Opposite of absorption or adsorption. In filtration, it
relates to the downstream release of particles previously retained
by the filter.
-
Dew point
-
Of a gas is the temperature at which the vapor in a space (at
a given pressure) will start to condense (form dew). Dew point of
a gas mixture is the temperature at which the highest boiling
point constituent will start to condense.
-
Dew point cup
-
An apparatus consisting of a small, polished, stainless steel
cup placed in a container into which is passed the sample gas. The
temperature of the polished surface is lowered by immersing dry
ice (solid carbon dioxide) in an acetone solution contained in the
cup. The temperature at which fog appears on the cup is the dew
point of the sample.
-
Diaphragm
-
A stationary element between stages of a multistage
centrifugal compressor. It may include guide vanes for directing
the flowing medium to the impeller of the succeeding stage. in
conjunction with an adjacent diaphragm, it forms the diffuser
surrounding the impeller.
-
Diaphragm compressor
-
Is a positive displacement reciprocating compressor using a
flexible membrane or diaphragm in place of a piston.
-
Diaphragm cooling
-
A method of removing heat from the flowing medium by
circulation of a coolant in passages built into the diaphragm.
-
Differential
pressure
-
The difference in pressure between any two points of a system
or component.
-
Differential
pressure indicator
-
an indicator which signals the difference in pressure between
any two points of a system or a component.
-
Diffuser
-
A stationary passage surrounding an impeller, in which
velocity pressure imparted to the flow medium by the impeller is
converted into static pressure.
-
Direct current
-
DC. A continuous, one directional flow of
electricity.
-
Directional control
valve
-
A valve to control the flow of air in a certain
direction.
-
Dirt holding
capacity
-
The quantity of contaminant a filter element can trap and hold
before the maximum allowable back pressure or delta P level is
reached.
-
Disc
-
The movable seating surface in a valve.
-
Discharge piping
-
Is the piping between the compressor and the aftercooler, the
aftercooler separator and the air receiver.
-
Discharge pressure
-
Is the total gas pressure (static plus velocity) at the
discharge port of the compressor. Velocity pressure is considered
only with dynamic compressors.
-
Discharge
temperature
-
Is the temperature existing at the discharge port of the
compressor.
-
Displacement
compressor
-
A machine where a static pressure rise is obtained by allowing
successive volumes of gas to be aspirated into and exhausted out
of a closed space by means of the displacement of a moving member.
-
Displacement of
a compressor
-
The volume displaced by the compressing element of the first
stage per unit of time.
-
Disposable filter
-
a filter element intended to be discarded and replaced after
one service cycle.
-
DOE
-
The U.S. Department of Energy.
-
DOP
-
Dioctylphalate aerosol (Efficiency Test Material).
-
Double acting
compressor
-
A positive displacement type compressor.
-
Downstream
-
The portion of the flow stream which has already passed
through the system or the portion of the system located after a
filter or separator/filter.
-
Drag
-
Occurs when a valve does not close completely after popping
and remains partly open until the pressure is further reduced.
-
Drain valve
-
A device designed to remove surplus liquid from the compressed
air system. Manual units range from petcock to a ball, gate or
globe valve. Mechanical types consist of ball float. Electrical
drains include solenoid type that is energized by a timer signal,
or electric motor driven units. Also pneumatically activated
drains.
-
Dripleg
-
Is a pipe extending downward from the bottom of the airline to
collect any condensation flow in the pipe.
-
Drive
-
A coupling between the compressor and the engine or motor. The
three types of drives most common are; flange mounted motor, V
belt drive or direct coupling.
-
Dropleg
-
Is a pipe coming from the top of the airline to feed air to an
outlet for tools or air operated devices, so that condensation
does not easily flow into the dropleg.
-
Dry adiabatic lapse
rate
-
Rate at which unsaturated air cools as it travels vertically,
provided that all temperature change is adiabatic (without heat
exchange), and no condensation occurs.
-
Dry bulb temperature
-
Is the ambient gas temperature as indicated by a standard
thermometer.
-
Dry gas
-
Is any gas or gas mixture that contains no water vapor and/or
in which all of the constituents are substantially above their
respective saturated vapor pressures at the existing temperature.
-
Dry unit (oil free)
-
Is one in which there is no liquid injection and/or liquid
circulation for evaporative cooling or sealing.
-
Dynamic losses
-
Friction against duct walls, internal friction in the air mass
and direction variations will cause a speed reduction and are
therefore called dynamic losses.
-
Dynamic type
compressors
-
Machines in which air or gas is compressed by the mechanical
action of rotating vanes or impellers imparting velocity and
pressure to the flowing medium. (Raise the pressure of the air by
converting the energy from the velocity of the air to pressure.)
-
Dynamic viscosity
(
Dynamic
)
-
Is the force in newton required to move a fluid layer of one
square meter area and a thickness of one meter with a velocity of
one meter per second.
-
Dual control
-
Load/unload control system that tries to maximize compressor
efficiency by matching air delivery and air demand. Compressor is
operated at full load or idle.
-
Duct
-
A pipe, tube or channel that conveys a substance (such as air
throughout a building).
-
Durometer
-
This term refers to the hardness or softness of gaskets.
-
Dust cake
-
A layer of dust built up on an air filter.
-
Dust holding
capacity
-
The amount of atmospheric dust which a filter will capture.
-
Duty cycle
-
Percentage of time a compressor unit can operate at full load
over a thirty minute period.
Glossary Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Thanks to Impact RM for permission to reprint the glossary.
Compressed Air Glossary © Impact RM
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