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. |
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. |
| De-Air Entrainment |
A
process where entrained air in a liquid system is effectively removed. |
| Degrees Celsius (°C) |
An
absolute temperature scale. ((°F - 32)x 5/9). |
| Degrees Fahrenheit (°F) |
An absolute temperature scale. ((°C x 9/5) + 32). |
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 vapor. |
| Degree Rankin (°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
|
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.
|
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
|
A material having a large proportion of surface pores, capable
of attracting and removing water vapor from the air. |
Design Pressure
|
The
maximum continuous operating pressure as designed by the manufacturer. |
Dew Point
|
The temperature at which moisture in the air will begin to
condense if the air is cooled at constant pressure. At this point the
relative humidity is 100%. |
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. |
Demand
|
Flow of air at specific conditions required at a point or by the
overall facility. |
Desiccant
|
An adsorption
type material used in compressed air dryers. Industry standards are
activated alumina, silica gel and molecular sieves. |
Desorption
|
Opposite of
absorption or adsorption. In filtration, it relates to the downstream
release of particles previously retained by the filter. |
Diaphragm
|
A stationary element between the stages of a multi-stage
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. Also known as diaphragm routing. |
Diaphragm Routing
|
A
method of removing heat from the flowing medium by circulation of a coolant
in passages built into the diaphragm. Also known as diaphragm cooling. |
| Direct Current (DC) |
A continuous, one directional flow of electricity. |
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. |
Digital Controls
|
Control devices, the operation of which may be reduced to
binary operation, such as on off, 0-1, or open closed. Also known as Logic
controls. |
| Diluent |
An inert
substance added so as to reduce the activity of a substance. |
| 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
|
Piping
which is located 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
|
The volume swept out by the piston or rotor(s) per unit of
time, normally expressed in cubic feet per minute. |
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. |
| D.O.E. |
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
|
A pipe
extending downward from the bottom of the air line 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.
|
Droop
|
The drop in pressure at the outlet of a pressure regulator, when a
demand for air occurs. |
Dropleg
|
A pipe coming from the top of the air line 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
|
The
ambient gas temperature as indicated by a standard thermometer. |
Dry Gas
|
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)
|
One
in which there is no liquid injection and/or liquid circulation for
evaporative cooling or sealing. |
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 |
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. |
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
|
Compressors in which air or gas is compressed by
the mechanical action of rotating impellers imparting velocity and pressure
to a continuously flowing medium. (Can be centrifugal or axial design).
|
