TECHNICAL TERMS
After cooler - Heat
exchangers for cooling air or gas discharged from compressors. They provide
the most effective means of removing moisture from compressed air and gases.
Air-Cooled Compressors - Air-cooled
compressors are machines cooled by atmospheric air circulated around the
cylinders or casings.
Base Plate - A metallic structure on
which a compressor or other machine is mounted.
Capacity - The
capacity of a compressor is the full rated volume of flow of gas compressed and
delivered at conditions of total temperature, total pressure, and
composition, prevailing at the compressor inlet. It sometimes means actual flow
rate, rather than rated volume of flow.
Capacity, Actual - Quantity
of gas actually compressed and delivered to the discharge system at rated
speed of the machine and under rated pressure conditions. Actual capacity is
usually expressed in cubic feet per minute (cfm) at that stage inlet gas
conditions.
Casing - The
pressure containing stationary element that encloses the rotor and associated
internal components of a compressor. Includes integral inlet and discharge
corrections (nozzles).
Check valve - A check valve is a valve
that permits flow in one direction only.
Clearance - The
maximum cylinder volume on a working side of the piston minus the piston displacement
volume per stroke. It is usually expressed as a percentage of the displaced
volume.
Clearance Pocket - An
auxiliary volume that may be opened to the clearance space to increase the
clearance, usually temporarily, to reduce the volumetric efficiency of the air
compressor.
Compressibility - A factor
expressing the deviation of a gas from the laws of hydraulics.
Compression, Adiabatic - This type
of compression is effected when no heat is transferred to or from the
gas during the compression process.
Compression, Isothermal - Isothermal
compression is a compression in which the temperature of the gas remains
constant. For perfect gases, it is represented by the equation PV is a
constant, if the process is reversible.
Compression, Polytropic - Compression
in which the relationship between the pre-sum and the volume is
expressed by the equation PV is a constant.
Compression Ratio - The ratio
of the absolute discharge; press = to the absolute inlet pressure.
Critical Pressure - The
limiting value of saturation pressure as the saturation temperature approaches
the critical temperature.
Critical Temperature - The
highest temperature at which well defined liquid and vapor states exist.
It is sometimes defined as the highest temperature at which it is possible to
liquify a gas by pressure alone.
Diaphragm - A
stationary element between the 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 Routing - A method
of removing heat from the flowing medium by circulation of a coolant in
passages built into the diaphragm.
Diffuser - A
stationary passage surrounding an impeller, in which velocity pressure imparted
to the flowing medium by the impeller is converted into static pressure.
Displacement - Displacement
of a compressor is the piston volume swept out per unit time; it is usually
expressed in cubic feet per minute.
Dynamic Type Compressors - Machines
in which air or gas is compressed by the mechanical action of routing
vanes or impellers imparting velocity and pressure to the flowing medium.
Efficiency - Any
reference to efficiency of a dynamic type compressor must be accompanied by a
qualifying statement which identifies the efficiency under consideration, as in
the following
definitions.
Efficiency, Compression - Ratio of
calculated isentropic work requirement to actual thermodynamic work
requirement within the cylinder, the Inner as determined from the cylinder
indicator card.
Efficiency, Isothermal - Ratio of
the work calculated on an isothermal basis to the actual work transferred
to the gas during compression.
Efficiency, Mechanical - Ratio of
thermodynamic work requirement in the cylinder (a shown by die indicator
card) to actual brake horsepower requirement.
Efficiency, Polytropic - Ratio of
the polytropic compression energy transferred to the gas no the actual
energy transferred to the gas.
Efficiency, Volumetric - Ratio of
actual capacity to piston displacement, stated as a percentage.
Exhauster - This is a
term sometimes applied to a compressor in which the inlet pressure is less than
atmospheric pressure.
Expanders - Turbines
or engines in which a gas expands, doing work, and undergoing a drop in temperature.
Use of the term usually implies that the drop in temperature is the principle
objective. The orifice in a refrigeration system also performs this function,
but the expander performs it nearly isentropically, and is thus more effective
in cryogenic systems.
Filters - Filters
are devices for separating and removing dust and dirt front air before it
enters a compress.
Flange Connection - The
flange connection (inlet or discharge) is a means of connecting the casing
to the inlet or discharge piping by means of bolted rims (flanges).
Fluidics - The
general subject of instruments and controls dependent upon low rate flow of air
or gas at low pressure as the operating medium. These usually have no
moving parts.
Free Air - Air at
atmospheric conditions at any specific location. Because the altitude, barometer,
and temperature may vary at different localities and at different times, it
follows that this term does not mean air under identical or standard
conditions.
Gas - While
from a physical point of view a gas is one of the three basic phases of matter,
and thus air is a gas, a special meaning is assigned in pneumatics
practice. The term gas refers to any gas other than air.
GasBearings - Gas
bearings are load carrying machine elements permitting some degree of motion
in which the lubricant is air or some other gas.
Volumetric Efficiency of the
Compressor - It is the ratio of actual volume of air drawn in
the compressor to the stroke volume of the compressor.
Mechanical efficiency - It is the
ratio of indicated power to shaft power or brake power of motor.
Isentropic efficiency - It is the
ratio of the isentropic power to the brake power required to drive the
compressor.
Centrifugal compressor - The flow
of air is perpendicular to the axis of compressor
Axial flow compressor - The flow
of air is parallel to the axis of compressor
Compression - The
process of increasing the pressure of air, gas and vapour by reducing its volume
is called as compression.
Single acting compressor - The
suction , compression and the delivery of air takes on the one side of
piston
Double acting compressor - The
suction, compresstion end the delivery of air takes place on both sides
of the piston.
Multi stage compressor - The
compression of air from initial pressure to the final pressure is carried
out in more than one cylinder.
Application of compressed air -
Pneumatic brakes, drills,jacks,lifts, spray of paintings, shop cleaning
, injecting the fuel in diesel engine, supercharging, refrigeration and in air
conditioning systems.
Inter cooler - It is a simple heat
exchanger, exchanges the heat of compressed air from low pressure
compressor to circulating water before the air enters to high pressure
compressor. The purpose of intercooling is to minimize the work of compression.
Isentropic efficiency - It is
the ratio of isentropic power to the brake power required to drive the compressor.
Clearance ratio - It is the
ratio of clearance volume to the swept volume or stroke volume is called
as clearance ratio.
Isothermal efficiency - It is
the ratio between isothermal work to the actual work of the compressor.
Compression ratio - The ratio
between total volume and the clearance volume of the cylinder is called
compression ratio.
Perfect intercooling - When
the temperature of the air leaving the intercooler is equal to the original
atmospheric air temperature, then the inter cooling is called perfect
intercooling.
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