AIR COMPRESSOR SERVICE: BASIC AIR COMPRESSOR PROBLEMS, AIR COMPRESSOR TROUBLESHOOTING, TROUBLESHOOTING PISTON COMPRESSORS

MOST COMMON ISSUES WITH AIR COMPRESSORS

TROUBLESHOOTING AIR COMPRESSOR PROBLEMS

WWW.HKAIRCOMPRESSORS.COM

214-428-2868

MOTOR ISSUES	Power not on	Turn power on
MOTOR ISSUES	Blown main fuses (size 175% of motor nameplate)	Replace fuses
MOTOR ISSUES	Blown control fuses (size per nec article 450-3)	Replace fuses
MOTOR ISSUES	Breaker tripped	Reset or replace breaker
MOTOR ISSUES	Safety device tripped	Reset safety devices
MOTOR ISSUES	Motor starter overloads tripped	Reset or replace overloads
MOTOR ISSUES	Faulty motor starter coil	Replace starter coil
MOTOR ISSUES	Pressure switch incorrectly set	Adjust pressure switch
MOTOR ISSUES	Pressure switch defective	Replace pressure switch
MOTOR ISSUES	Start switch contacts defective	Replace start switch
MOTOR ISSUES	Auxiliary contacts defective	Replace Auxiliary
MOTOR ISSUES	Loose electrical wire	Tighten electrical wires
MOTOR ISSUES	Wire broken or off terminal	Replace wire or reconnect
MOTOR ISSUES	Thermal overload inside motor tripped	Reset or replace motor
MOTOR ISSUES	Low voltage	Must be 10 % of nameplate
MOTOR ISSUES	Motor defective	Replace motor
MOTOR ISSUES	Wiring incorrect	Correct wiring
STARTER TRIPS	Low voltage (must be within 10% of nameplate	Check voltage @ disconnect
STARTER TRIPS	Wrong heater size (check heater amps)	Replace heaters elements
STARTER TRIPS	Wrong overload setting (check motor amps)	Adjust overload setting
STARTER TRIPS	Loose electrical connection	Tighten all wire connections
STARTER TRIPS	Wire size too small	Install correct size wire
STARTER TRIPS	Motor defective	Replace motor
STARTER TRIPS	Motor sized incorrectly	Resize & replace motor
STARTER TRIPS	Pressure switch unloader defective	Replace pressure switch
STARTER TRIPS	Centrifugal Unloader valve defective	Replace valve
STARTER TRIPS	Electric solenoid unloader valve defective	Replace valve
STARTER TRIPS	Hydraulic unloader valve defective	Replace valve
STARTER TRIPS	In-tank check valve defective	Replace valve
STARTER TRIPS	Unloaders not unloading suction valves	Check for pressure / rebuilt
STARTER TRIPS	Defective compressor valves	Replace compressor valves
STARTER TRIPS	Unloader control line plugged	Replace control line
STARTER TRIPS	Discharge pressure too high	Adjust switch or replace
STARTER TRIPS	Drive belts too tight	Adjust to correct tension
STARTER TRIPS	Head gasket blown between the cylinders	Replace head gasket
STARTER TRIPS	No crankshaft endplay (.001 per inch of bearing od)	Adjust bearings tolerance
STARTER TRIPS	Rod bearing tight or seizing (.001 per inch diameter)	Replace bearings or rods
STARTER TRIPS	Pistons seizing to cylinders	Replace pistons / rebuilt
STARTER TRIPS	Incorrect oil	Change to correct weight
STARTER TRIPS	Intercooler plugging (30-50) psig normal	Remove clean or replace
STARTER TRIPS	Compressor unit seized (locked up)	Remove & disassemble unit
PRESSURE SWITCH	Moisture build up on the switch diaphragm	Replace pressure switch
PRESSURE SWITCH	Ruptured diaphragm (air leak)	Replace pressure switch
PRESSURE SWITCH	Burned contact points	Replace pressure switch
PRESSURE SWITCH	Unloader valve leaking (when running)	Replace pressure switch
PRESSURE SWITCH	Pressure setting changes	Replace pressure switch
PRESSURE SWITCH	Plugged air passage in unloader valve	Replace pressure switch
PILOT VALVE UNLOADER	Pilot valve unloader unloads at to low or high pressure	Adjust pilot unloader valve
PILOT VALVE UNLOADER	Pilot valve unloader loads/unloads excessively	Adjust pilot unloader valve
PILOT VALVE UNLOADER	Pilot valve unloader leaking when running	Replace pilot unloader valve
PILOT VALVE UNLOADER	Pilot valve unloader leaking when stopped	Replace pilot unloader valve
SOLENOID	Solenoid leaking @ exhaust port when stopped	Replace electric solenoid valve
SOLENOID	Solenoid leaking @ cylinder port when running	Replace electric solenoid valve
SOLENOID	Solenoid does not click when electricity is applied	Replace electric solenoid valve
CENTRIFUGAL UNLOADER	Centrifugal Unloader valve leaking when running	Adjust or replace unloader
CENTRIFUGAL UNLOADER	Centrifugal Unloader valve leaking when stopped	Replace in-tank check valve
HYDRAULIC UNLOADER	Hydraulic unloader valve passes air to suction	Adjust oil pressure to 25 psig
HYDRAULIC UNLOADER	unloader when running oil pressure less than 15 psig
HYDRAULIC UNLOADER	Hydraulic unloader valve passes air to suction	Replace hydraulic unloader
HYDRAULIC UNLOADER	unloader when running with 25 psig oil pressure
HYDRAULIC UNLOADER	Hydraulic unloader passes no air to suction unloader when not running	Replace hydraulic unloader
INTERCOOLER SAFETY	Safety Relief valve defective (set 45-100 psig )	Replace Safety relief valve
INTERCOOLER SAFETY	Relief Valve pops off when running & pumping	Replace unloaders or valves
INTERCOOLER SAFETY	Valve pops off when running & not pumping	Replace unloaders or valves
INTERCOOLER SAFETY	Valve pops off when not running	Replace unloaders or valves
INTERCOOLER SAFETY	Intercooler restricted or plugged	Clean or replace intercooler
INTERCOOLER PRESSURE	Defective pressure gauge	Replace air pressure gauge
INTERCOOLER PRESSURE	Leaking intercooler connections	Tighten connection
INTERCOOLER PRESSURE	Leaking intercooler	Replace intercooler
INTERCOOLER PRESSURE	Compressor valves in L.P. defective	Replace valves
INTERCOOLER PRESSURE	Suction Unloaders in L.P. defective	Rebuild or replace
INTERCOOLER PRESSURE	Restricted air inlet filter	Replace inlet filter
INTERCOOLER PRESSURE	Compressor valve defective	Replace compressor valves
INTERCOOLER PRESSURE	Pilot valve defective	Replace pilot valve
INTERCOOLER PRESSURE	Hydraulic valve not functioning properly	Replace hydraulic unloader
INTERCOOLER PRESSURE	Electric solenoid valve not functioning properly	Replace solenoid valve
INTERCOOLER PRESSURE	Worn piston rings	Replace piston rings
DISCHARGE SAFETY	Relief valve defective (set 150% of tank psig)	Replace relief valve
DISCHARGE SAFETY	Restricted in-tank check valve	Replace check valve
DISCHARGE SAFETY	Restricted discharge pipe	Clean or replace pipe
EXCESSIVE AIR	Air pressure gauge inaccurate	Replace air pressure gauge
RECEIVER	Leaks in unloader piping system	Repair leaks in control piping
RECEIVER	Defective compressor suction unloaders	Repair or replace unloader
RECEIVER	Pilot valve set incorrectly or defective	Adjust or replace valve
RECEIVER	Pressure switch set incorrectly or defective	Adjust or replace switch
RECEIVER	Pressure switch wired incorrectly	Correct wiring
RECEIVER	Hydraulic valve not functioning properly	Replace hydraulic valve
RECEIVER	Electric solenoid valve not functioning properly	Replace solenoid valve
RECEIVER	Tube to compressor unloader valve plugged	Replace control air line
BUILDING PRESSURE TOO FAST	Air pressure gauge inaccurate	Replace air pressure gauge
BUILDING PRESSURE TOO FAST	Tank full of water	Drain water from tank
SLOW TANK PRESSURE RAISING	Defective pressure gauge	Replace pressure gauge
SLOW TANK PRESSURE RAISING	Restricted air inlet filter	Replace inlet filter
SLOW TANK PRESSURE RAISING	Pressure switch defective	Replace pressure switch
SLOW TANK PRESSURE RAISING	Pressure switch set wrong	Adjust pressure switch
SLOW TANK PRESSURE RAISING	Unloader pilot defective	Replace pilot valve
SLOW TANK PRESSURE RAISING	Unloader pilot set wrong	Adjust pilot valve
SLOW TANK PRESSURE RAISING	Faulty hydraulic unloader	Replace hydraulic unloader
SLOW TANK PRESSURE RAISING	Electric solenoid valve not functioning properly	Replace solenoid valve
SLOW TANK PRESSURE RAISING	Centrifugal Unloader valve leaking when running	Replace centrifugal valve
SLOW TANK PRESSURE RAISING	Defective compressor valves	Replace compressor valves
SLOW TANK PRESSURE RAISING	Leaking head gasket	Replace head gasket
SLOW TANK PRESSURE RAISING	Loose compressor valves leaking at valve gaskets	Replace valve gasket
SLOW TANK PRESSURE RAISING	Low oil pressure	Adjust oil pressure
SLOW TANK PRESSURE RAISING	Drive belt slipping	Adjust belt tension
SLOW TANK PRESSURE RAISING	Incorrect speed	Change motor pulley
SLOW TANK PRESSURE RAISING	Clogged intercooler (internal)	Clean or replace
SLOW TANK PRESSURE RAISING	Excessive running clearances	Rebuilt compressor pump
SLOW TANK PRESSURE RAISING	Worn piston rings or loose piston	Rebuilt compressor pump
SLOW TANK PRESSURE RAISING	Leaks in the compressed air distribution system	Find & Repair air leaks
SLOW TANK PRESSURE RAISING	Drain valve open	Close drain valve
SLOW TANK PRESSURE RAISING	Pressure relief valve leaking	Replace relief valve
SLOW TANK PRESSURE RAISING	Compressor incorrectly sized for the altitude	Install larger compressor
LOADING AND UNLOADING	Pressure switch defective	Replace pressure switch
LOADING AND UNLOADING	Pilot valve set incorrectly or defective	Replace pilot valve
LOADING AND UNLOADING	Electric solenoid valve not functioning properly	Replace solenoid valve
LOADING AND UNLOADING	Compressor valves defective	Replace compressor valves
LOADING AND UNLOADING	Suction unloaders leaking	Repair leaking unloader
LOADING AND UNLOADING	Compressor operating at incorrect speed	Install correct pulley
LOADING AND UNLOADING	Excessive system leakage	Repair air leaks
LOADING AND UNLOADING	Air receiver tank too small	Install larger receiver tank
LOW OIL PRESSURE	Defective pressure gauge	Replace oil gauge
LOW OIL PRESSURE	Low oil level	Add oil to full mark
LOW OIL PRESSURE	Oil pump direction reversed	Change rotation
LOW OIL PRESSURE	Oil sump strainer plugged	Clean or replace strainer
LOW OIL PRESSURE	Plugged oil filter	Replace oil filter
LOW OIL PRESSURE	Leakage at mains & rod bearings	Rebuilt compressor pump
LOW OIL PRESSURE	Oil pressure adjusting screw not set properly	Adjust oil pressure to spec
USING TOO MUCH OIL	Compressor runs unloaded too long	Run in start/stop position
USING TOO MUCH OIL	Worn piston rings	Replace ring
USING TOO MUCH OIL	Restricted intake system	Replace inlet filter
USING TOO MUCH OIL	Compressor running too hot	See high discharge temp
USING TOO MUCH OIL	Breather valve not functioning properly	Replace breather valve
USING TOO MUCH OIL	Oil level in crankcase too high	Drain to proper oil level
USING TOO MUCH OIL	Oil viscosity wrong for the application	Change to correct viscosity
USING TOO MUCH OIL	Connecting rod out of alignment, bent or twisted	Replace connecting rods
USING TOO MUCH OIL	Leaking oil seal	Replace shaft oil seal
USING TOO MUCH OIL	Piston rings not seated (300 hours for seating)	Change to non detergent oil
USING TOO MUCH OIL	Wrong oil ( detergent oil has a tendency to foam)	Use air compressor oil
HIGH DISCHARGE TEMP.	Defective temperature gauge or switch	Replace temp gauge or switch
HIGH DISCHARGE TEMP.	Compressor valve assemblies defective	Replace compressor valves
HIGH DISCHARGE TEMP.	Pulley/sheave rotation wrong	Change rotation
HIGH DISCHARGE TEMP.	Discharge pressure too high	Adjust pressure lower
HIGH DISCHARGE TEMP.	Ambient temperature too high	Lower ambient temperature
HIGH DISCHARGE TEMP.	Inadequate ventilation or hot air recirculating	Vent hot air out of room
HIGH DISCHARGE TEMP.	Cooling surfaces of compressor excessively dirty	Clean cooling fins
HIGH DISCHARGE TEMP.	Intercooler excessively dirty internal or external	Clean internal & external
HIGH DISCHARGE TEMP.	Defective water temperature regulating valve	Replace water regulating val
HIGH DISCHARGE TEMP.	Clogged water passages in head &/or cylinders	Clean water passages
HIGH DISCHARGE TEMP.	Inadequate cooling water flow	Increase water flow
HIGH DISCHARGE TEMP.	Cooling water temperature too hot	Lower temperature of water
HIGH DISCHARGE TEMP.	Lubrication inadequate	Use air compressor oil
HIGH DISCHARGE TEMP.	Running clearances insufficient	Change clearances
HIGH DISCHARGE TEMP.	Scored or excessively worn cylinder walls	Replace cylinder
KNOCKING	Incorrect speed	Change motor pulley
KNOCKING	Compressor incorrectly size	Install larger compressor
KNOCKING	Loose belts	Adjust belts
KNOCKING	Head clearance insufficient	Check piston to head clearance
KNOCKING	Piston loose in cylinder bore worn piston rings	Rebuilt compressor pump
KNOCKING	Worn rods or main bearing	Rebuilt compressor pump
KNOCKING	Pressure setting excessive high	Adjust to lower pressure
KNOCKING	Crankcase lubrication inadequate	Correct lubrication problem
KNOCKING	Loose pulley/sheave	Tighten pulley & sheave
KNOCKING	Compressor valve assemblies loose	Tighten compressor valves
KNOCKING	Loose compressor or motor mounting bolts	Tighten mounting bolts
KNOCKING	In-tank check defective	Replace check valve
EXCESSIVE BELT WEAR	Pulley/sheave out of alignment	Realign pulley & sheave
EXCESSIVE BELT WEAR	Belt too loose or too tight	Adjust to correct tension
EXCESSIVE BELT WEAR	Belt slipping	Replace belts
EXCESSIVE BELT WEAR	Pulley/sheave wobbling	Tighten to shafts
EXCESSIVE BELT WEAR	Pulley/sheave groove damaged or worn	Replace pulley & sheave
EXCESSIVE BELT WEAR	Incorrect belts	Replace with correct belts
EXCESSIVE VIBRATION	Compressor feet not level	Shim compressor feet
EXCESSIVE VIBRATION	Compressor tightened into a bind	Retighten & shim
EXCESSIVE VIBRATION	Motor or engine not secured tightly	Tighten motor secure
EXCESSIVE VIBRATION	Foundation or frame inadequate	Install correct foundation
EXCESSIVE VIBRATION	Piping inadequately supported	Install additional support
EXCESSIVE VIBRATION	Piping tightened into a bind	Install flexiblemetal hose
EXCESSIVE VIBRATION	Excessive discharge pressure	Lower pressure setting
EXCESSIVE VIBRATION	Loose pulley/sheave	Tighten pulley & sheave
EXCESSIVE VIBRATION	Incorrect speed	Change to correct rpms
EXCESSIVE VIBRATION	Compressor valves not functioning properly	Replace compressor valves
EXCESSIVE VIBRATION	Motor or engine out of balance	Balance motor or engine
RUSTY VALVES/CYCLINDERS	Compressor operated too infrequently	Run compressor more
RUSTY VALVES/CYCLINDERS	Compressor does not run long enough to get hot	Install smaller compressor
RUSTY VALVES/CYCLINDERS	Leaking water jacket or cylinder head	Repair water leak
RUSTY VALVES/CYCLINDERS	Cooling water circulating in compressor too cold	Replace water regulator valve
RUSTY VALVES/CYCLINDERS	System pressure leaking back through compressor	Re-pipe & add a check valve
WATER IN CRANKCASE	Compressor does not run long enough to get hot	Install smaller compressor
MILKY OIL	System pressure leaking back through compressor	Re-pipe & add a check valve
MILKY OIL	Leaking water jacket or cylinder head	Repair water leak
MILKY OIL	Cooling water circulating in compressor too cold	Replace water regulator valve
MILKY OIL	Incorrect or inferior grade of lubricant	Use air compressor oil

AIR COMPRESSOR SERVICE AND REPAIR

WWW.HKAIRCOMPRESSORS.COM

214-428-2868

visit: www.cagi.org

Absolute Pressure - Total pressure measured from zero.

Absolute Temperature - See Temperature, Absolute. https://www.cagi.org/

Absorption - The chemical process by which a hygroscopic desiccant, having a high affinity with water, melts and becomes a liquid by absorbing the condensed moisture.

Actual Capacity - Quantity of gas actually compressed and delivered to the discharge system at rated speed and under rated conditions. Also called Free Air Delivered (FAD).

Adiabatic Compression - See Compression, Adiabatic. https://www.cagi.org/

Adsorption - The process by which a desiccant with a highly porous surface attracts and removes the moisture from compressed air. The desiccant is capable of being regenerated.

Air Receiver - See Receiver. https://www.cagi.org/

Air Bearings - See Gas Bearings. https://www.cagi.org/

Aftercooler - A heat exchanger used for cooling air discharged from a compressor. Resulting condensate may be removed by a moisture separator following the aftercooler.

Ambient Temperature - the temperature of the surrounding environment; technically, the temperature of the air surrounding a power supply or cooling medium; abbreviated [ABM]

Atmospheric Pressure - The measured ambient pressure for a specific location and altitude.

Automatic Sequencer - A device which operates compressors in sequence according to a programmed schedule.

Brake Horsepower (bhp) - See Horsepower, Brake. https://www.cagi.org/

CFM - The amount of air flow delivered under specific conditions, usually expressed in cubic feet per minute (cfm).

Capacity, Actual - The actual volume flow rate of air or gas compressed and delivered from a compressor running at its rated operating conditions of speed, pressures, and temperatures. Actual capacity is generally expressed in actual cubic feet per minute (acfm) at conditions prevailing at the compressor inlet.

Capacity Gauge - A gauge that measures air flow as a percentage of capacity, used in rotary screw compressors

Check Valve - A valve which permits flow in only one direction.

Clearance - The maximum cylinder volume on the working side of the piston minus the displacement volume per stroke. Normally it is expressed as a percentage of the displacement 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 a reciprocating compressor.

Compressibility - A factor expressing the deviation of a gas from the laws of thermodynamics. (See also Super compressibility)

Compression, Adiabatic - Compression in which no heat is transferred to or from the gas during the compression process.

Compression, Isothermal - Compression is which the temperature of the gas remains constant.

Compression, Polytropic - Compression in which the relationship between the pressure and the volume is expressed by the equation pvn is a constant.

Compression Ratio - The ratio of the absolute discharge pressure to the absolute inlet pressure.

Constant Speed Control - A system in which the compressor is run continuously and matches air supply to air demand by varying compressor load.

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. Sometimes it is defined as the highest temperature at which it is possible to liquefy a gas by pressure alone.

Cubic Feet Per Minute (cfm) - Volumetric air flow rate. https://www.cagi.org/

cfm, free Air - cfm of air delivered to a certain point at a certain condition, converted back to ambient conditions.

Actual cfm (acfm) - Flow rate of air at a certain point at a certain condition at that point.

Inlet cfm (icfm) - Cfm flowing through the compressor inlet filter or inlet valve under rated conditions.

Standard cfm (scfm) - Flow of free air measured and converted to a standard set of reference conditions (14.5 psia, 68ºF, and 0% relative humidity).

Cut-In/Cut-Out Pressure - Respectively, the minimum and maximum discharge pressures at which the compressor will switch from unload to load operation (cut in) or from load to unload (cut out).

Cycle - The series of steps that a compressor with unloading performs; 1) fully loaded, 2) modulating (for compressors with modulating control), 3) unloaded, 4) idle.

Cycle Time - Amount of time for a compressor to complete one cycle.

Degree of Intercooling - The difference in air or gas temperature between the outlet of the intercooler and the inlet of the compressor.

Deliquescent - Melting and becoming a liquid by absorbing moisture.

Desiccant - A material having a large proportion of surface pores, capable of attracting and removing water vapor from the air.

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%. The temperature to which air must be cooled, at a given pressure and water-vapor content, for it to reach saturation; the temperature at which dew begins to form.

Demand - Flow of air at specific conditions required at a point or by the overall facility.

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 cooling - 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.

Digital Controls - See Logic Controls. https://www.cagi.org/

Discharge Pressure - Air pressure produced at a particular point in the system under specific conditions.

Discharge Temperature - The temperature at the discharge flange 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.

Droop - The drop in pressure at the outlet of a pressure regulator, when a demand for air occurs.

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)

Efficiency - Any reference to efficiency must be accompanied by a qualifying statement which identifies the efficiency under consideration, as in the following definitions of efficiency:

Efficiency, Compression - Ratio of theoretical power to power actually imparted to the air or gas delivered by the compressor.

Efficiency, Isothermal - Ratio of the theoretical work (as calculated on an isothermal basis) to the actual work transferred to a gas during compression.

Efficiency, Mechanical - Ratio of power imparted to the air or gas to brake horsepower (bhp).

Efficiency, Polytropic - Ratio of the polytropic compression energy transferred to the gas, to the actual energy transferred to the gas.

Efficiency, Volumetric - Ratio of actual capacity to piston displacement.

Exhauster - 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 more nearly isentropically, and thus is more effective in cryogenic systems.

Filters - Devices for separating and removing particulate matter, moisture or entrained lubricant from air.

Flange connection - The means of connecting a compressor inlet or discharge connection to piping by means of bolted rims (flanges).

Fluidics - The general subject of instruments and controls dependent upon low rate of 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 specified location, unaffected by the compressor.

Full-Load - Air compressor operation at full speed with a fully open inlet and discharge delivering maximum air flow.

Gas - One of the three basic phases of matter. While air is a gas, in pneumatics the term gas normally is applied to gases other than air.

Gas bearings - Load carrying machine elements permitting some degree of motion in which the lubricant is air or some other gas.

Gauge Pressure - The pressure determined by most instruments and gauges, usually expressed in psig. Barometric pressure must be considered to obtain true or absolute pressure.

Guide vane - A stationary element that may be adjustable and which directs the flowing medium approaching the inlet of an impeller.

Head, Adiabatic - The energy, in foot pounds, required to compress adiabatically to deliver one pound of a given gas from one pressure level to another.

Head, Polytropic - The energy, in foot pounds, required to compress polytropic to deliver one pound of a given gas from one pressure level to another. https://www.cagi.org/

Horsepower, Brake - Horsepower delivered to the output shaft of a motor or engine, or the horsepower required at the compressor shaft to perform work.

Horsepower, Indicated - The horsepower calculated from compressor indicator diagrams. The term applies only to displacement type compressors.

Horsepower, Theoretical or Ideal - The horsepower required to isothermally compress the air or gas delivered by the compressor at specified conditions.

Humidity, Relative - The relative humidity of a gas (or air) vapor mixture is the ratio of the partial pressure of the vapor to the vapor saturation pressure at the dry bulb temperature of the mixture.

Humidity, Specific - The weight of water vapor in an air vapor mixture per pound of dry air.

Hysteresis - The time lag in responding to a demand for air from a pressure regulator.

Impeller - The part of the rotating element of a dynamic compressor which imparts energy to the flowing medium by means of centrifugal force. It consists of a number of blades which rotate with the shaft.

Indicated Power - Power as calculated from compressor-indicator diagrams.

Indicator card - A pressure - volume diagram for a compressor or engine cylinder, produced by direct measurement by a device called an indicator.

Inducer - A curved inlet section of an impeller.

Inlet Pressure - The actual pressure at the inlet flange of the compressor.

Intercooling - The removal of heat from air or gas between compressor stages.

Intercooling, degree of - The difference in air or gas temperatures between the inlet of the compressor and the outlet of the intercooler.

Intercooling, perfect - When the temperature of the air or gas leaving the intercooler is equal to the temperature of the air or gas entering the inlet of the compressor.

Isentropic compression - See Compression, https://www.cagi.org/

Isothermal compression - See Compression, https://www.cagi.org/

Leak - An unintended loss of compressed air to ambient conditions.

Liquid piston compressor - A compressor in which a vane rotor revolves in an elliptical stator, with the spaces between the rotor and stator sealed by a ring of liquid rotating with the impeller.

Load Factor - Ratio of average compressor load to the maximum rated compressor load over a given period of time.

Load Time - Time period from when a compressor loads until it unloads.

Load/Unload Control - Control method that allows the compressor to run at full-load or at no load while the driver remains at a constant speed.

Modulating Control - System which adapts to varying demand by throttling the compressor inlet proportionally to the demand.

Multi-casing compressor - Two or more compressors, each with a separate casing, driven by a single driver, forming a single unit.

Multi-stage axial compressor - A dynamic compressor having two or more rows of rotating elements operating in series on a single rotor and in a single casing.

Multi-stage centrifugal compressor - A dynamic compressor having two or more impellers operating in series in a single casing.

Multi-stage compressors - Compressors having two or more stages operating in series.

Perfect Intercooling - The condition when the temperature of air leaving the intercooler equals the air at the compressor intake.

Performance curve - Usually a plot of discharge pressure versus inlet capacity and shaft horsepower versus inlet capacity.

Piston Displacement - The volume swept by the piston; for multistage compressors, the piston displacement of the first stage is the overall piston displacement of the entire unit.

Pneumatic Tools - Tools that operate by air pressure.

Polytropic compression -. https://www.cagi.org/

Polytropic head - https://www.cagi.org/

Positive displacement compressors - Compressors in which successive volumes of air or gas are confined within a closed space and the space mechanically reduced, resulting in compression. These may be reciprocating or rotating.

Power, theoretical (polytropic) - The mechanical power required to compress polytropically and to deliver, through the specified range of pressures, the gas delivered by the compressor.

Pressure- Force per unit area, measured in pounds per square inch (psi).

Pressure, Absolute - The total pressure measured from absolute zero (i.e. from an absolute vacuum).

Pressure, Critical – https://www.cagi.org/

Pressure Dew Point - For a given pressure, the temperature at which water will begin to condense out of air.

Pressure, Discharge - The pressure at the discharge connection of a compressor. (In the case of compressor packages, this should be at the discharge connection of the package)

Pressure Drop - Loss of pressure in a compressed air system or component due to friction or restriction.

Pressure, Intake - The absolute total pressure at the inlet connection of a compressor.

Pressure Range - Difference between minimum and maximum pressures for an air compressor. Also called cut in-cut out or load-no load pressure range.

Pressure rise - The difference between discharge pressure and intake pressure.

Pressure, Static - The pressure measured in a flowing stream in such a manner that the velocity of the stream has no effect on the measurement.

Pressure, Total - The pressure that would be produced by stopping a moving stream of liquid or gas. It is the pressure measured by an impact tube.

Pressure, Velocity - The total pressure minus the static pressure in an air or gas stream.

Rated Capacity - Volume rate of air flow at rated pressure at a specific point.

Rated Pressure - The operating pressure at which compressor performance is measured.

Required Capacity - Cubic feet per minute (cfm) of air required at the inlet to the distribution system.

Receiver - A vessel or tank used for storage of gas under pressure. In a large compressed air system there may be primary and secondary receivers.

Reciprocating compressor - Compressor in which the compressing element is a piston having a reciprocating motion in a cylinder.

Relative Humidity - The ratio of the partial pressure of a vapor to the vapor saturation pressure at the dry bulb temperature of a mixture.

Rotor - The rotating element of a compressor. In a dynamic compressor, it is composed of the impeller(s) and shaft, and may include shaft sleeves and a thrust balancing device.

Seals - Devices used to separate and minimize leakage between areas of unequal pressure.

Sequence - The order in which compressors are brought online.

Shaft - The part by which energy is transmitted from the prime mover through the elements mounted on it, to the air or gas being compressed.

Sole plate - A pad, usually metallic and embedded in concrete, on which the compressor and driver are mounted.

Specific gravity - The ratio of the specific weight of air or gas to that of dry air at the same pressure and temperature.

Specific Humidity - The weight of water vapor in an air-vapor mixture per pound of dry air.

Specific Power - A measure of air compressor efficiency, usually in the form of bhp/100 acfm.

Specific Weight - Weight of air or gas per unit volume.

Speed - The speed of a compressor refers to the number of revolutions per minute (rpm) of the compressor drive shaft or rotor shaft.

Stages - A series of steps in the compression of air or a gas.

Standard Air - The Compressed Air & Gas Institute and PNEUROP have adopted the definition used in ISO standards. This is air at 14.5 psia (1 bar); 68 F (20 C) and dry (0% relative humidity).

Start/Stop Control - A system in which air supply is matched to demand by the starting and stopping of the unit.

Super compressibility - See Compressibility. https://www.cagi.org/

Surge - A phenomenon in centrifugal compressors where a reduced flow rate results in a flow reversal and unstable operation.

Surge limit - The capacity in a dynamic compressor below which operation becomes unstable.

Temperature, Absolute - The temperature of air or gas measured from absolute zero. It is the Fahrenheit temperature plus 459.6 and is known as the Rankine temperature. In the metric system, the absolute temperature is the Centigrade temperature plus 273 and is known as the Kelvin temperature.

Temperature, Critical - See Critical Temperature. https://www.cagi.org/

Temperature, Discharge - The total temperature at the discharge connection of the compressor.

Temperature, Inlet - The total temperature at the inlet connection of the compressor.

Temperature Rise Ratio - The ratio of the computed isentropic temperature rise to the measured total temperature rise during compression. For a perfect gas, this is equal to the ratio of the isentropic enthalpy rise to the actual enthalpy rise.

Temperature, Static - The actual temperature of a moving gas stream. It is the temperature indicated by a thermometer moving in the stream and at the same velocity.

Temperature, Total - The temperature which would be measured at the stagnation point if a gas stream were stopped, with adiabatic compression from the flow condition to the stagnation pressure.

Theoretical Power - The power required to compress a gas isothermally through a specified range of pressures.

Torque - A torsional moment or couple. This term typically refers to the driving couple of a machine or motor.

Total Package Input Power - The total electrical power input to a compressor, including drive motor, belt losses, cooling fan motors, VSD or other controls, etc.

Unit type compressors - Compressors of 30 bhp or less, generally combined with all components required for operation.

Unload - (No load) Compressor operation in which no air is delivered due to the intake being closed or modified not to allow inlet air to be trapped.

Vacuum pumps - Compressors which operate with an intake pressure below atmospheric pressure and which discharge to atmospheric pressure or slightly higher.

Valves - Devices with passages for directing flow into alternate paths or to prevent flow.

Volute - A stationary, spiral shaped passage which converts velocity head to pressure in a flowing stream of air or gas.

Water-cooled compressor - Compressors cooled by water circulated through jackets surrounding cylinders or casings and/or heat exchangers between and after stages. https://www.cagi.org/