Glossary of Terms

" · in

" (or in) = Inch, an Imperial measurement of distance. 12" = 1'. 1" = 2.54 cm.

' · ft

' (or ft) = Foot, an Imperial measurement of distance. 1' = 12" or 30.48 cm.

1Ph

Sometimes used to represent a single-phase electrical system or equipment. Also written as 1PH.

3Ph

Sometimes used to represent a three-phase electrical system or equipment. Also written as 3PH.

ATA · ata

ata = Atmosphere Absolute, a unit of pressure that measures total pressure relative to a perfect vacuum (absolute zero pressure). 1 ata = 1 atmosphere absolute = 101.325 kPa = 1.01325 bar = 14.7 psi (at sea level). It includes atmospheric pressure (1 atm) + any additional pressure applied. When underwater at a depth where the water pressure adds 2 atmospheres to the 1 atmosphere at the surface: Total pressure = 3 ata (1 atm air + 2 atm water).

ATM · atm

atm = Atmosphere. 1 atm (standard atmosphere) is defined as: 101.325 kPa (kilopascals), 1.01325 bar, 14.7 psi, or 760 mmHg. It represents the average atmospheric pressure at sea level. Atmospheric pressure is also called "gauge pressure," the pressure measured relative to the surrounding atmospheric pressure (not absolute zero pressure).

Airline Respirator

See Supplied-Air Respirator (SAR).

Ambient Air

The natural air in the environment surrounding a machine, typically uncompressed and at room temperature. It consists of ~78% nitrogen, ~21% oxygen, and small amounts of argon, carbon dioxide, water vapor, etc. Most air compressors take in ambient air through a filter at atmospheric pressure and compress it to higher pressures.

Ambient Pressure

The pressure exerted by the atmosphere (or the surrounding environment) at a specific location. At sea level, ambient pressure ≈ 1 atm = 14.7 psi = 1.01 bar. It decreases with altitude and may increase in pressurized environments (like inside a hyperbaric chamber).

Atmospheric Intake Pressure

Refers to the pressure of the ambient air that a compressor or pump takes in directly from the surrounding environment—without any pre-compression. At sea level, atmospheric pressure is approximately: 1 atm, 14.7 psi, 1.01 bar (1013 mbar), or 760 mmHg. This value decreases with altitude (e.g., lower pressure at higher elevations).

Auto Drain · autodrain

Auto Drain (Autodrain) = Automatic Condensate Drain Systems remove liquid produced during the the gas compression cycle (condensate) from the compressor system without manual attention. Drain valves automatically open and close to eliminate accumulated condensate. Auto drains increase filter life and reduces the amount of operator oversight during compressor operation.

BAR · bar

bar = A metric unit of pressure defined as 100,000 Pa (100 kPa). 1 bar = 1.45 psi, or roughly Earth's average atmospheric pressure at sea level. 1 psi = 0.0689 bar. It is not an SI unit of measure.

Booster

Unlike a compressor that takes gas at atmospheric pressure and compressors it, a booster takes an already compressed gas source and further increases the pressure. The booster input range can be ~4–100 bar (58–145 psi). Boosters and used to transfer gases between tanks, laser cutting, scuba/SCBA top-offs, and CNG refueling.

CAD-CAM

CAD-CAM = CAD (Computer-Aided Design) is the use of software to create precise drawings or 3D models of products or parts. CAM (Computer-Aided Manufacturing) takes those digital designs and converts them into instructions for machines (like CNC mills or 3D printers) to produce the physical item.

CFM (cfm)

CFM = Cubic Feet per Minute, a measurement of fluid or gas flow. 1 CFM = 28.316 LPM. Typically written in lowercase "cfm".

CNG

CNG = Compressed Natural Gas.

Compressor

A machine that draws in ambient air or gas, typically at atmospheric pressure (~1 bar or 14.7 psi) and compresses it to a higher pressure for storage or immediate use.

Cyl

Cylinder or Cylinders. A cylinder is the chamber in which a piston moves back and forth to compress air (or gas). It contains the piston, valves, and the space where suction and compression happen. Functionally, the cylinder is the physical component where compression work is performed. One stage can be carried out by one cylinder or multiple cylinders. For example, a two-cylinder, single-stage compressor uses both cylinders to compress air directly from atmospheric pressure to the final pressure. This setup is common in larger low-pressure systems, where using multiple cylinders helps share the load, reduce piston size, and improve cooling.

D · dia

"D" or "dia" = Diameter. It is often shorthand to indicate that the value refers to a circular cross-section or round feature (like a hole, shaft, rod, pipe, or thread). Examples: (a) "10D" = 10 mm diameter rod; (b) "0.250 dia" = 0.250 inch diameter. Note that "Ø20" (without the "D") is also commonly used to represent diameter; in this case, a 20 mm diameter hole.

Duty Cycle

The fraction of one period in which a system is active. Duty cycle is commonly expressed as a percentage. Example: If a compressor runs for 90 minutes ("runtime") and rests for 30 minutes ("rest time") in a 120-minute cycle, its duty cycle is 75%. Equation: 90 minutes ÷ 120 minutes = 75% duty cycle.

G

When use in conjunction with a measurement, like in the phrase [1/4"G], the “G” refers to straight pipe thread, which is formally designated as BSPP (British Standard Pipe Parallel) and also known as “G thread”. G1"F = BSPP non-tapered parallel thread, 1" nominal pipe size, with female (internal thread). G1"M = Male (external) thread equivalent.

GGE

GGE = Gasoline Gallon Equivalent. The GGE (Gasoline Gallon Equivalent) was established to provide a common measure for CNG, allowing consumers and businesses to understand how much CNG is needed to equal the energy content of a gallon of gasoline.

HP

HP = High Pressure, a generalized pressure range of compressors and equipment. At Nardi, high pressure equipment is rated in above 80 bar (580 psi) to 425 bar (6164 psi).

High Pressure

Nardi Compressori refers to "high pressure" as a way to describe equipment that has a maximum working pressure above 80 bar (>1160 psi).

Hookah · Diving Hookah

Hookah = Also known as a Surface Supply System. A device powered by a gas engine or electric motor used to supply air to divers for recreational or limited commercial purposes through the use of a hose connected between the diver's regulator at depth and a low-pressure air pump at the surface. A diving hookah has nothing to do with the consumption of tobacco or any other such products.

Inlet Pressure

The actual pressure (measured in bar or psi) of gas entering a booster. Inlet pressure is a measurable value and is usually specified as a requirement for proper booster operation.

L

L = Liter (or Litre), a metric unit of volume. 1L = 1.05 US liquid quarts. 1 US gallon = 3.785 liters.

L x W x H

L x W x H = Length x Width x Height. Used to describe the size of equipment in a standardized format.

LP

LP = Low Pressure, a generalized pressure range of compressors and equipment. At Nardi, low pressure equipment is rated below 40 bar (<580 psi).

LPM (L/min)

LPM = Liters per Minute, a measurement of fluid or gas flow. 1 LPM = 0.03531 CFM. Also regularly abbreviated as "L/min".

Low Pressure

Nardi Compressori refers to "low pressure" as a way to describe equipment that has a maximum working pressure of below 40 bar (<580 psi).

MP

MP = Medium Pressure, a generalized pressure range of compressors and equipment. At Nardi, medium pressure equipment is rated in the 40 to 80 bar range (580–1160 psi).

Medium Pressure

Nardi Compressori refers to "medium pressure" as a way to describe equipment that has a maximum working pressure of 40–80 bar (580–1160 psi)

Outlet Pressure

Pressure of the air or gas at the point it leaves a compressor or booster. Sometimes referred to a "discharge pressure." The maximum outlet pressure of a compressor or booster is called "Maximum Working Pressure."

Pa

Pa = Pascals, a unit of pressure. 1 Pa = 1 newton per square meter (N/m²). Standard atmosphere = 101,325 Pa. 1 kPa = 1,000 Pa. 1 bar = 100,000 Pa. 1 atm = 101,325 Pa. 1 mmHg ≈ 133.322 Pa. 1 psi ≈ 6,894.76 Pa.

Power

In compressors, power refers to the rate at which work is performed by the motor (electric) or engine (petroleum) to drive the compressor. Power is commonly expressed in [1] Horsepower (hp) – traditional unit used in North America, and [2] Kilowatts (kW) or Watts (W) – international SI units, where 1 hp ≈ 0.746 kW, and 1 kW = 1000 W.

SAR

SAR = Supplied-Air Respirator.

SI

SI = Système International d’Unités, a coherent system of units based on 7 base units from which all other units (called derived units) are defined. Adopted in 1960 by the General Conference on Weights and Measures (CGPM).

Stg

Stage or Stages. In compressor terminology, a stage refers to one complete step of compression where air (or gas) is drawn in, compressed to a higher pressure, and then discharged—usually into the next stage or the final outlet. One stage can be carried out by one cylinder or multiple cylinders. For example, a two-cylinder, single-stage compressor uses both cylinders to compress air directly from atmospheric pressure to the final pressure. This setup is common in larger low-pressure systems, where using multiple cylinders helps share the load, reduce piston size, and improve cooling.

Suction

A general or qualitative term referring to the action of drawing gas in. In low-pressure systems, it can imply a vacuum or near-atmospheric intake, but in boosters, it refers to the intake from a pressurized line. "Suction" is sometimes used interchangeably with "inlet pressure" in describing boosters.

Supplied-Air Respirator

A type of breathing apparatus that delivers clean, breathable air to the user through an airline connected to a stationary compressor. SAR (Supplied-Air Respirators), also called "airline respirators," are commonly used in environments where air may be contaminated or oxygen-deficient, such as painting, coating, abrasive blasting, confined-space entry, and handling hazardous chemicals. Unlike SCBA (Self-Contained Breathing Apparatus), SAR systems do not rely on onboard air cylinders, allowing for longer-duration use without the added weight of tanks.

V

V = Volt, a measure of electromotive force. Usually referenced in power supplies: 12V, 24V, 110V, 230V, 440V, etc.

VAC

VAC = Volts Alternating Current. Usually refers to connection to the energy grid, i.e., 110 VAC, 220 VAC, 440 VAC.

VDC

VDC = Volts Direct Current. Usually refers to connection to a battery, i.e., 12 VDC, 24 VDC.

W

W = Watt, a measure of electrical power. 1000 watts = 1 kW. Usually used to describe the power of an electric motor.

dB

dB = Decibels, a unit to measure the intensity of sound. 60 dB = Normal Conversation. 80 dB = Doorbell. 65–95 dB = Power Lawn Mower. 80–90 dB = Food Processor. Continued exposure to noise above 70 dBA (adjusted decibels) over time will cause hearing loss.

ft/s

ft/s = Feet per Second. In the case of compressors, it is a measurement of airflow inside of ducts. 1 ft/s = 0.3 ft/s.

hp · HP

hp = Horsepower, a unit of measurement of power, or the rate at which work is done, and usually references the output of motors and engines. One imperial horsepower = 745.7 watts (0.7457 kW). Usually written as "10hp" or "10 hp" = 10 horsepower.

kW

kW = Kilowatt, a unit of measurement of power. In the context of compressors, kW can refer to power consumption (electrical power from the grid) or the power of a motor or engine. 1 kW = 1.34 mechanical horsepower (hp).

lbs (lb)

lbs or lb = Pound/s, the Imperial unit of mass equalling 16 ounces or 0.45 kg. 1 kilogram (kg) = 2.2 pounds.

m · mt · mts

"m" or "mt" = Meter/Metre. "mts" = Meters/Metres. An SI base unit for length. 1m ≈ 3 ft 3.37 in.

m/s

m/s = Meters per Second. In the case of compressors, it is a measurement of airflow inside of ducts. 1 m/s = 3.3 ft/s.

mbar

Abbreviation for millibar. 1 mbar = 0.001 bar, 100 pascals (Pa), or 0.0145 psi. Common uses for mbar include: (1) Meteorology · Standard atmospheric pressure ≈ 1013 mbar; (2) Vacuum systems · Low-pressure readings are often given in mbar; and (3) Scientific instruments · Chamber or lab gas pressure. 1 bar = 1000 mbar. 1 atm = 1013.25 mbar. 1 psi ≈ 68.95 mbar.

mmHg

Abbreviation for millimeters of mercury. It is a unit of pressure that originated from measuring how high a column of mercury is pushed by a given pressure. 1 mmHg ≈ 133.322 Pa or ≈ 0.0193 psi. 760 mmHg = 1 atm.

m³/hr

m³/hr = Cubic Meters per Hour, a unit of volumetric flow rate — how much volume of a fluid (liquid or gas) passes through a point or system in one hour. 1 m³/hr = (a) 1,000 L/hr, (b) ~ 16.67 LPM, (c) ~ 0.278 L/sec (LPS), (d) ~ 0.589 CFM, and 9e) ~ 35.31 cubic feet/hour (CFH).

psi

psi = Pounds per Square Inch, a measurement of pressure. 1 psi = 0.0689 bar. 1 bar = 1.45 psi, or roughly Earth's average atmospheric pressure at sea level.

Ø

The symbol "Ø" (phi) is used to (a) symbolize electrical phases, or (b) denote a diameter measurement . (a)"1Ø" = Single-Phase Power. "3Ø" = Three-Phase Power. (b) "Ø10D" = 10 mm diameter. The "Ø" is commonly used for clarity in this context, as in "Ø20" which represents a 20 mm diameter hole.