Pneumatic Power Variables 311

absolute pressure

psia. The pressure of a gas in a vacuum. Absolute pressure is used in defining standard temperature and pressure.

actual cubic feet per minute

acfm. A measurement of airflow. Actual cubic feet per minute indicates how many cubic feet of air pass by a stationary point in one minute.

actual output

The amount of power a pneumatic power system actually delivers during operation. System operators calculate the efficiency of a compressor by dividing the actual output by the theoretical output.

aftercoolers

A component that cools compressed air coming from a compressor. An aftercooler is a type of heat exchanger that also removes moisture.

air receiver

A pneumatic component that stores compressed gas. A receiver helps stockpile a constant supply of pressurized gas.

ambient air

Gas coming from the surrounding environment. Ambient air is compressed and stored in the air receiver.

area

The size of the space contained within an enclosed two-dimensional figure. Area is typically measured in square units such as square inches or square centimeters.

atmospheric pressure

The weight of the atmosphere. Atmospheric pressure refers to the amount of pressure exerted by the air.

A-weighted decibel scale

A decibel scale that reflects the exclusion of frequencies that humans do not normally hear. A-weighted decibels are abbreviated as dBA.

burst pressure

The pressure rating that indicates the pressure at which a conductor failed during a pressure-rating test. Conductors do not operate near burst pressure in a normally working system.

compressed gas

Any gas held under pressure in a gas cylinder. Compressed gas allows pneumatic systems to perform work.

compressor

A component that pressurizes ambient air in a pneumatic system. The compressor directs pressurized air into the system.

conductor

A component such as a pipe, tube, or hose. Conductors convey fluid throughout a fluid system.

cubic centimeters

cm³. A metric unit of measurement that describes the displacement of a hydraulic component. Cubic centimeters is a measurement of volume.

cubic feet per minute

cfm. A measurement of airflow. Cubic feet per minute indicates how many cubic feet of air pass by a stationary point in one minute.

cubic inches

in³. An English unit of measurement that describes the displacement of a hydraulic component. Cubic inches is a measurement of volume.

cubic meters per hour

m³/hr. A measurement of airflow that indicates how many cubic meters of air pass by a stationary point in one hour.

cubic meters per minute

m³/min. A measurement of airflow that indicates how many cubic meters of air pass by a stationary point in one minute.

cycle

One complete revolution or rotation of a rotary pneumatic component. A cycle may also be one complete extension and retraction of a linear pneumatic component.

decibels

dB. A unit of measurement that describes the intensity of a sound wave. Operators of pneumatic systems measure system noise in decibels.

displacement

A pneumatic power variable that indicates how much air is moved by a pneumatic compressor in one cycle. Displacement is measured in cubic inches per revolution or cubic centimeters per revolution.

effective volume

The flow rate that a pneumatic power system actually delivers during operation. The effective volume is the most important indicator of the capability of the compressor.

efficiency

A measure of the work output of a system versus the total work supplied to it. An efficient system converts a greater percentage of input energy into useful work.

filter

A screen used for limiting contamination by trapping very fine particulate matter and separating this matter from air. A filter is a component of a filter regulator lubricator unit in a pneumatic system.

flow

The directional movement of air in a pneumatic system. Flow in a fluid system can be laminar or turbulent.

flow capacity

A pneumatic power variable that describes how much air is being moved and how much work is being performed. Flow capacity, or flow rate, is usually measured in gallons per minute (gpm) or liters per minute (lpm).

flow rate

A pneumatic power variable that describes how much air is being moved and how much work is being performed. Flow rate is usually measured in cubic feet per minute.

foot-pounds

ft.-lb. A measurement of force indicating the amount of energy needed to move one pound a distance of one foot. Foot-pounds can be used to measure horsepower.

force

The push or pull that gives energy to an object. Force changes the motion or state of rest of an object.

force multiplication

The exponential increase in available power. Pneumatic systems provide high force multiplication.

friction

A force that resists motion between two components that are in contact with each other. Friction can lead to efficiency problems in a pneumatic system.

horsepower

A unit of power used to describe the strength of a pneumatic component. One horsepower equals 33,000 ft.-lb. of work per minute, or 746 watts.

hp

horsepower. A unit of power used to describe the strength of a pneumatic component. One hp equals 33,000 ft.-lb. of work per minute, or 746 watts.

inches per second

ips. In the English system, the number of inches that a pneumatic component travels in one minute. Inches per second is used to measure speed for components such as linear actuators.

intercoolers

A component that cools air inside a compressor. An intercooler is a type of heat exchanger that also removes moisture.

inverse

A fraction obtained by reversing, or inverting, the numerator and denominator. For example, 4/5 is the inverse of 5/4.

laminae

Parallel streams or layers of fluid that flow together and are indicative of laminar flow in a fluid system. Laminae are desirable for proper performance in a fluid system.

laminar flow

A desirable type of fluid flow in which fluid moves smoothly in individual layers or streams called laminae. Laminar flow is also called streamline flow.

linear motion

Motion that takes place along a straight line. Linear motion can be measured using the English or metric system.

maximum allowable working pressure

MAWP. The pressure rating that indicates the greatest pressure a conductor should experience in service. Maximum allowable working pressure is also called working pressure.

millimeters per second

mm/s. A metric unit of measurement. Millimeters per second is the number of millimeters that a pneumatic component such as a linear actuator travels in one second.

newton-meters

Nm. A metric unit of measurement. The newton-meter is used to measure power and torque.

noise

Any unwanted sound. Noise at high decibels is a hearing hazard.

output

A pneumatic power variable that describes how much air is being moved and how much work is being performed. Output, or flow rate, is usually measured in gallons per minute (gpm) or liters per minute (lpm).

pascals

Pa. A metric system unit of pressure. Pascals can be used to measure the amount of pressure in a pneumatic system.

peak values

The point at which horsepower and torque are highest. As speeds increase after the peak values, horsepower and torque decrease.

pistons

A rod inside a cylinder that is moved by hydraulic or pneumatic pressure. Pistons are used at high pressure.

pneumatic power

Power caused by the motion and control of gas, such as air, under pressure. Pneumatic power systems convert energy from pressurized gas into mechanical motion.

pneumatic power variables

A characteristic of a pneumatic system or component that can be measured and quantified. Pneumatic power variables describe the capabilities of each component.

pneumatic system

A system that uses air or other gases to transmit motion to mechanical parts. Pneumatic systems have many power variables that determine their performance.

positive displacement

A type of compressor that moves a fixed amount of air during each cycle. Common types of positive displacement compressors include piston compressors and rotary screw compressors.

pounds per square inch

psi. An English system unit of pressure. Pounds per square inch measures the amount of force that is applied over an area of one square inch.

pressure

The amount of force applied on an object. Pressure is calculated by dividing force by the area.

pressure ratings

An indication of the amount of pressure a fluid conductor can withstand. The pressure rating of a component is provided by the manufacturer.

psi

Pounds per square inch. A unit in the English measuring system used to measure pressure. One psi equals 6.8948 kilopascals.

recovery time

The time it takes for a compressor to replace the pressure in a receiver during operation. Recovery time can be influenced by the speed of the compressor.

revolutions per minute

rpm. A unit of measurement that indicates the number of revolutions a pneumatic component makes in one minute.

rotary motion

Motion that takes place around a point. Rotary motion is circular.

safety ratio

A figure that establishes the relationship between the burst pressure and working pressure. A component with a safety ratio of 4-to-1 will likely fail if the operating pressure reaches a level 4 times the normal level.

speed

The distance an object travels in a given period of time. Speed is used to measure both linear and rotational movement.

standard cubic feet per minute

scfm. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute under standard conditions of temperature, pressure, and humidity.

standard temperature and pressure

STP. An accepted set of conditions for measurement. Standard temperature and pressure is set by industry standards authorities and allows uniform comparisons between sets of data.

streamline flow

A desirable type of fluid flow in which fluid moves smoothly in individual layers or streams called laminae. Streamline flow is also called laminar flow.

swept volume

An indication of the displacement of a pneumatic component that is equal to the volume of the component actually covered by a rotor or piston. Swept volume is constant and does not change.

system delivery pressure

The amount of pressure at the output end of a compressor or receiver in a fluid system. System delivery pressure is used to specify the capability of compressors and is also known as the system working pressure.

system operating pressure

The amount of pressure nearest the point of performing work at the output end of a fluid system. The system operating pressure is used to specify the capabilty of valves and actuators.

system working pressure

The amount of pressure at the output end of a compressor or receiver in a fluid system. System working pressure is used to specify the capability of compressors and is also known as the system delivery pressure.

theoretical output

The amount of power a pneumatic power system is expected to deliver. System operators calculate the efficiency of a compressor by dividing the actual output by the theoretical output.

torque

A force that produces rotary motion. Torque is measured in foot-pounds in the English system and newton-meters in the metric system.

turbulent flow

An undesirable type of fluid flow in which fluid moves in a random and chaotic manner. Turbulent flow works against efficiency in a system.

vacuum

A space with negative air pressure created by the vacuum system. In a vacuum, the pressure inside is lower than the pressure outside.

volume

A measurement of the amount of space contained within a three-dimensional shape. Volume is a pneumatic power variable that describes both the quantity of gas and the capacity of a component.

watts

A unit used to measure power. One horsepower equals 746 watts.

work

The result of a force applied to an object and the distance through which the force is applied. In an equation, work is force multiplied by distance.

working pressure

The pressure rating that indicates the maximum pressure a conductor should experience in service. Working pressure is often called maximum allowable working pressure (MAWP).