Glossary of Compressed Air Terms :: P :: Glossary Index A B C D E F G H I J K L M N O P Q R S T U V W X Y Z P1 Measuring point for compressor acceptance test. Pressure at the compressor inlet flange. P2 Measuring point for compressor acceptance test. Pressure at the compressor outlet flange. P3 Measuring point for compressor acceptance test. Pressure before an orifice or nozzle, downstream of compressor discharge. P4 Measuring point for compressor acceptance test. Distribution pressure (headers). P5 Measuring point for compressor acceptance test. Pressure at the point of use. Package power The total power absorbed by a compressor, including the power absorbed by all pumps, fans, coolers and the like. Palm coupling A compressed air coupling commonly used on European rail and road vehicles to connect one vehicle to the next. Particle density An important parameter in establishing an entrained particle's potential to impinge on control surfaces and cause erosion. Particulate type filter A device designed to remove solids, such as dirt, scale, rust and other contaminants from the air system. Paving breaker A hand held pneumatic tool. Designed for light demolition work, digging, making holes etc. PDP Pressure dew point temperature (°C). Pedestal type centrifugal compressor A single inlet compressor with the impeller or impellers mounted on a shaft supported by two bearings in a pedestal, with the driver coupled to the compressor shaft. Perfect intercooling Is obtained when the gas is cooled to first stage inlet temperature following each stage of compression. Performance curve A plot of expected operating characteristics (e.g.., discharge pressure versus inlet capacity, shaft horsepower versus inlet capacity). Permeability The relationship of flow per unit area to differential pressure across a filter medium. pH Measure of alkalinity or acidity in water and water containing fluids. Can be used to determine the corrosion inhibiting characteristic in water based fluids. Typically, pH > 8.0 is required to inhibit corrosion of iron and ferrous alloys in water based fluids. Pinion The smaller of two mating or meshing gears; can be either the driving or the driven gear. Piston displacement Net volume actually displaced by the compressor piston at rated machine speed, generally expressed in cubic feet per minute (usually CFM). For multistage compressors, the piston displacement of the first stage only is commonly stated as that of the entire machine. Pleated filter A filter element whose medium consists of a series of uniform folds and has the geometric form of a cylinder, cone, disc, plate ... Synonymous with "convoluted" and "corrugated". Pneumatic Of, relating to, or using air. Moved by air pressure. Filled with compressed air. Pneumatics Engineering science pertaining to gaseous pressure and flow. Pneumatic tools Tools that operate by air pressure. PNEUROP oxidation test (POT) Is a standardized method to determine the carbon formation characteristics of compressor lubricants. Point of use A single outlet or limited number of outlets in a building used to connect tools or equipment to the air system. Pore A small channel or opening in a filter medium which allows passage of gas. Positive displacement compressors Compressors in which successive volumes of air or gas are confined within a closed space, and compressed. They may be either reciprocating or rotating. (Trap air and then squeeze it to the desired pressure). Potential energy is the energy a substance possesses because of its elevation above the earth (or above some other chosen datum plane). . Pounds per square inch PSI - Pounds per square inch. Pour point Is the temperature at which oil begins to flow under prescribed conditions. Power theoretical The mechanical power required to compress polytropically and to deliver, through the specified range of pressures, the gas delivered by the compressor. Power wheel A built in mechanical device to recover a portion of the power consumed by a constant speed centrifugal compressor when operating at reduced capacity or reduced pressure rise, or both. PPB A measurement. Parts per billion PPM A measurement. Parts per million Precool Pre-Cooling of intake air for compressors and Blowers. Precooler Is a heat exchanger located immediately preceding an ejector to condense and remove a portion of the vapor in the mixture and thus reduce the total lb/hr to be handled. Pre open warn An audible or visual discharge at a pressure slightly lower than the set pressure on a valve. Warns the operator that the valve is about to open. Pressure Force per unit area, usually expressed in pounds per square inch (PSI) or BAR. Pressure absolute The total pressure measured from absolute zero ( i.e., from an absolute vacuum). Pressure back The pressure encountered on the return side of a system. Pressure cracking The pressure at which a pressure operated valve begins to pass a gas. Pressure critical Is the saturation pressure at the critical temperature. Pressure dew point Is the temperature at which moisture begins to condense in a compressed air system. Pressure discharge Is the total gas pressure (static plus velocity) at the discharge port of the compressor. Velocity pressure is considered only with dynamic compressors. Pressure drop Resistance to flow. Defined as the difference in pressure upstream and downstream. Pressure gauge A device that indicates pressure differential above or below atmospheric pressure. Pressure inlet Is the total pressure (static plus velocity) at the inlet flange of the compressor. Pressure pot In spray painting applications, a sealed paint cup with a paint gun which puts a measured amount of air pressure into it. This then forces the paint to the gun for atomization. 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 rated The qualified operating pressure which is recommended for a component or a system by the manufacturer. Pressure regulating valve A valve which enables pressure to be reduced, or kept constant at a desired level. Pressure relief device A device actuated by inlet static pressure and designed to open during an emergency or abnormal condition to prevent a rise of internal pressure in excess of a specified value. Pressure rise The difference between the discharge pressure and the intake pressure. Pressure static The pressure measured in a flowing stream (liquid or gas) in such a manner that no effect on the measurement is produced by the velocity of the stream. Pressure system The pressure which overcomes the total resistances in a system. It includes all losses as well as useful work. Pressure total The pressure that would be produced by stopping a moving stream of liquid or gas. Pressure velocity The total pressure minus the static pressure in an air or gas stream. Preventive maintenance Also known as PM, maintenance performed according to a fixed schedule involving the routine repair and replacement of machine parts and components. Process Occurs whenever the system undergoes either a change in state or an energy transfer at a steady stare. Pseudo critical pressure Is the saturation pressure at the critical temperature. It is the highest vapor pressure that the liquid can exert. PSI Pounds per square inch. PSIA Pounds per square inch, absolute. PSID Pounds per square inch, differential. PSIG Pounds per square inch, gauge. Pressure indicated by a pressure gauge. Psychrometry Has to do with the properties of air-water vapor mixtures in the atmosphere. PTFE Polytetrafluorethylene. Pulsation damper A small receiver fitted on the inlet or discharge of a reciprocating compressor. The device is designed to remove the resonance from the compressor thereby reducing noise. Pumping Is the reversal of flow within a dynamic compressor that takes place when the capacity being handled is reduced to a point where insufficient pressure is being generated to maintain flow. Also known as surge. Purge air The portion of dry, full line pressure, compressed air taken from the drying side tower of a dual tower desiccant dryer system. Expanded to a very low pressure and passed across the wet desiccant to strip the moisture in the desiccant of the regenerating tower. In the case of an external blower type dryer, the purge air is atmospheric air compressed by a blower and heated by an external heater to strip moisture off a wet desiccant bed. Glossary Index A B C D E F G H I J K L M N O P Q R S T U V W X Y Z