PARALLEL-BLADE DAMPER: A type of damper where the blades rotate in the same direction.
PARALLEL FANS: Two or more fans that draw air from a common source and exhaust into a common duct or plenum. A parallel fan arrangement is generally used to meet volume requirements beyond that of a single fan. Two identical fans in parallel will effectively deliver twice the rated flow of any one of the fans at the same static pressure.
PARTICLE: A small, discrete mass of solid or liquid material.
PARTICULATE: A particle of solid or liquid matter.
PARTICULATE MATTER: Any solid liquid material in the atmosphere.
PEL (PERMISSIBLE EXPOSURE LIMITS): Limits developed by OSHA to indicate the maximum airborne concentration of a contaminant to which an employee may be exposed.
PERMEABILITY, FABRIC: Measured on Frazier porosity meter or Gurley permeometer. Not to be confused with dust permeability. The ability of air to pass through the fabric, expressed in cubic feet of air per minute per square foot of fabric with 0.5” H2O pressure differential.
PERMIT: An authorization, license or equivalent control document issued by EPA or an approved state agency to implement the requirements of an environmental regulation such as a permit to operate a facility that may generate harmful emissions.
pH: A symbol as part of a logarithmic designation to indicate acidity of alkalinity on a scale from zero to 14. pH7 is taken as neutral, pH6 to zero increasingly acid and pH8 to 14 increasingly alkaline.
PHOTOCHEMICAL PROCESS: The chemical changes brought about by the radiant energy of the sun acting upon various polluting substances. The products are known as photochemical smog.
PHOTOHELIC® GAUGE: Gauge used for measuring pressure drop across filter media and for controlling the on/off function of the cleaning system. The gauge displays static pressure in inches of water and provides adjustable contacts to operate the cleaning system. This is a registered trademark of the Dwyer Company.
PIEZOMETER RING: A device consisting of a number of pressure taps connected to a common manifold to measure pressure.
PILOT VALVE: The small solenoid valve that is electrically operated to relieve pressure on one side of the diaphragm and cause the operation of a larger diaphragm valve.
PITCH DIAMETER: The mean diameter or point at which V-belts ride within a sheave. This dimension is necessary for accurate drive calculations.
PITOT TUBE: A metering device consisting of a double-walled tube with a short rightangle bend. The periphery of the tube has several holes through which static pressure is measured. The bend end of the tube has a hole through which total pressure is measured when pointed upstream in a moving gas stream.
PLEATED FILTER ELEMENT: Filter elements made from any pleated filter media, but primarily applying to those equipped with 100% synthetic fabric.
PLENUM: Pressure equalizing chamber.
PLENUM PULSE: Type of pulsing collector where entire sections of the clean air plenum are isolated and pulsed with either compressed air or air from a high-pressure blower.
PLY: Two or more yarns joined together by twisting.
PM10: A newer standard for measuring the amount of solid or liquid matter suspended in the atmosphere (“particulate matter”). Refers to the amount of particulate matter under 10 micrometers in diameter. The smaller PM10 particles penetrate to the deeper portions of the lungs, affecting sensitive population groups such as children and people with respiratory diseases.
POINT OF OPERATION: The intersection of a fan’s static pressure curve and the system curve to which the fan is being applied. May be designated as velocity pressure divided by static pressure or by a given CFM and SP.
POINT SOURCE: A stationary location or facility from which pollutants are emitted. Also, any single identifiable source of pollution.
POLYMERIZED: A chemical reaction in which two or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules.
POROSITY: Sometimes erroneously used as synonym for permeability. Originally a designation for the amount of air in a fabric such as blankets.
PORTHOLE: The opening in a cartridge dust collector that provides access to the filters.
POUNDS PER 100 POUNDS OF GAS: A common quantitative definition of pollution concentration.
PPM (PARTS PER MILLION): The number of parts of a given pollutant in a million parts of air. Units are expressed by weight or volume.
PRECIPITATORS: Any number of devices using mechanical, electrical or chemical means to collect particulates. Used for measurement, analysis or control. See Electrostatic Precipitator.
PRE-COATING: The application of a relatively coarse, dry dust to a bag or cartridge before start-up to provide an initial filter cake to enhance immediate high efficiency.
PRESEED: Precoating of a dust collector filter (cartridge or bag-type) with material to create a dust cake and ensure peak collection efficiency at system start-up. Usually done when collecting very small particles, such as welding particulate, etc.
PRESSURE, ATMOSPHERIC: The pressure due to the weight of the atmosphere. It is the pressure indicated by a barometer. Standard atmospheric pressure is 29.92 inches of mercury.
PRESSURE DROP: The differential pressure between two points in a system. The resistance to flow between the two points.
PRESSURE, STATIC: The potential pressure exerted in all directions by fluid at rest. For a fluid in motion, it is measured in a direction normally 90° to the direction of flow. Usually expressed in inches water gauge when dealing with air.
PRESSURE, VELOCITY: The kinetic pressure in the directional flow necessary to cause a fluid at rest to flow at a given velocity. Usually expressed in inches water gauge.
PREVENTION OF SIGNIFICANT DETERIORATION (PSD): EPA program in which state and/or federal permits are required that are intended to restrict emissions for new or modified sources in places where air quality is already better than required to meet primary and secondary ambient air quality standards.
PRIMARY COLLECTOR: A dry or wet collector that is followed by a secondary collector with greater filtering efficiency.
PROCESS WEIGHT: The weight per hour that is run through the process. Commonly used in APC codes to determine the maximum allowable pollution exhausted.
PROMULGATE: To make a new law known and put it into effect. The EPA promulgates a rule when it issues the final version in the Federal Register.
PSI (POUNDS PER SQUARE INCH): A measure of pressure .1 psi equals 27.7” water gauge.
PSIA (POUNDS PER SQUARE INCH ABSOLUTE): The absolute pressure without reference to another point. Atmospheric pressure is 14.7 PSIA.
PSIG (POUNDS PER SQUARE INCH GAUGE): The pressure relative to atmosphere. For instance, 10 PSIG equals 24.7 PSIA. This is the more common pressure term.
PSYCHROMETRIC CHART: A graphic depiction of the relationship between pressure, density, humidity, temperature and enthalpy for any gas-vapor mixture. Used extensively in comfort ventilation.
PULSE CYCLE: As used in conjunction with pulse-jet baghouses the interval of time between pulsing a row of bags and that row being pulsed again.
PULSE DURATION: The length of time a pulse lasts. Generally described as the length of time the electrical signal holds the pilot valve open (20-40 milliseconds), however would more correctly be the description of the length of time the manifold is pressurized (120-180 milliseconds).
PULSE INTERVAL: The time between pulsing one row of bags and pulsing the next row.
PULSE JET: Generic name given to all pulsing collectors.
PULSE-JET CLEANING: A cleaning method where a momentary burst of compressed air is introduced through a tube or nozzle to the top cap of a bag. A bubble of air flows down the bag, causing bag walls to collapse behind it. Generic name given to all pulsing collectors.
PULSE PIPE: Pipe used to transport compressed air from the diaphragm valve to the pulse nozzle in reverse pulse cleaning systems. In some manufacturers’ equipment, the pulse pipe delivers the compressed air directly into the filters being cleaned.
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