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Packing: Rings of flexible material (foil, graphite or synthetic fiber) held in the pump stuffing box by a packing gland or nut. Permits adjustable sealing with minimum maintenance.

Packing-1-: The soft rings that mechanical seal replace to stop leakage. Packing must leak because it works on the theory of a series of pressure drops to reduce the stuffing box pressure to the point where the leakage is acceptable. A minimum of five rings of packing is required to do this.

Pancake-Style Submersible Turbines: have radial flow impellers with multi-vane diffusers enclosed in an outer sleeve.

Parallel circuit: A circuit that contains multiple loads and multiple paths for the flow of current.

Parallel Connection: The arrangement of cells in a battery made by connecting all positive terminals together and all negative terminals together, the voltage of the group being only that of one cell and the current drain through the battery being divided among the several cells.

Parallel operation: The pumps are discharging to a common header. It is important that the impeller speed and outside diameters are the same or one of the pumps will throttle the other.

Partial emission pump: See radial vane pump.

Particle size: The diameter, in millimeters, of suspended sediment or bed material. Particle-size classifications are: [1] Clay: 0.00024-0.004 millimeters (mm); [2] Silt: 0.004-0.062 mm; [3] Sand: 0.062-2.0 mm; and [4] Gravel: 2.0-64.0 mm.

Parts per billion: The number of "parts" by weight of a substance per billion parts of water. Used to measure extremely small concentrations.

Parts Per Million (ppm): The standard measure of total dissolved solids. Parts of dissolved material in one million parts of water. (eg. one pound of mineral salts dissolved in a million pounds of water would be on part per million).

Pascal (pa): A unit of pressure equal to one Newton of force per square meter. One thousand pascals equal one kilopascal (KPa); a kilopascal equals 0.145 pounds per square inch. Alternatively, 1 psi = 6895 Pa = 6.895 kN/sq.m = 0.0703 kg/

Pascal: A metric unit for pressure. 100 kPa = one atmosphere.

Path: The part of a circuit that directs the flow of electricity from the source to the load. Copper wire is used as the path in most circuits.

Pathogen: A disease-producing agent; usually applied to a living organism. Generally, any viruses, bacteria, or fungi that cause disease.

Pathogens: Micro-organism that can cause disease in other organisms or in humans, animals and plants. They may be bacteria, viruses or parasites and are found in sewage, in runoff from animals and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illness.

Peak flow: The maximum instantaneous discharge of a stream or river at a given location. It usually occurs at or near the time of maximum stage.

PEEK (Polyetheretherketone): PEEK is a high-performance engineered thermoplastic which can be used above the useful range of PTFE. PEEK has physical characteristics approaching some metals (approximately 30K tensile) and has excellent resistance to a wide range of organic and inorganic chemicals. PEEK can be used up to 550°F and is an excellent choice for heat transfer fluids, steam and hydrocarbon services.

Per capita use: The average amount of water used per person during a standard time period, generally per day.

Percolation: The movement of water through the openings in rock or soil. (2) the entrance of a portion of the stream flow into the channel materials to contribute to ground water replenishment.

Performance Curve: A chart or graph that illustrates pump performance by plotting the total head and flow rate at various suction lifts. Performance curves for engine-driven pumps also show pump. performance at various engine RPM.  A  curve of flow vs. Total Head for a specific pump model and impeller diameter

Performance curve-1-:  a curve of flow vs. Total Head for a specific pump model and impeller diameter.

Performance curve-2-:  A plot of Total Head vs. flow for a specific pump model, impeller diameter and speed  (same as  characteristic curve, water performance curve).

Performance curves-3-: Chart water flow by comparing total head to flow rate. 

Performance Curves or Pump Curves: a graph-type representation of an operating characteristic of a pump; shows how such a characteristic varies as a function of a single parameter (for example, total head vs. capacity) The "family" or composite graph makes it easier to judge whether a pump model will be useful for the pumping requirements.

Peripheral pump: also known as regenerative or regenerative turbine pump. These are low capacity (150 gpm or 34 m3/h) high head (5400 ft or 1645 m) pumps. The impeller has short vanes at the periphery and these vanes pass through an annular channel. The fluid enters between two impeller vanes and is set into a circular motion, this adds energy to the fluid particles which travel in a spiral like path from the inlet to the outlet. Each set of vanes continuously adds energy to the fluid particles. Peripheral pumps are more efficient at these low flow high head conditions than centrifugal pumps, they also require much less NPSHA than an equivalent centrifugal pump. They can also handle liquids with up to 20% entrained gases. They are used in a wide range of domestic and industrial applications.

Permanent Medium Filter: A filter that utilizes a medium that under normal use will not have to be replaced.

Permanent Split Capacitor (PSC) Motor: A motor that has a run type capacitor in series with the start winding (now referred to as the auxiliary winding) but does not require a switch to disconnect it. The PSC motor is less costly than the cap start motor because a switch is unnecessary and is available from 1/4 to 1-1/2 HP: starting torque is low (30-150% of run torque) and requires the lowest starting current of any design (less than 200% of run current).

Permanently Lubricated Pumps: Without exception, these pumps offer the ideal combination of assets. The oil-filled motor housing design also features a radial lip seal on the motor shaft. They have an exceptional life expectancy, because the oil serves as a continuous lubricant for all the moving parts and the shaft seal. This non-toxic oil, often paired with an aluminum, cast iron, or plastic housing, also helps dissipate heat build-up found in continuous-running pumps. Therefore, the motor stays cool and extends the life of the pump.

Permanently Lubricated: The oil-filled motor housing design also features a radial lip seal on the motor shaft. They have an exceptional life expectancy, because the oil serves as a continuously lubricate for all the moving parts and the shaft seal. This non-toxic oil, often paired with an aluminum, cast iron, or plastic housing, also helps dissipate the heat build-up found in continuous-running pumps. Therefore the motor stays cool and extends the life of the pump.

Permeability: The ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, don't allow water to flow freely.

Permeable: Allowing some material to pass through.

PH: A measure of the acidity or the alkalinity of a fluid. The scale ranges from 0 (acid) to 14 (alkali) with 7 considered neutral.

PH-1-: A measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions. View a diagram about pH.

PH-2-: A measurement of water acidity or alkalinity using a scale of 0 to 14. 7 = neutrality, numbers less than 7 = acidity, numbers greater than 7 = alkalinity. Relative acidity or alkalinity of a substance, such as water, as indicated by the hydrogen ion concentration.

PH-3-: The scale of relative acidity or alkalinity, expressed in logarithmic numbers from 0 - 14, with 7.0 being neutral. What's really being measured is the hydrogen ion concentration.

Phase Angle: The difference between the phase of a sinusoidally varying quantity in a multi-phase motor and the phase of a second quantity which varies sinusoidally at the same frequency. Also known as phase difference.

Phase: Indicates the space relationships of windings and changing values of the recurring cycles of AC voltages and currents. Due to the positioning (or the phase relationship) of the windings, the various voltages and currents will not be similar in all aspects at any given instant. Each winding will lead or lag another in position. Each voltage will lead or lag another voltage in time. Each current will lead or lag another current in time. The most common power supplies are either single- or three-phase (with 120 electrical degrees between the three- phases).

Phenols: Weak aromatic acids, which are indicative of industrial pollution of water supplies. When combined with chlorine, they produce an objectionable taste and odor.

Pinching Hazard: Any configuration of components that would pinch or entrap the fingers or toes of a bather.

Pipe friction loss: The positive head loss due to friction resistance between the pipe walls and the moving liquid.

Pipe Roughness: A measurement of the average height of peaks producing, roughness on the internal surface of pipes. Roughness is measured in many locations, and is usually defined in micro-inches RMS (root mean square).

Pipe strain: The strain on the pump volute caused by the piping. It will cause excessive mechanical seal movement and can cause contact between rotating and stationary pump and seal components.

Piping pressure (maximum): It may be necessary in certain applications to check the maximum rating of your pipes to avoid bursting due to excessive pressure. The ASME pressure piping code B31.3 provides the maximum stress for pipes of various materials. Also the pipe flange rating will have to be checked.

Pitot pump: Also know as rotating casing pump. This pump’s specialty is low to medium flow rates at high pressures. It is frequently used for high pressure shower supply on paper machines.

Pitting: Surface voids caused by corrosion, erosion or cavitation.

Plaster: A common type of interior finish applied over the concrete shell of an in-ground swimming pool.

Plates: Another term meaning much the same as electrodes.

Plumber's Snake: Sometimes known as a "toilet jack," is a flexible auger used to remove clogs in plumbing that cannot be loosened with a plunger. Most devices consist of a coiled metal wire with space between the coils at the end. The other end is attached to a device with a crank that rotates the wire as it moves down into the pipe. Drains are cleared by one of several mechanisms:The auger end of the wire digs itself into the clog much like a corkscrew, allowing retrieval of the object causing the clog when the snake is pulled out. (Commonly hair, combs, small toys, cloth.) The end of the snake breaks up the object, allowing it to pass through the drain. (Commonly tree roots, foam insulation, plastic objects.) The snake flails around the inside surface of the pipe, scraping off accumulated matter (ranging from mineral deposits to bacon fat) which was reducing the effective interior diameter of the drain pipe. The auger should be turned clockwise only, unless it has become jammed in the drain. Not only is this essential for retrieval of foreign objects, but for the longevity of the cable.

Plunger: The sliding disc assembly that changes valve position in a push-pull valve. For example; up for backwash, down for filtration.

Point-source pollution: Water pollution coming from a single point, such as a sewage-outflow pipe.

Polarity: Refers to the charges residing at the terminals of a battery.

Poles: A method of classifying motors by the number of "poles" or pairs of windings.

Poles: In an AC motor, refers to the number of magnetic poles in the stator winding. The number of poles determines the motor's speed. (See "Synchronous Speed") In a DC motor, refers to the number of magnetic poles in the motor. They create the magnetic field in which the armature operates (speed is not determined by the number of poles).

Polyamide: A synthetic polymer of the nylon family used in the fabrication of reverse osmosis and ultrafiltration membranes.

Polychlorinated biphenyls (PCBs): A group of synthetic, toxic industrial chemical compounds once used in making paint and electrical transformers, which are chemically inert and not biodegradable. PCBs were frequently found in industrial wastes, and subsequently found their way into surface and ground waters. As a result of their persistence, they tend to accumulate in the environment. In terms of streams and rivers, PCBs are drawn to sediment, to which they attach and can remain virtually indefinitely. Although virtually banned in 1979 with the passage of the Toxic Substances Control Act, they continue to appear in the flesh of fish and other animals.

Polymer: An algaecide / algaestat made up of repeating polymer molecules. Used for green algae and available in varying strengths.

Polymers: A chemical compound with many repeating structural units.

Polyphase Motor: Two- or three-phase induction motors have their windings, one for each phase, evenly divided by the same number of electrical degrees. Reversal of the two-phase motor is accomplished by reversing the current through either winding. Reversal of a three-phase motor is accomplished by interchanging any two of its connections to the line. Polyphase motors are used where a polyphase (three-phase) power supply is available and is limited primarily to industrial applications. Starting and reversing torque characteristics of polyphase motors are exceptionally good. This is due to the fact that the different windings are identical and, unlike the capacitor motor, the currents are balanced. They have an ideal phase relation, which results in a true rotating field over the full range of operation from locked rotor to full speed.

Polypropylene:  Polypropylene (PP), also known as polypropene, is a thermoplastic polymer material resistant to a wide range of chemicals and is generally suitable for many applications.  An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. It is used extensively in the manufacture of pumps.

Polysulfone: A synthetic polymer used to fabricate reverse osmosis and ultrafiltration membranes, which are characterized by extreme thermal stability and chemical resistance. Popular in dental waterline filtration systems.

Polyvalent Ion: A cation or anion having a multiple electrical charge.

Polyvinyl Chloride (PVC): A thermoplastic piping material produced by the polymerization of vinyl chloride.

Pool Boiler: A type of pool heater operating as an Indirect Type, but using steam instead of hot water in the closed system.

Pool Depth: The vertical distance between the floor level and or which is inclined 45° or less from horizontal. The normal or operating water level when the pool is in use.

Pool Floor: That portion of the pool interior which is horizontal or which is inclined 45° or less from horizontal.

Pool Heater: A device through which pool water is circulated to increase the temperature of the water. In the Direct Type, the heat is transferred directly to the pool water circulating tubes. The Indirect Type utilizes a separate enclosed system which is directly exposed to heat generator and which heats the pool water by circulating the steam or hot water around the tubes of a heat exchanger through which the water circulates. The heat generator is considered part of every heater.

Pool Wall: The sides of a pool above the floor which are vertical at the top and coved at the bottom, or which are inclined to the pool no more than 45° from the vertical.

Pools Above ground/Portable Swimming Pool: A removable pool of any shape that is deeper than forty-two inches (42”) or holds more than 2,500 gallons of water or has a water surface area in excess of 150 square feet. The aboveground pool frame is located entirely above ground and may be readily disassembled for storage and reassembled to its original integrity.

Pools In Ground Swimming Pool: Any pool, spa or hot tub whose sides rest in partial or full contact with the earth.

Pools: Non-Permanently Installed Swimming Pool: One that is so constructed that it may be readily disassembled for storage and reassembled to its original integrity.

Pools On-Ground Swimming Pool: Any pool, spa or hot tub whose sides rest fully above the surrounding earth and that has a deep area below the ground level.

Pools Public Class A: Competition. Any pool intended for use for accredited competitive aquatic events such as FINA, AAU, NCAA, N.F., etc. The pool may also be used for recreation.

Pools: Public Class B: Any pool intended for public recreational use.

Pools: Public Class C: Any pool operated solely for and in conjunction with lodgings such as hotels, motels, apartments, condominiums, etc.

Pools Public Class D: Special Purpose: Any pool operated for medical treatment, water therapy or non-recreational functions.

Pools Public Type VI thru Type X: Public Pools suitable for the installation of diving equipment by type. Diving equipment classified at a higher type may not be used on a pool of lesser type (i.e., Type VIII equipment on a Type VI pool).

Pool: Public: Any pool, other than a residential pool, which is intended to be used for swimming or bathing and is operated by an owner, lessee, operator, licensee or concessionaire, regardless of whether a fee is charged for use.

Pools Residential: A residential pool shall be defined as any constructed pool, permanent or non-portable, that is intended for noncommercial use as a swimming pool by not more than three-owner families and their guests and that is over twenty-four inches (24”) in depth, has a surface area exceeding 250 square feet and/or a volume over 3,250 gallons. Residential Pools shall be further classified into types as an indication of the suitability of a pool for use with diving equipment.

Pools Residential Type I thru Type V Diving Equipment: Residential pools suitable for the installation of diving equipment by type. Diving equipment classified at a higher type may not be used on a pool of lesser type (i.e., Type III equipment on a Type II pool).

Pools Residential Type Q: Any residential pool where the installation of diving equipment is prohibited.

Pools Wading: A pool that may range in water depth from two feet (2’) to zero feet (0’) for wading.

Pore: An opening in a membrane, which allows certain components to pass through, but not others.

Porosity: A measure of the water-bearing capacity of subsurface rock. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer because the pores are usually so small.

Positive displacement pump: Remove water from cylinder by directly applying pressure to a diaphragm or piston or a flexible impeller and cam. Check valves are used to preserve the pressure down line except in the case of the flexible impeller and cam. Usually diaphragm or flexible impeller or piston pumps are used for more exact amounts of water and for higher pressures. This makes them ideal for solar applications, RV's, pressure washers, small cabins, R.O., misters or situations where water demand is low but pressure demand is high. A centrifugal pump is limited in the pressure it can produce unless the design of the pump allows for impeller stacks. This type of pump is usually self priming a few feet.

Positive displacement pumps-1-:  Positive-displacement pumps are used in water supply operations for feeding chemicals at various stages of the treatment process. They displace a certain volume of water in each stroke as they operate. These pumps are not suitable for pumping large volumes of water, they are more suited for high pressure and low flow service. There are two types of positive-displacement pumps: reciprocating pumps and rotary pumps.

Positive Electrode: The electrode of a battery which normally has a shortage of electrons due to the internal chemical reaction.

Positive Terminal: The terminal of a battery toward which electrons flow through the external circuit when the cell discharges.

Potable Water: Any water, such as an approved domestic water supply, which is bacteriologically safe and otherwise suitable for drinking.

Potassium Permanganate: An oxidizing agent commonly used for the regeneration of manganese green sand iron filters and occasionally used as a disinfectant.

Potassium Permonosulfate: See non-chlorine shock.

Potential energy: a thermodynamic property. The energy associated with the mass and height of a body above a reference plane.

Power end: The end of the pump that attaches to the power source and does not get wet from the pumpage. The bearings are in this part.

Power factor: A measure of how the voltage leads or lags the amperage.

Power Factor-1-: Motors typically do not have a rating in watts. Instead you get amps at rated voltage and full load. To relate the voltage and amperage ratings to the horsepower, they must be converted to watts. As stated above, watts is volts times amps. However, this is not true for AC (alternating current) systems as we typically describe them. Typical "AC voltages" are only averages, known as RMS or Root-Mean-Square averages. Thus "120 Volts" really means that the average voltage, when computed by this particular method, is 120. The actual voltage is 170sin(21600t), where t is in seconds and the sin is of degrees. The current is Ipeaksin(21600t + a), where Ipeak is the peak current in amps, t is in seconds, and a is the phase angle in degrees. Clearly we want to avoid multiplying these two and instead figure out how to use the averages. This is done with the power factor, which is the cosine of the phase angle. power (RMS Watts) = Voltage (RMS volts) x Current (RMS amps) x Power-Factor RMS power is what your power meter measures and what converts to horsepower, so that is the figure you want. For resistive loads such as light bulbs and toasters the power factor is 1.0. Thus a light bulb rated at 120 VAC and drawing 1 amp will draw a power of (120 volts)(1 amp)(1.0) or 120 watts. For reactive loads, which include motors, the power factor is always less than 1. Motor power factors typically range from 0.5 to 0.95. For motors from 1 to 10 HP the power factor would typically increase from 0.75 to 0.85 for single phase induction motors. Like efficiency, the power factor is only valid at full load. It drops significantly for a partial load. As an example, consider a motor rated at 15 amps for 120 VAC with an efficiency of 0.75 and a power factor of 0.7. The net power in watts would be (15 A)(120 V)(0.75)(0.7) or 945 watts. At 746 watts per horsepower the proper rating would be about 1 1/4 HP. Smaller motors usually will not have either the efficiency nor the power factor on the nameplate. You can usually get their product and hence if one is given you can get the other. For example, consider a motor rated at 1 1/2 HP, 18 amps at 120VAC with a 63% efficiency. Its power output is (1.5 HP)(746 watts/HP) or 1119 watts. Based on the efficiency alone we would expect to get (18 A)(120 V)(0.63) or 1361 watts. Hence the power factor is (1119 W) / (1361 W) or 0.82. Note that power factors do not affect residential electric bills; you only pay for the wattage. However, if you size a circuit breaker for a low power factor motor based on wattage rather than volt-amps, it might turn out to be too small. And if you are an industrial customer, you can expect to pay more for low power factor machines (since it costs the utility more to transmit the extra current.).

Power Factor-2-: Reactive Power / Apparent Power; electric utilities prefer power factors as close to 100% as possible, and sometimes charge penalties for power factors below 90%.

Power Factor-3-: The power factor of an AC electrical power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit, and is a dimensionless number between 0 and 1. Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power will be greater than the real power.

Power Factor-4-:  A value used to calculate the correct wattage for a circuit with an alternating current.

Power: The rate at which work is expended.

PP (Polypropylene):  Type 1 Polypropylene is a polyolefin, which is lightweight and generally high in chemical resistance. Although Type 1 polypropylene conforming to ASTM D-2146 is slightly lower in physical properties compared to PVC, it is chemically resistant to organic solvents as well as acids and alkalies.  Generally, polypropylene should not be used in contact with strong oxidizing acids, chlorinated hydrocarbons, and aromatics. With a design stress of 1000 psi at 73° F, polypropylene has gained wide acceptance where its resistance to sulfur-bearing compounds is particularly useful in salt water disposal lines, crude oil piping, and low pressure gas gathering systems. Polypropylene has also proved to be an excellent material for laboratory and industrial drainage where mixtures of acids, bases, and solvents are involved. Polypropylene is joined by the thermo-seal fusion process, threading or flanging. At 180°F, or when threaded, PP should be used for drainage only at a pressure not exceeding 20 psi.

PPB: Parts Per Billion (equivalent to micrograms per liter). Unit used for the measurement of the concentration of a chemical or other substance in a liquid.

PPM (Parts Per Million): (equivalent to milligrams per liter). Unit used for the measurement of the concentration of a chemical or other substance in the pool, spa or hot tub water, where this concentration is expressed in terms of “n” molecules of substance per one million molecules of water.

PPM: Parts per million. A method of assigning value to certain concentrations of chemicals in the water. For example, alkalinity should be kept at 80-120 parts per million, by weight and in relation to the water it's dissolved in.

Precharge: The air put into a pressure tank to make it operate within a specific pressure range.

Precharged Tank: A water storage tank pre-charged with air at factory featuring a vinyl bag to separate water from air which prevents waterlogging. This tank design provides greater drawdown than standard tanks. Pre-charged tanks do not require air volume control.

Precipitation: Rain, snow, hail, sleet, dew, and frost.

Precipitation-1-: To precipitate is to come out of solution; become insoluble by result of chemical action. Material forced out of solution, purposefully or accidentally, will then settle, stain or scale, or remain suspended in the water.

Precision bearing: Ball or roller bearing as opposed to a sleeve or babbitt bearing.

Precoat Feeder: A device used to feed a calculated amount of filter aid at the start of a diatomaceous earth filter cycle: following the cleaning operation.

Precoat: The coating of filter aid on the septum of a diatomite type filter at the beginning of each filter cycle.

Pressure Check: Is a test for the rate of water flow; also a test for leaks in plumbing by placing a line in question under pressure and waiting for the pressure to drop.

Pressure Differential: The difference is pressure between two parts of a hydraulic system (influent and effluent of a filter, suction and discharge of a pump, the up and down-stream sides of a venturi or orifice).

Pressure drop: Referring to the loss of pressure from the outside to the inside of the mechanical seal faces or across the individual rings of packing.

Pressure Drop: Sometimes referred to as "delta P", it is the decrease in hydrostatic force (pressure) due to the effects of friction or restrictions on a flowing liquid.

Pressure Gauge: A device indicating pressure in a filter system. Provides a determination of how the system is operating, and informs us when service is required.

Pressure gradient: The pressure drop between the seal faces. Usually illustrated by a wedge.

Pressure head: A measurement of the amount of energy in water due to water pressure.

Pressure head-1-: The pump head exerted by atmospheric pressure or any additional pressure that might be in the vessel.

Pressure head-2-: The vertical distance (in feet) equal to the pressure (in PSI) at a specific point. The pressure head is equal to the pressure in PSI times 2.31 ft.

Pressure head-3-:  An expression of energy, specifically it is energy per unit weight of fluid displaced.  We often need to calculate the pressure head that corresponds to the pressure. Pressure can be converted to pressure head or fluid column height for any fluid. However, not all fluids have the same density. Water for example has a density of 62.34 pounds per cubic foot whereas gasoline has a density of 46.75 pounds per cubic foot. Specific gravity is the ratio of the fluid density to water density at standard conditions. By definition water has a specific gravity (SG) of 1. To convert pressure to pressure head, the specific gravity SG of the fluid must be known.

Pressure head-2-:  The pump head exerted by atmospheric pressure or any additional pressure that might be in the vessel.

Pressure Side: Is the return side of the plumbing. The section from the pump impeller towards the pool.

Pressure Switch: Electrical/pneumatic device used to turn the pump on and off.

Pressure Switch-1-: Is a switch used in pool heaters which opens when the flow rate is insufficient for safe heater operation. This disrupts the circuit in the heater, preventing it from firing.

Pressure: Pressure is force per unit area and is usually listed in psi (pounds per square inch). Pressure is often included in pump performance curves. Pressure and head are directly related when referring to pump performance. The pressure exerted (in psi) at the base of a column of water is 0.433 x Head (in feet). If you attach pressure gauge at the base of a pipe 100 feet tall pipe filled with clear water, you would measure 43.3 psi. Notice how the diameter of the pipe doesn’t affect the pressure value. The maximum pressure (at zero discharge) of any pump can be determined by multiplying the maximum head by 0.433.

Pressure: The application of a force to a body producing more or less compression within the liquid. In a static fluid pressure varies with height. Fluid weight is the cause of hydrostatic pressure. A thin slice of fluid is isolated so that the forces surrounding it can be visualized. If we make the slice very thin, the pressure at the top and bottom of the slice will be the same. The slice is compressed top and bottom by force vectors opposing each other. The fluid in the slice also exerts pressure in the horizontal direction against the pipe walls. These forces are balanced by stress within the pipe wall. The pressure at the bottom of the slice will be equal to the weight of fluid above it divided by the area.

Pressure: The effect produced by the application of force over the surface of an enclosed area.

Pressure-1-:  The application of external or internal forces to a body producing tension or compression within the body. This tension divided by a surface is called pressure.

Pressure-2-:  The force exerted on the walls of a container (tank, pipe, etc.) by the liquid. Measured in pounds per square inch (PSI).

Pressurized Dosing System: A method of delivering effluent to a leaching field in intermittent doses. Requires a 2-1/2 to 4 foot squirt at the end of the system.

Primacy State: A State that has the responsibility and authority to administer EPA's drinking water regulations within its borders. The State must have rules at least as stringent as EPA's.

Primary Battery (Cell): An electrochemical cell or battery which contains a fixed amount of stored energy when manufactured, and cannot be recharged after that energy is withdrawn.

Primary Cell: A cell designed to produce electric current through an electrochemical reaction that is not efficiently reversible. Hence the cell, when discharged, cannot be efficiently recharged by an electric current. Note: When the available energy drops to zero, the cell is usually discarded. Primary cells may be further classified by the types of electrolyte used.

Primary wastewater treatment: The first stage of the wastewater-treatment process where mechanical methods, such as filters and scrapers, are used to remove pollutants. Solid material in sewage also settles out in this process.

Prime: A charge of liquid required beginning the pumping action of centrifugal pumps when the liquid source is lower than the pump.

Prime-1-: A charge of liquid required to begin pumping action of centrifugal pumps when liquid source is lower than pump. May be held in pump by a foot valve on the intake line or a valve or chamber within the pump.

Prime-2-: Most centrifugal pumps require the pump casing to be filled with water before starting.

Prime-3-: The liquid required to begin pumping action.

Prime-4-:  The creation of a partial vacuum inside the pump casing, which allows water to flow into the pump. Prime is the charge of liquid required to begin pumping action when liquid source is lower than pump.  The prime is held in pump by a check valve or foot valve on the intake line or by a valve or chamber within the pump.

Priming: The action of starting the flow in a pump or siphon. With a centrifugal pump, this involves filling the pump casing and suction pipe with water.

Prior appropriation doctrine: The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid West as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to beneficial use has a higher priority of right than a subsequent user. The rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with riparian water rights.

Priority Pollutants: Those pollutants that pose the most serious health hazards determined by the EPA (Environmental Protection Agency).

Private System: An on-site septic system.

Private Water System: An on-site drinking water system made up of a pump, a storage tank and accessories to operate the system automatically. When a faucet is opened in the system, air pressure in the upper part of the tank forces the water to flow out of the tank and into the system. Water pressure falls as the water flows out of the tank. When pressure drops to the cut-in setting of the pressure switch, the switch closes the circuit and the pump starts and runs until system pressure rises to the cut-out setting.

Product Water: The purified water stream from equipment, such as distillation, reverse osmosis and ultra filter units.

Progressive cavity pump: A positive displacement pump. These pumps are ideal for fluids that are just too tough for other pumps to handle. e.g. – pastes, greases, sludge etc. They consist of only one driven metal rotor rotating within an elastomer lined (elastic) stator.  Liquid enters the Suction Inlet under pressure or by gravity and as the ROTOR 1 turns within the flexible rubber STATOR 2 forming tightly sealed cavities 3 which moves the Liquid toward the Discharge Outlet. Pumping action starts the instant the ROTOR turns. Liquid acts as the lubricant between the pumping elements.

Protection (SPP) Device: Senses the power factor as heat builds up in the motor and shuts it down when the preset limit is reached.

Proton: A particle with a positive charge that is located in the nucleus of an atom.

Proton-1-: A stable elementary particle of the baryon family that is a component of all atomic nuclei and carries a positive charge equal to that of the electron's negative charge.

Protozoa: One-celled animals, usually microscopic, that are larger and more complex than bacteria. May cause disease.

Pseudoplastic: The property of a fluid whose viscosity increases slowly with rate of shear.

PSI: A measurement of pressure meaning pounds per square inch.

PSI-1-: An abbreviation for “pounds per square inch” (see “Feet of Head”).

PSI-2-: Pressure expressed in pounds per square inch.

PSIA: Pounds per Square Inch Absolute (above zero PSI).

PSIG: Pounds per Square Inch Gauge (above atmospheric pressure).

PTFE: PTFE stands for PolyTetraFluoroEthylene, (DuPont’s trademark of Teflon) ,PTFE is a thermoplastic member of the fluoropolymer family of plastics. PTFE has a low coefficient of friction, excellent insulating properties, and is chemically inert to most substances. It also can withstand high heat applications and it is well known for its anti-stick properties.

Public Notification: An advisory that EPA requires a water system to distribute to affected consumers when the system has violated MCLs or other regulations. The notice advises consumers what precautions, if any, they should take to protect their health.

Public supply: Water withdrawn by public governments and agencies, such as a county water department, and by private companies that is then delivered to users. Public suppliers provide water for domestic, commercial, thermoelectric power, industrial, and public water users. Most people's household water is delivered by a public water supplier. The systems have at least 15 service connections (such as households, businesses, or schools) or regularly serve at least 25 individuals daily for at least 60 days out of the year.

Public Water System (PWS): Any water system which provides water to at least 25 people for at least 60 days annually. There are more than 170,000 PWS's providing water from wells, rivers and other sources to about 250 million Americans. The others drink water from private wells. There are differing standards for PWS’s of different sizes and types.

Public water use: Water supplied from a public-water supply and used for such purposes as firefighting, street washing, and municipal parks and swimming pools.

Pull Out Torque: Pull Out Torque Same as Breakdown Torque (BDT) or Maximum Run Torque. Usually is the maximum value of torque that a motor will develop without a sudden decrease in speed (breakdown).

Pump And Dump Dosing System: pumps a predetermined amount of effluent to a distribution box where it will gravity feed through the leaching system.

Pump Curves: Performance Curves: a graph-type representation of an operating characteristic of a pump; shows how such a characteristic varies as a function of a single parameter (for example, total head vs. capacity).

Pump Efficiency: The ratio of the water (output) power to the shaft (input) power. Pump efficiency is plotted on performance curves in most cases using what are known as "Iso-Efficiency Curves" When selecting pumps, try to keep the efficiency within 5% of the Best Efficiency Point.

Pump Flange: an external rib, or rim (lip), for strength and for attachment to another object, such as the flange on the end of a pipe or valve. By using flanges, pipes can be assembled or disassembled very easily.

Pump Housing: The pump body or casing. Depending on the design may be made of plastic, aluminum, cast-iron or stainless steel.

Pump out vane: Located behind the impeller shroud in some impeller designs to lower stuffing box pressure. Should no be used in hot well condensate pumps or any pump running with a negative stuffing box pressure.

Pump Strainer Basket: A device placed on the suction side of the pump, which contains a removable strainer basket designed to trap large debris in the water flow without causing restriction. It is sometimes called a Pump Leaf Trap.

Pump Strainer: A device, placed on the suction side of a pump, which contains a removable strainer basket designed to trap debris in the waterflow with a minimum of flow restriction (sometimes referred to in the past as a “Hair and Lint Trap”).

Pump: A mechanical wet-end, powered by an electric motor, which causes hydraulic flow and pressure for the circulation of the pool water.

Pumping Cycles: The times that a pump turns on and off.

Pumping Level: The lowest water level reached during pumping operation.

Pumping level-1-: The vertical distance in feet from the pump to the water level while the pump is operating.If the pump is installed away from the well and is on higher ground, this elevation must also be included. Most wells draw down while being pumped so this must not be confused with the standing water level.

Pumping ring: Used with a convection system to get circulation between two mechanical seals. Absolutely necessary if oil is used as a barrier fluid because of oil's poor specific heat.

Pumping Water Level: the water level in the well when the pump is running and the system is operating as it was designed or as the well driller has tested it.

Puncture Hazard: Any surface or protrusion that would puncture a bather’s skin under casual contact.

Pusher seal: A design that has a spring loaded dynamic elastomer or rubber like part. A very poor design that should be avoided.

Push-Pull Valve: A two position valve used for backwashing sand or DE filters.

PVC (Polyvinyl Chloride): PVC is the most frequently specified of all thermoplastic materials. It has been used successfully for over 30 years in such areas as chemical processing, industrial plating, chilled water distribution, deionized water lines, chemical drainage, and irrigation systems. PVC is characterized by high physical properties and resistance to corrosion and chemical attack by acids, alkalies, salt solutions, and many other chemicals. It is attacked, however, by polar solvents such as ketone, some chlorinated hydrocarbons and aromatics. The maximum service temperature of PVC is 140°F. With a design stress of 2000 psi, PVC has the highest long-term hydrostatic strength at 73°F of any of the major thermoplastics being used for piping systems. PVC is joined by solvent cementing, threading, or flanging.

PVC: Poly vinyl chloride pipe is the most common type of pipe used in areas with warmer climates; it is more rigid than Poly pipe.

PVC-1-: Polyvinyl Chloride Class 12454-B, formerly designated Type 1, Grade 1. PVC is the most frequently specified of all thermoplastic materials. It has been used successfully for over 30 years in such areas as chemical processing, industrial plating, chilled water distribution, deionized water lines, chemical drainage, and irrigation systems. PVC is characterized by high physical properties and resistance to corrosion and chemical attack by acids, alkalies, salt solutions, and many other chemicals. It is attacked, however, by polar solvents such as ketones, some chlorinated hydrocarbons and aromatics. The maximum service temperature of PVC is 140°F. With a design stress of 2000 psi, PVC has the highest long-term hydrostatic strength at 73°F of any of the major thermoplastics being used for piping systems. PVC is joined by solvent cementing, threading, or flanging.

PVC-2-: Polyvinyl chloride, which is used to make flexible and rigid PVC pipe used for pool plumbing.

PVDF (Polyvinylidene Fluoride): KEM-TEMP (KYNAR®) is a strong, tough and abrasion-resistant fluorocarbon material. It resists distortion and retains most of its strength to 280°F. It is chemically resistant to most acids, bases, and organic solvents and is ideally suited for handling wet or dry chlorine, bromine and other halogens. No other solid thermoplastic piping components can approach the combination of strength, chemical resistance and working temperatures of PVDF. PVDF is joined by the thermoseal fusion process, threading or flanging.

Pyrolosis: A breakdown process which occurs when organic matter is subjected to elevated temperatures.