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Radial bearing: In an end suction centrifugal pump it is the bearing located closest to the stuffing box. This bearing handles most of the radial loads put on the impeller.

Radial Flow Impeller: A pump component in which the liquid enters the eye of the impeller axially and is turned by the impeller vanes and shroud to exit perpendicular to the axis of the pump shaft.

Radial flow pump: Refers to the design of a centrifugal pump for medium head and medium flow or high head and low flow. The value of the specific speed number will provide an indication whether a radial pump design is suitable for your application.

Radial Flow: The flow pattern in which water flows from the outside of a filter element to the center core. For example, a replaceable particulate or carbon cartridge filter unit.

Radial vane pump: Also known as partial emission pump or vane pump. A frame mounted, end suction, top centerline discharge, ANSI pump designed specifically to handle corrosive chemicals at low flows.

Radial: 90 degrees to the centerline of the shaft.

Radiant Extrol Expansion Tank: An Extrol expansion tank specifically designed for high-efficiency radiant systems. The tank is compatible with barrier and non-barrier systems and is useful in glycol applications.

Radionuclides: Any man-made or natural element that emits radiation and that may cause cancer after many years of exposure through drinking water. Can be very long lasting as soil or water pollutants.

Radius: The distance that a sprinkler will throw water. Dependent on pressure and GPM.

Radon: A colorless, odorless naturally occurring radioactive gas formed by the breakdown or decay of radium or uranium in soil or rocks like granite. Radon is fairly soluble in water, so well water may contain radon.

Random Wound: The standard type of stator winding used in motors under 1,000 volts. The coils are random wound with round wire as opposed to flat form wound coils.

Rate Of Flow (GPM): The measurement of the volume of flow per unit of time expressed in gallons per minute.

Rate Of Flow Indicator: A device to indicate the rate of flow in a pipe line (sometimes referred to as a “rate-of-flow meter”).

Rate Of Flow: Quantity of water flowing past a designated point within a specified time period, measured in gallons per minute (gpm).

Rated Capacity: The number of ampere-hours a cell can deliver under specific conditions (rate of discharge, end voltage, temperature); usually the manufacturer's rating.

Rated Full-load Motor Amperage: As the torque load on a motor increases, the amperage required to power the motor also increases. When the full-load torque and horsepower is reached, the corresponding amperage is known as the full-load amperage (FLA). This value is determined by laboratory tests; the value is usually rounded up slightly and recorded as the nameplate value. Rounding up allows for manufacturing variations that can occur and some normal voltage variations that might increase the full-load amps of the motor. The nameplate FLA is used to select the correct wire size, motor starter, and overload protection devices necessary to serve and protect the motor.

Rated Horsepower: The most important power rating of a motor is the "rated horsepower," which is the continuously available net shaft power. This is the power available at the pulley for doing useful work elsewhere. It is typically measured by a dynamometer. These are braking devices attached to the shaft used to measure the net available power. A motor can always produce more than its rated power, but continuously overloading it will reduce its life. Excessive overload will cause it to shut down, or catch fire. An overload will also cause the motor to draw more than its rated current, which risks tripping the circuit breaker.

Rated Pressure: That pressure that is equal to or less than the designed pressure and appears on the data plate of the equipment.

Rated Voltage: Motors are designed to yield optimal performance when operating at a specific voltage level, or a combination of voltage levels in the case of dual-voltage or tri-voltage motors. This value is known as the nameplate voltage. In recognition of the fact that voltage changes on your power distribution system occur due to changing load conditions within your facility and on the utility supply that feeds your facility, motors are designed with a 10% tolerance for voltage above and below the rated nameplate value. Thus, a motor with a rated nameplate voltage of 460V should be expected to operate successfully between 414V and 506V.

Rating curve: A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station.

Raw Water: Water in its natural state, prior to any treatment for drinking.

Reagent: The chemical indicators used in testing water balance. (All the little bottles or tablets in your test kit).

Real Life Head: If you need to move the water up 30 feet, that is defined as 30 feet of head. Or if you need to have 10 PSI at the end of your pipe, that is 23.1 feet of head.

Real Power: Used strictly to develop a magnetic field within the motor.

Re-Bar: Reinforcement bar, used to add strength to a concrete. After excavation of an in ground pool, a steel cage is formed out of re-bar, and the gunite shell is shot over and surrounding it.

Recessed impeller pump: Sometimes known as vortex pump. This is a frame-mounted, back pull-out, end suction, recessed impeller, tangential discharge pump designed specifically to handle certain bulky or fibrous solids, air or gas entrained liquids or shear sensitive liquids.

Recharge Area: The land area through or over which rainwater and other surface water soaks through the earth to replenish an aquifer, lake, stream, river, or marsh. Also called a watershed.

Recharge: Water added to an aquifer. For instance, rainfall that seeps into the ground.

Rechargeable Alkaline: A variety of manganese-zinc alkaline cell designed to absorb the hydrogen gas released during recharging, and allow re-use as a secondary battery. Low in cost, but with very limited cycle lifetime

Rechargeable Battery: Any electrochemical cell or battery which can be recharged i.e., a secondary cell or battery.

Rechargeable: Capable of being recharged; refers to secondary cells or batteries.

Recharging: With secondary cells or batteries, the process of re-storing electrical energy after the battery is discharged — by driving a current back into it from an external source.

Reciprocating Pumps: Reciprocating pumps have a piston thatmoves back and forth in an enclosing cylinder.The arrangement of rotating shaft, connectingrod, and joint pushes the volume of the fluidin the cylinder through an outlet valve. The liquid enters and leaves the cylinder through check valves. Reciprocating pumps are suitable for applications where very high pressures are required, or where abrasive fluids, such as acids or viscous liquids, have to be pumped.

Recirculating System: The entire system including the suction piping, pump, strainer, filter, face piping and return piping.

Recirculation: At low flow and high flow compared to the flow at the B.E.P. the fluid will start to recirculate or move in a reverse direction at the suction and at the discharge. It is well established that cavitation type of damage Seen on the inlet vanes and not associated with inadequate NPSH can be directly linked to the pump operating in the suction recirculation zone. Similar damage Seen on the discharge vane tips can also be associated with pump operation in the discharge recirculation zone. The suction and discharge recirculation may occur at different points.

Reclaimed wastewater: Treated wastewater that can be used for beneficial purposes, such as irrigating certain plants.

Recombination: State in which the gasses normally formed within the battery cell during its operation, are recombined to form water.

Recovery (Percent Recovery): A measurement applied to distillation, reverse osmosis and ultrafiltration equipment, which characterizes the ratio of product water to feed water flow rates. The measurement is descriptive of distillation reverse osmosis or ultrafiltration equipment as a system and not of individual membrane elements. Expressed as a , recovery is defined as: % Recovery = (Product flow rate/Feed flow rate) x 100.

Recycled water: Water that is used more than one time before it passes back into the natural hydrologic system.

Reduction: A chemical process that results in the acceptance of electrons by an electrode's active material. SLA Battery: The sealed lead-acid battery is a type of secondary battery derived from the original flooded lead-acid type. It has a positive electrode of lead oxide, a negative electrode of porous metallic lead and sulphuric acid as the electrolyte.

Regeneration: Carried out using either an acid or alkali to remove the accumulated cations or anions, respectively from a filtration media. At the same time, the cation exchanger takes on hydrogen ions, to restore them to the original hydrogen or hydroxide form, respectively.

Rejection (Percent Rejection): A measure of the ability of a reverse osmosis membrane to remove salts. Expressed as a percentage, rejection is defined as: Rejection = (l-Product concentration/Feed concentration) x 100.

Relay: Electrical solenoid with heavy contacts designed to absorb high current or high amp draw , usually for motors with 3 HP or larger or used with sprinkler timers to activate a sprinkler pump. Coil voltage of solenoid may vary depending on control device, usually coil voltages come in 24V , 110V or 230V AC , amp and horsepower ratings for contacts are usually listed.

Relief Valve: Used at the discharge of a positive displacement pump. An adjustable, spring-loaded valve opens when a preset pressure is reached. Relief valves are used to prevent excessive pressure buildup that could damage the pump or motor.

Relief Valve-1-: Usually used at the discharge of a positive displacement pump. An adjustable, spring-loaded valve opens, or “relieves” when a pre-set pressure is reached. Used to prevent excessive pressure and pump or motor damage if discharge line is closed off.

Removable: Capable of being disassembled with the use of only simple tools such as a screwdriver, pliers or wrench.

Renkin scale: Used to measure low temperatures in the Fahrenheit scale. Similar to Kelvin which is used to measure low temperatures in the Centigrade system.

Repeller: A second impeller used to lower the stuffing box pressure.

Reservoir: A pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.

Residual: Usually refers to chlorine residual, or the amount of measurable chlorine remaining after treating water with chlorine. Free residual differs from combined residual in that it is not combined with ammonia or other elements or compounds, and is a more effective disinfectant.

Residual-1-: Usually refers to free available chlorine levels remaining in the pool after initial treatment or activity with contaminants.

Resilient Mounting: A suspension system or cushioned mounting designed to reduce the transmission of normal motor noise and vibration to the mounting surface. This type of mounting is typically used in fractional horsepower motors for fans and blowers.

Resin: Specially manufactured polymer beads used in the ion exchange process to remove dissolved salts from water.

Resistance:  The opposition to the flow of current in an electrical circuit. Resistance is measured in ohms.

Resistance-1-: Impedes the flow of electrons, and is measured in Ohms.

Restricted Flow: The term used to describe a condition preventing full flow of water. Restriction can occur with full skimmer or strainer baskets, obstructions in the plumbing, dirty filter, undersized plumbing or equipment, or placing devices like, heaters, cleaners or fountains in the circulation system. Restriction on the suction side creates higher vacuum, (or suction) while on the pressure side creates higher pressure.

Return flow (irrigation): irrigation water that is applied to an area and which is not consumed in evaporation or transpiration and returns to a surface stream or aquifer.

Return flow: (1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.

Return Piping: That part of the pool, spa or hot tub piping between the filter and the vessel through which filtered water passes.

Reverse osmosis: (1) (Desalination) The process of removing salts from water using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through, while the salt waste (brine) is removed and disposed. This process differs from electrodialysis, where the salts are extracted from the feed water by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. (2) (Water Quality) An advanced method of water or wastewater treatment that relies on a semi-permeable membrane to separate waters from pollutants. An external force is used to reverse the normal osmotic process resulting in the solvent moving from a solution of higher concentration to one of lower concentration.

Reynolds number: The Reynolds number is proportional to the ratio of velocity and viscosity, the higher the number (higher than 4000 for turbulent flow) the more turbulent the flow and the less viscosity has an effect. At high Reynolds numbers (See the transition line to complete turbulence in the Moody diagram) the pipe roughness becomes the controlling factor for friction loss. The lower the Reynolds number (less then 2000 for laminar flow) the more the viscosity of the fluid is relevant. Most applications are in the turbulent flow regime mode unless the fluid is very viscous (for example 300 cSt and up), the velocity has to be very low to produce the laminar flow regime.

Rheopectic: The property of a fluid whose viscosity increases with time.

Rigid shaft: Shafts with a rotating speed lower than its first critical speed.

Riparian water rights: The rights of an owner whose land abuts water. They differ from state to state and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the stream flow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on non-riparian land.

Riser: A threaded pipe used to connect a sprinkler directly to the pipe. Often used to position a sprinkler head above obstructions.

River-1-: A natural stream of water of considerable volume, larger than a brook or creek.

RMS: Root mean square. A measure of surface finish or smoothness. Metric uses C.L.A. or centerline average for the same purpose.

RO: Reverse Osmosis: the process of removing, or separating, all particles and solids down to the smallest invisible salt particle from liquids. Reverse osmosis uses intense pressure to force liquids through a membrane or filter with holes so small that no particles can get through at all, and only the pure liquid remains.

Rockwell "C": The scale most often used to measure hardness of the hard seal face.

Roller Bearing: A special bearing system with cylindrical rollers capable of handling belted applications too large for standard ball bearings.

Rotary Pumps: In rotary pumps; the impeller rotates withinan enclosing structure and imparts energyto the water. The impeller can be in the shape of a gear, screw, or lobes. For rotary pumps, the output is continuous and smoother compared to reciprocating pumps. Rotary pumps are better suited for lower pressures than reciprocating pumps because of slippage at higher pressures. Rotary pumps can jam if any solids enter the small clearance spaces between the impeller and casing. Rotary pumps are suitable for handling fluids of varying viscosities and are used in water treatment for chemical dosing.

Rotating seal: When the spring loaded or moveable portion of the seal rotates with the shaft.

Rotor Speed: Based on the frequency or hertz that the electric energy is moving. One Hertz is one complete cycle of AC electric power.

Rotor: The part of the motor that moves. It consists of a stack of metal stampings called "laminations" that are bound together, having a series of slots that may be injected with molten aluminum or wrapped with copper or aluminum wire.

Rotor-1-: The rotating member of an induction motor made up of stacked laminations. A shaft running through the center and a squirrel cage made in most cases of aluminum, which holds the laminations together, and act as a conductor for the induced magnetic field. The squirrel cage is made by casting molten aluminum into the slots cut into each lamination

RPM (Revolutions Per Minute): The number of times per minute the shaft of the motor (machine) rotates. This is a function of design and the power supply.

Rubber pump liner: See slurry pump.

Run Capacitor: Placed in line with the starting coil to smooth out the flow of electricity, making the motor run quieter by eliminating mechanical vibration caused by the turning rotor.

Run out: Twice the distance that the center of the shaft is displaced from the axis of rotation.

Runoff: (1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or ground-water runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it.

Ryznar Index: A modification of the Langelier index used to calculate the degree of calcium carbonate saturation and to predict the likelihood of scale formation from a water supply.