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Vacuum Wall Fitting: The fitting in the wall of the pool just below the water level to which is attached the hose for the underwater suction cleaner.

Vacuum: A measure of pressure below atmospheric pressure. When the impeller rotates, it creates a vacuum in the eye of the impeller, which allows atmospheric pressure to push the water into the vacuum.

Vacuum-1-: Any pressure less than atmospheric. Can present a problem for the elastomer in many seal applications.

Vacuum-2-: Refers to the low pressure condition created in the suction line. Also refers to the cleaning process of sucking leaves, algae and debris from the pool floor.

Vacuum-3-: Pressure less than atmospheric pressure.

Valves: A device placed in the plumbing line which restricts or obstructs water flow to create desired hydraulics, or may permit flow in one direction only (as in a check valve).

Valves-1-: Check Valve: Allows liquid to flow in one direction only. Generally used in discharge line to prevent reverse flow.

Vane pass frequency: When doing a vibration analysis this frequency (no. of vanes times the shaft speed) and it's even multiples shows up as a peak which can indicate a damaged or imbalanced impeller.

Vane passing syndrome: A type of cavitation caused by the impeller/ cutwater clearance being too small.

Vane pump (hydraulic): A positive displacement pump. Vane pumps are used successfully in a wide variety of applications (See below). Because of vane strength and the absence of metal-to-metal contact, vane pumps are ideally suited for low-viscosity, non lubricating liquids up to 2,200 cSt / 10,000 SSU. Such liquids include LPG, ammonia, solvents, alcohol, fuel oils, gasoline, and refrigerants.

Vaned Diffuser: Has gradually expanding passageways all the way around.

Vapor pressure: Below this pressure, the liquid at this temperature will vaporize.

Vapor Pressure: The pressure that is required to keep water in a liquid state at that temperature.

Vapor pressure-1-: the pressure at which a liquid boils at a specified temperature.

Vaporize: The fluid passes from a liquid to a gaseous state. If this happens at the seal faces the seal faces will be blown open.

Variable Frequency Drive (VFD): Circuitry that runs a motor from 0 to 60 Hz.

Variable High-Speed Drive (VSD): Circuitry that runs a motor from 30 to 80 Hz.

Variable speed motor: Used to control flow in a system by varying the frequency of the motor. Recommended for circulating systems and any other system where the main head is friction losses in the piping system.

Variable speed motor: Used to control flow in a system by varying the frequency of the motor. Recommended for circulating systems and any other system where the main head is friction losses in the piping system.

Variable Torque Pump: The torque required is proportional to rotational velocity of the impeller.

Variance: State or EPA permission not to meet a certain drinking water standard. The water system must prove that: (1) it cannot meet a MCL, even while using the best available treatment method, because of the characteristics of the raw water, and (2) the variance will not create an unreasonable risk to public health. The State or EPA must review, and allow public comment on, a variance every three years. States can also grant variances to water systems that serve small populations and which prove that they are unable to afford the required treatment, an alternative water source, or otherwise comply with the standard.

Velocity Head difference: the difference in velocity head between the outlet and inlet of the system.

Velocity Head: A measurement of the amount of energy in water due to its velocity or motion.

Velocity Head-1-: Part of the total head calculation. Derived from the formula h = V2/2g

Velocity: A measurement of the speed of the liquid in the system. Measured in feet or meters per second. The pump is a constant velocity device.

Velocity-1-: The measurement of the motion of liquids, expressed in feet per second.

Vent: A normally sealed mechanism that allows for the controlled escape of gases from within a cell.

Vent-1-: To remove air or gas from the system. It is important to vent the stuffing box in vertical pumps to prevent the seal faces from running dry.

Venturi (Bernoulli's law): A venturi is a pipe that has a gradual restriction that opens up into a gradual enlargement. The area of the restriction will have a lower pressure than the enlarged area ahead of it. If the difference in diameters is large you can even produce a very high vacuum (-28 feet of water). I use a cheap plastic venturi made by Fisher or Cole Palmer for an experiment that I do to demonstrate vapor pressure during my training seminars and it is very easy to create very high absolute vacuum. Bernoulli's law is a relationship between two points within a system that states that the sum of the energies that correspond to pressure, velocity and elevation must be conserved.

Venturi or Venturi Tube: A tube having a constricted throat which causes differences in pressure and can be used to operate feeding devices, instruments and to measure flow. When used in conjunction with a nozzle, it converts the velocity of the liquid being pumped to pressure.

Venturi: Increasing water velocity by restricting pipe size usually accomplished by a spa jet.

Vermiculite: A natural mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed items. Vermiculite is formed by hydration of certain basaltic minerals.

Vertical Lift: The distance between the pumping level of the well and the center line of the pump, expressed in feet.

Vertical Turbine Pumps:In vertical turbine pumps, the water flowsvertically through a channel of uniformcross-sectional area. The impeller is positionedin the center along the axis in thechannel. The blades of the impeller are shaped so that the water flows in a radialdirection. The casing has diffuser vanes, shaped so that they guide water and make it flow either into the discharge or through diffuser bowls into inlets of succeeding stages. Vertical turbine pumpsare used most often at raw water intakes and at booster stations in the distribution systemto augment the pressure required for service. Vertical turbine pumps are relatively moreexpensive than centrifugal pumps for the same capacity and require more maintenance.

Vertical Wall: Shall refer to the wall up to a positive 11° angle towards the pool’s interior from plumb.

Vibration Damping: Important in metal bellows seal designs. The elastomer acts as a vibration damper in the other seals. The vibration can chip carbon faces, destroy anti-rotation drive lugs, and open the lapped seal faces.

Vinyl Liner: One type of interior pool finish. The liner is draped over a sand or cementitious floor, and locked into the top of the pools wall.

Violation: A failure to meet any state or federal drinking water regulation.

Virus: The smallest infectious microorganism, made of RNA or DNA, in a protein shell, which grow only in other, living cells. They are 0.004 to 0.1 microns in size and about 100 times smaller than bacteria.

Viscosity: A property from which a fluid's resistance to movement can be evaluated. The resistance is caused by friction between the fluid and the boundary wall and internally by the fluid layers moving at different velocities. The more viscous the fluid the higher the friction loss in the system. Centrifugal pumps are affected by viscosity and for fluids with a viscosity higher than 10 cSt, the performance of the pump must be corrected. The basic unit of viscosity is known as the Poise or centiPoise (cP) named after the French scientist Poiseuille who discovered a practical method of measuring viscosity. The greek letter is used to represent viscosity. There are two types of viscosity, the first just mentioned is known as absolute viscosity and the other for which the greek letter nu is used is called the kinematic viscosity. The unit of kinematic viscosity is the centiStoke (cSt) named after the English scientist Stokes.

Viscosity-1-: Resistance to pouring. Higher viscosity can restrict seal movement. Centrifugal pumps can handle a maximum viscosity similar to 30-weight oil at room temperature. Above this viscosity a positive displacement pump should be used.

Viscosity-2-: The resistance of a fluid to flowing freely, caused by friction from its molecules OR a measure of how strongly molecules cling to each other. The higher the viscosity of the liquid, the higher the resistance to flow and the greater the head loss.

Viscosity-3-: A property, which measures a fluid's resistance to movement. The resistance is caused by friction between the fluid and the boundary wall and internally by the fluid layers moving at different velocities.

Viscosity-4-: The thickness of a liquid, or its ability to flow. Temperature must be stated when specifying viscosity, since most liquids flow more easily as they get warmer. The more viscous the liquid, the slower the pump speed required.

Viscous drag pump: A pump whose impeller has no vanes but relies on fluid contact with a flat rotating plate turning at high speed to move the liquid.

Vision System: Is the technology which isolates nascent oxygen into a powerful sanitizing tool. See Cationic Sanitation.

Viton: Is a registered trademark of the DuPont Company. Viton is the most specified fluoroelastomer, well known for its excellent (400°F/200°C) heat resistance. Viton offers excellent resistance to aggressive fuels and chemicals and has worldwide ISO 9000 and ISO/TS 16949 registration.

Viton-1-: Viton is a brand of synthetic rubber and fluoropolymer elastomer. It is generally resistant to many acids and some solvents, has good high temperature properties up to 180º F but poor low temperatures performance.

Viton®-2-: An E.I. Dupont Dow manufactured elastomer widely used in the sealing industry. The generic name is fluorocarbon. Water and steam attack many of these compounds.

VOC or Volatile Organic Compound: A category of water contaminants.

Volt: A unit of measurement that indicates the amount of voltage in a circuit.

Voltage drop: Loss encountered across a circuit impedance from power source to applicable point (motor) caused by the resistance in conductor. Voltage drop across a resistor takes the form of heat released into the air at the point of resistance.

Voltage drop-1-: The amount of voltage that exists across two points of an electrical circuit.

Voltage Loss: The amount of electricity used to force current(amps) to where it needs to go. This can be caused various ways such as too small of wire, too long of a run, etc.

Voltage, cutoff: Voltage at the end of useful discharge. (See Voltage, end-point.)

Voltage, end-point: Cell voltage below which the connected equipment will not operate or below which operation is not recommended.

Voltage, nominal: Voltage of a fully charged cell when delivering rated current.

Voltage: Electric potential similar to pressure but not a form of energy.

Voltage-1-: The electrical force or pressure that causes current to flow in a circuit. Voltage is measured in volts.

Volts: An electrical measurement of motor performance where voltage(volts) = current(amps) x resistance(ohms). Volts measures the pressure of electricity.

Volume: The amount that something will hold OR the contents of a space that is formed by lines that can be measured in three directions (length x width x height). In a pipe the formula is (Area x length).

Volute Case: A pump component that encloses the impeller and converts the high velocity energy created by the impeller into pressure energy. It is spiral shaped, similar to a snail's shell.

Volute casing: Derives is name from a spiral shaped casing surrounding the pump impeller. It converts velocity energy to pressure energy.

Volute: A stationary housing inside the pump housing in which the impeller rotates. It is used to separate air and water.

Volute-1-: A volute is a curved funnel increasing in area to the discharge port. It is often used with impeller pumps. As the area of the cross-section increases, the volute reduces the speed of the liquid and increases the pressure of the liquid. One of the main purposes of a volute casing is to help balance the hydraulic pressure on the shaft of the pump. However, this occurs best at the manufacturer's recommended capacity. Running volute-style pumps at a lower capacity than the manufacturer recommends can put lateral stress on the shaft of the pump, increasing wear-and-tear on the seals and bearings, and on the shaft itself.

Volute-2-: The casing surrounding the impeller in a centrifugal pump that collects the liquid discharged from the impeller.

Vortex Impeller: Special class of semi-open impeller that creates a vortex in the water and spins the solids to the outside of the water vortex. A vortex impeller stands away from the pump volute case in order to pass solids. Special advantage of a vortex impeller is that it is not prone to clogging with stringy material. does not allow solids to pass through the impeller but forms a whirlpool under the impeller which moves solids up and away.

Vortex Pump: A type of pump used for excessive solids. The impeller is recessed into the volute. A very low efficiency design, but practical in many applications.

Vortex: See submersion.

Vortexing liquid: Creating a "whirlpool affect" that can draw air into the suction of the pump.

Vulnerability Assessment: An evaluation of drinking water source quality and its vulnerability to contamination by pathogens and toxic chemicals.