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Gage height: The height of the water surface above the gage datum (zero point). Gage height is often used interchangeably with the more general term, stage, although gage height is more appropriate when used with a gage reading.

Gaging station: A site on a stream, lake, reservoir or other body of water where observations and hydrologic data are obtained. The U.S. Geological Survey measures stream discharge at gaging stations.

Galvanic Action: Creation of an electrical current by electrochemical action.

Galvanic Cell: A combination of electrodes, separated by electrolyte, that is capable of producing electrical energy by electrochemical action. An electrochemical cell which employs a chemical reaction to generate electrical energy. The first such cell is attributed to Luigi Galvani in 1792 — although Alessandro Volta was the first to explain how it worked, in 1800.

Galvanic Corrosion: Galvanic corrosion occurs when two different types of metals are put into physical contact with each other while they are immersed in an electrolyte, such as seawater. The reason corrosion takes place between two different, coupled metals is that a voltage difference (potential) exists between them. For example, many mid-sized sailboat propulsion shafts are made of 300 series stainless steel, which possesses an average voltage of -0.07V. These sailboat shafts are frequently connected to bronze propellers, which possess an average voltage -0.26V. The voltage difference between these two coupled metals is approximately .19V. The most successful method in protecting both metals is to connect both of them to a third metal that is more anodic than the original coupled metals. In this case, the third metal becomes a “sacrificial anode” and the two original metals will remain passive.

Galvanic series: Lists of metals with those on the top of the list being attacked by those lower down in the list. The father apart on the list, the faster the attack.

Galvanic series: Lists of metals with those on the top of the list being attacked by those lower down in the list. The father apart on the list, the faster the attack.

Gas Or Air Entrainment: The entrapment of localized gas or air bubbles and pockets that are created at the discontinuity between an impinging jet flow and the receiving pool of water.

Gas Valve: An electronic valve in the pool heater that directs gas flow from the meter to the pilot and the burner tray.

Gasket or O-Ring: A plastic or rubber ring or flat plastic or paper device used in machinery as a seal against air, oil, or high pressure.

Gasket: A gasket is a mechanical seal that fills the space between two objects, generally to prevent leakage between the two objects while under compression. Gaskets are commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicone, metal, or a plastic polymer.

Gasket-1-: Used between two static surfaces to provide a seal. Made from a variety of deformable materials.

Gassing: The evolution of gas from one or both of the electrodes in a cell. Gassing commonly results from self-discharge or from the electrolysis of water in the electrolyte during charging.

Gate Valve: The gate valve, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are used when a straight-line flow of fluid and minimum restric-tion is desired. The gate faces can form a wedge shape or they can be parallel. Gate valves are primarily used to permit or prevent the flow of liquids, but typical gate valves shouldn't be used for regulating flow, unless they are specifically designed for that purpose.

Gate Valve-1-: This is probably the least effective of all the valves as it is more prone to cavitation damage and can easily be adjusted by the end user.

Gauge Pressure (PSIA): Pressure above atmospheric pressure.

Generator:  A machine with a rotating component that converts mechanical energy into electrical energy.

Generator-1-: A device used to create electrical energy. When operating, a generator will cause a flow of electrical charge.

Geolast: Geolast: suitable for light fraction hydrocarbons and solvents. Buna and Geolast have similar chemical.

Geyser: A geothermal feature of the Earth where there is an opening in the surface that contains superheated water that periodically erupts in a shower of water and steam.

Giardia Lamblia: A microorganism frequently found in rivers and lakes, which, if not treated properly, may cause diarrhea, fatigue, and cramps after ingestion.

Giardiasis: A disease that results from an infection by the protozoan parasite Giardia Intestinalis, caused by drinking water that is either not filtered or not chlorinated. The disorder is more prevalent in children than in adults and is characterized by abdominal discomfort, nausea, and alternating constipation and diarrhea.

Glacier: A huge mass of ice, formed on land by the compaction and re-crystallization of snow, that moves very slowly down slope or outward due to its own weight.

Gland: A groove made to hold the o-ring seal so that desired compression for proper sealing is maintained.

Gland-1-: The part that holds one half of the mechanical seal and attaches to the stuffing box.

Glandless pumps: Is an ordinary centrifugal or turbine pump with no stuffing box or end seals. Dynamic sealing is replaced by static housing (shell) separating the flow—through part of the pump and the power—driven electric motor. The torque from the electric motor is transmitted to the pump shaft through the sealing shell by magnetic coupling (based on permanent magnets) consisting of the driving and driven half—couplings attached to the shaft of the electric motor and pump.

Glauconite Sand: A mineral which is frequently used in depth filters.

Governor: A device that maintains a constant engine speed; a spring loaded device which is mounted under the canopy on the motor shaft designed to regulate rotational speed or momentum.

GPD-Gallons Per Day: A flow rate measurement.

GPG - Grains Per Gallon: Equivalent to 17.1 milligrams/liter of calcium carbonate.

GPH: Gallons per hour of fuel consumption.

GPM/GPH: Used to express the number of gallons per minute or gallons per hour produced by a pump or capacity requirements for residential usage.

GPM: Gallons per minute is a water measure of both the water source and the sprinkler's delivery rate.

GRAPHITE:  Graphite is the packing and seal material of choice for most fire-rated products, primarily because of its high temperature rating of approximately 2000°F. Graphite has excellent chemical resistance, can retain compressibility at all temperatures and has a low coefficient of friction. Graphite is not recommended for use in strong oxidizing atmospheres.

Grates and Anti-Vortex Covers: Protective covers for the main drains. Each main drain must have a cover that is IAPMO* certified to be of anti-entrapment and anti-hair-entanglement design, and rated for the flow that it must handle. It must be correctly installed with screws. Operating a pool without proper covers on the main drains is extremely dangerous.

Gratuitous Harmonics: Annoying and potentially harmful signals generated by variable frequency drives (VFD) that are transmitted into a dwellings electrical network. Modern VFD devices use improved power components to minimize this effect.

Gravity Feed Systems: These private systems use gravity as the means to move the water from one side of tank to the other or from the septic tank to the effluent tank and then to final dispersal.

Gray Iron:  An alloy of iron, carbon and silicon; easily cast; good pressure tightness in the as-cast condition. Gray iron has excellent dampening properties and is easily machined. It is standard material for bodies and bonnets of Class 125 and 250 iron body valves. Gray iron has corrosion resistance that is better than steel in certain environments.

Gray Water: Non-toilet household wastewater (sinks, showers, laundry, etc.) that is sometimes recycled especially for use in gardening or for flushing toilets.

Grease seal: A spring-loaded elastomer seal commonly used to seal bearings. Sometimes called a "lip seal". Not a good choice for sealing the bearing casing of a pump. A labyrinth or face seal would be a better choice.

Greywater: Waste water from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks.

Grinder Pump: A sewage pump designed to chop or cut solids, which are mixed with the water to become slurry.

Ground water, confined: Ground water under pressure significantly greater than atmospheric, with its upper limit the bottom of a bed with hydraulic conductivity distinctly lower than that of the material in which the confined water occurs.

Ground water, unconfined: Water in an aquifer that has a water table that is exposed to the atmosphere.

Ground water: Surface water that seeps down through the earth and accumulates in porous material at subsurface level.

Ground Water-1-: The water that systems pump and treat from aquifers (natural reservoirs below the earth's surface).

Ground water-2-: Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust.

Ground-Fault Circuit-Interrupter (GFI): A device to interrupt the power supply to a piece of equipment when it senses very small electrical leaks to the ground or to the pool water. It will cut off power in dangerous circumstances which might not cause a circuit breaker to trip or a fuse to blow.

Ground-water recharge: Inflow of water to a ground-water reservoir from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.

Grout: A construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints (like those between tiles). Grout is generally composed of a mixture of water, cement, sand and sometimes color tint which is applied as a thick liquid and hardens over time, much like mortar.

Gunite: A dry mixture of cement and sand mixed with water at the "gun"; hence the name. A Gunite operator "shoots" the pool's rough shape, while finishers trowel after.

Gutter Fitting (Gutter Drain): A drainage fitting used in the overflow gutter.