Galvanic Action
Corrosion of two unlike metals due to electrical current passing between them. The action is increased in the presence of moisture.
Gas
Vapor phase of a substance.
Gas, noncondensable
Gas that will not form into a liquid under the operating pressure-temperature conditions.
Gas valve
Device in a pipeline for starting, stopping, or regulating the flow of gas.
Gasket
Resilient (spongy) or flexible material used be between mating surfaces to give a leakproof seal.
Gauge, compound
See Compound gauge.
Gauge, high-pressure
Instrument for measuring pressures in the range of 0 psig to 500 psig (101.3 kPa to 3 600 kpa).
Gauge, low-pressure
Instrument for measuring pressures in range of 0 psia to 50 psia (0 kPa to 350 kPa.
Gauge, manifold
Chamber device constructed to hold both compound and high-pressure gauges. Valves control the flow of fluids through it.
Gauge port
Opening or connection provided for installing a gauge.
Gauge vacuum
Instrument used to measure pressures, below atmospheric Pressure.
Generator
In an absorption system, the component in which the ammonia-water mixture is heated.
Geothermal
An underground or underwater temperature source used for the operation of a heating cooling system (heat pump).
Geothermal Heat Pump
A heat pump that uses the constant underground or underwater temperature supply.
Glycol Water Solution forced-air furnace
Furnace with 50% glycol and 50% distilled water solution, which passes through a tube-and-fin heat exchanger to distribute heat through the furnace duct system.
Grain
Unit of weight equal to 1/7000 lb., used to indicate the amount of moisture in the air.
Gravity Air
Air that naturally rises when heated and flows through warm air ducts. When it cools, it becomes denser (heavier) and flows down.
Gravity flow
The tendency of liquids to flow downward and rest at the lowest possible point.
Gravity Heating
Heating system in which heated air is distributed by natural rising (no fans are used for circulation).
Grille
Ornamental or louvered opening placed in a room at the end of an air passageway.
Grommet
Plastic, metal, or rubber doughnut-shaped protectors, which line holes where wires or tubing pass through panels.
Ground, short circuit
Fault in an electrical circuit allowing electricity to flow into the metal parts of a mechanism.
Ground Coil
Heat exchanger buried in the ground. May be used either as an evaporator or as a condenser.
Ground Wire
Electrical wire that will safely conduct electricity from a structure into the ground.
Gun burner
Furnace burner that atomizes oil by pushing it through an orifice, into the combustion chamber.