Galling: The tearing of metal surfaces when two elements rub against each other. Usually caused by lack of lubrication or extreme contact pressure of materials of a similar hardness value.
Gas: A compressible fluid – such as air, hydrogen, nitrogen, etc.
Gasket: A component whose purpose is to seal a joint between two larger components, softer than the surfaces of the joint being sealed and usually squeezed by means of bolting to effect the seal.
Gate Valve: A straight-thru pattern valve whose closure element is a wedge, situated between two fixed seating surfaces, with means to move it in or out of the flow stream in a direction perpendicular to the pipeline axis.
Gate: The closure member of a gate valve (sometimes called wedge).
Gland: That part of a valve which retains or compresses the stem packing. Sometimes manually adjustable.