| http://www.w3.org/ns/prov#value | - The upper portion of the plug valve 90 may be provided with a groove 94 for an O-ring 96 and have in its outer exposed end a slot 98 by which a screwdriver or other tool may be used for rotating the beveled plug 90 for shutting off or permitting more or less of the fluid to be returned to the outlet duct 34 via ducts 77, while the rest of the fluid flows around the narrowed portion of the plug 90
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