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CLASS 138,	PIPES AND TUBULAR CONDUITS
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SECTION I - CLASS DEFINITION

This class includes:

A. Tubular members of definite or indefinite length including wall structure of the tubular members, the end structure of the tubular members of definite length, if not elsewhere classifiable.

B. Fluid pressure compensators (e.g., accumulators or cushioning devices), flow regulators, or baffles not restricted by structure to use with any particular art.

C. Devices for thawing frozen fluid in pipes, for preventing the fluid in the pipes from freezing and for preventing the pipe from bursting if the fluid freezes.

D. Pipes with closures and plugs where tied with the structure of the pipe or limited by structure to use with a pipe.

E. Methods and apparatus for repairing pipes where not elsewhere classifiable.

SECTION II - LINES WITH OTHER CLASSES AND WITHIN THIS CLASS

For articles embracing a short length of a tube having some added feature which makes them into a shot shell, box, can or other article, the proper article class should be searched.

This class (138) includes conveyor pipes comprising the mere tube. If the device is an open chute, is more than a mere pipe, or is otherwise limited to use as a conveyor, it is classified elsewhere. See References to Other Classes below for the conveyor classes.

For tubular textile fabric for use in making hose, see Class 66, Textiles: Knitting, subclasses 169+; Class 87, Textiles: Braiding, Netting, and Lace Making, subclasses 6 and 9; Class 57, Textiles: Spinning, Twisting, and Twining, appropriate subclasses; and Class 139, Textiles: Weaving, subclasses 387+.

For pipe joints and couplings, see Class 285, Pipe Joints or Couplings. The combination of pipe wall structure and a coupling is classified in Class 285.

Methods of, and apparatus for, manufacturing tubes are not classifiable in this class but are found in the various manufacturing classes. See References to Other Classes below.

SECTION III - REFERENCES TO OTHER CLASSES

SEE OR SEARCH CLASS:

SUBCLASSES

26	WITH PRESSURE COMPENSATORS:
	This subclass is indented under the class definition.  Devices in the pipe line, attached thereto, or adapted to be attached thereto, for allowing expansion of the conducted fluid upon change in temperature, for receiving and delivering energy from and to the conducted fluid to maintain a more nearly constant pressure of the fluid and for dampening pulsations in pressure caused by a quick-shutoff of flow or by the nonuniform action of a pump. SEE OR SEARCH CLASS: 73,  Measuring and Testing,   subclass 277 for such devices tied up with the structure of a water meter or its casing, and subclasses 700+ where tied up with pressure gauges. 181,  Acoustics,   subclasses 212+ for similar structures in mufflers and sound filters. 417,  Pumps,   subclasses 540+ for such devices in combination with a significantly claimed pump.

27	Freeze protecting:
	This subclass is indented under subclass 26.  Devices intended to prevent the bursting of the pipe when the fluid therein freezes by providing an air pocket or other chamber into which the fluid can flow when it expands. SEE OR SEARCH CLASS: 123,  Internal-Combustion Engines,   subclass 41.5 for similar devices tied up with the structure of an internal combustion engine cooling system. 137,  Fluid Handling,   subclasses 59+ for fluid handling system including safety devices responsive to freeze conditions, subclasses 301+ for hydrants having means for preventing freezing, subclasses 334+ for fluid handling devices including heating means to prevent freezing, subclass 375 for jacketed or insulated fluid handling apparatus, and subclass 593 for fluid distribution systems provided with expansion chambers.

28	Expansible or compressible tube element:
	This subclass is indented under subclass 27.  Devices in which the tube itself or a part thereof is expansible or an element in the tube is compressible to allow for the expansion of the fluid when it freezes.

30	Variable capacity chambers:
	This subclass is indented under subclass 26.  Devices in the form of a chamber whose capacity is variable usually by means of a flexible diaphragm or sliding plunger. SEE OR SEARCH CLASS: 239,  Fluid Sprinkling, Spraying, and Diffusing,   subclasses 89 and 96 for accumulator chambers which store fluid under pressure for subsequent delivery to a nozzle.

31	Piston or plunger type:
	This subclass is indented under subclass 30.  Devices in which the chamber is of variable capacity by reason of a slidable piston or plunger.

32	THAWING AND FREEZE PROTECTION:
	This subclass is indented under the class definition.  Devices for thawing the frozen fluid in pipes or pipes having means for preventing the fluid from freezing or for preventing the bursting of the pipe when the fluid freezes. SEE OR SEARCH THIS CLASS, SUBCLASS: 27+, where the device allows for the expansion of the fluid. SEE OR SEARCH CLASS: 73,  Measuring and Testing,   subclass 277 for similar devices tied up with the structure of a water meter or its casing. 123,  Internal-Combustion Engines,   subclass 41.5 for similar devices tied up with the structure of an internal combustion engine cooling system. 137,  Fluid Handling,   subclasses 59+ for fluid handling systems including safety devices responsive to freeze conditions, subclass 107 for drain or waste valves responsive to the stopping of the main line flow, subclasses 301+ for hydrants having means for preventing freezing, subclasses 334+ for fluid handling devices including heating means to prevent freezing, subclass 375 for jacketed or insulated fluid handling apparatus, and subclass 596 for stop and waste devices. 165,  Heat Exchange,   subclass 134.1 for a heat exchanger with a protector. 237,  Heating Systems,   subclass 80 for similar devices tied up with a heating system.

33	Electric:
	This subclass is indented under subclass 32.  Devices which are in the form of an electric heater. SEE OR SEARCH CLASS: 219,  Electric Heating,   subclass 535 for the electric heaters, per se, adapted for use in thawing pipes.

34	Anti-freeze substance:
	This subclass is indented under subclass 32.  Devices which have means for putting an antifreeze substance into the fluid in the pipe. SEE OR SEARCH CLASS: 48,  Gas: Heating and Illuminating,   subclass 190 for the addition of combustible, antifreeze solutions to gaseous fuels. 252,  Compositions,   appropriate subclasses for antifreeze compounds.

35	Portable thawing apparatus:
	This subclass is indented under subclass 32.  Thawing apparatus which is portable and not elsewhere classifiable as a stove or heater.

36	WITH WEAR INDICATOR:
	This subclass is indented under the class definition.  Pipes having means whereby they will be caused to leak when worn so as to need replacing and other wear indicating means.

37	WITH FLOW REGULATORS AND/OR BAFFLES:
	This subclass is indented under the class definition.  Pipes or pipe fittings having baffles or other means for changing the direction or rate of flow of fluid in the pipe or for governing the degree of turbulence of the flowing fluid. SEE OR SEARCH CLASS: 48,  Gas: Heating and Illuminating,   subclasses 180+ for conduits having mixing means for fuel gases. 110,  Furnaces,   subclasses 324+ for baffles or heat retainers structurally defined for engaging pipe structure. 137,  Fluid Handling,   appropriate subclasses for processes and apparatus having means for controlling the flow of fluid therein and multiple valves, per se, particularly subclasses 98+ for baffles employed for securing self-proportioning flow, subclass 505+ for pressure regulators where the regulation is varied by the pressure in the pipe, subclass 574 for baffles employed to form plural compartments for serial flow, and subclasses 610+ for deflectors forming a flow control device at the junction of a plurality of flow passages. 181,  Acoustics,   subclasses 212+ for similar structures in mufflers and sound filters. 251,  Valves and Valve Actuation,   appropriate subclasses for valves where the flow may be shut off, particularly subclasses 118+ (and the search notes thereto) for other fluid handling devices with baffles or other material guide structure. 406,  Conveyors: Fluid Current,   subclass 92 for conduit having means to create whirling motion in a conveying fluid current; subclasses 155+ for proportional flow distributors; and subclasses 191+ for a conduit having a flow regulator or baffle therein, and some structural feature peculiar to the conveying of solids in a fluid current.

38	Heat transfer:
	This subclass is indented under subclass 37.  Pipes in which the baffle or other means is designed to facilitate a transfer of heat between fluids inside and outside of the pipe. SEE OR SEARCH CLASS: 165,  Heat Exchange,   subclasses 177+ for a pipe or tubular conduit limited by structure on its exterior for use as a heat exchanger, particularly subclass 181+ for such an element with exterior fins.

39	Flow facilitating:
	This subclass is indented under subclass 37.  Pipes in which the baffles or other means are designed to facilitate the flow of fluid in the pipe.

40	Restrictors:
	This subclass is indented under subclass 37.  Pipes in which the means restricts the flow in the pipe, but does not cut off entirely. (1) Note. This subclass and the indented subclasses include some devices disclosed for the purpose of forming a mixture or emulsion of a plurality of fluids but in which the claims are limited to the structure of the conduit and the flow restrictor. See the Search Class Notes below. SEE OR SEARCH CLASS: 62,  Refrigeration,   subclasses 511 and 527+ for restrictors tied up with a refrigerating system. 73,  Measuring and Testing,   subclass 707 for restrictors for protecting gages and claimed in combination therewith or otherwise tied up with the gage structure, and subclasses 861.42+ where the restrictor is tied up with connections to a flow meter. 99,  Foods and Beverages: Apparatus,   appropriate subclasses for apparatus other than a mere mixer, for treating foods and beverages and not elsewhere provided for. See the (1) Note above. 166,  Wells,   subclass 91.1 for well head apparatus with chokes or beans. 184,  Lubrication,   subclasses 6+ and subclass 52 for restrictors tied up with a lubricating system. 210,  Liquid Purification or Separation,   subclass 118 for the combination of a separator and a variable restrictor responsive to a condition, subclasses 418+ for a filter and flow controller combination, and subclasses 435+ for strainers in pipes which incidentally restrict. 241,  Solid Material Comminution or Disintegration,   appropriate subclasses for apparatus for forming suspensions of solids in liquids. See the (1) Note above. 366,  Agitating,   subclasses 336+ for mixing devices having features additional to merely a conduit and flow restrictor for effecting agitation in a liquid flowing therethrough, and subclasses 176.1+ for a similar device including force applying feed means to effect emulsification. See the (1) Note above. 516,  Colloid Systems and Wetting Agents; Subcombinations Thereof; Processes of Making, Stabilizing, Breaking, or Inhibiting,   subclasses 9+ for colloid systems of liquid continuous phase (e.g., emulsions, suspensions, dispersions, foams) or agents for such systems or making or stabilizing such systems or agents, when generically claimed or when there is no hierarchically superior provision in the USPC for the specifically claimed art.

41	With screen:
	This subclass is indented under subclass 40.  Pipes which have a screen in the line of flow in addition to the restrictor.

42	Tortuous path:
	This subclass is indented under subclass 40.  Devices in which the path of flow of the fluid is tortuous.

43	Variable restriction:
	This subclass is indented under subclass 42.  Devices wherein the device is adjustable to vary the restriction.

44	Central path:
	This subclass is indented under subclass 40.  Devices in which the path of flow of the fluid is centrally of the tube.

45	Variable restriction:
	This subclass is indented under subclass 44.  Devices wherein the restrictor is adjustable to vary the restriction. SEE OR SEARCH CLASS: 239,  Fluid Sprinkling, Spraying, and Diffusing,   subclasses 408+ and 451+ for spray nozzles having adjustable restrictions. 396,  Photography,   subclass 64 for camera diaphragms.

46	Variable restriction:
	This subclass is indented under subclass 40.  Devices in which the restrictor is adjustable to vary the restriction.

89	WITH CLOSURES AND PLUGS:
	This subclass is indented under the class definition.  Subject matter relating to pipes or pipe fittings having closures or plugs, or closures and plugs limited by structure to use with pipes. SEE OR SEARCH THIS CLASS, SUBCLASS: 98+, for patches. SEE OR SEARCH CLASS: 4,  Baths, Closets, Sinks, and Spittoons,   subclasses 286+ for bath, closet, and sink closures. 89,  Ordnance,   subclass 31 for plugs or other devices for closing the gun-muzzle or other opening in the barrel of a gun. 122,  Liquid Heaters and Vaporizers,   subclasses 360+ for closures and couplings for water tube boilers. 137,  Fluid Handling,   subclasses 247.11+ for liquid seals including access openings and closures therefor, especially subclasses 247.47 and 247.51. 156,  Adhesive Bonding and Miscellaneous Chemical Manufacture,   subclasses 294 and 423 for processes and apparatus for inserting a core within a tube in combination with a laminating step. 166,  Wells,   subclasses 75.11+ for well head closures having some fluid handling feature and subclasses 192+ and the subclasses there noted for plugs inserted into a prepositioned well conduit. 174,  Electricity: Conductors and Insulators,   subclasses 20 , 22, and 23 for fluid stops associated with electrical conduits, cables, end structures or joints. 202,  Distillation: Apparatus,   subclasses 242+ for closures for distillation apparatus. 215,  Bottles and Jars,   subclasses 37+ for closures for bottles and jars. 217,  Wooden Receptacles,   subclasses 56+ , 76+, and 98+ for closures for wooden receptacles. 220,  Receptacles,   subclasses 200+ for closures and plugs having a more general use. 285,  Pipe Joints or Couplings,   subclass 126.1 for couplings having an access opening with closure means. 405,  Hydraulic and Earth Engineering,   subclass 42 for an end closure for irrigation or drainage conduit.

89.1	Air and dust cap:
	This subclass is indented under the unnumbered subclass Inflation stem type.  Closures for pipes of the inflation stem type comprising an air cap which closes the end of the pipe and a dust cap which shrouds the air cap and a portion of the pipe. SEE OR SEARCH CLASS: 137,  Fluid Handling,   subclasses 232+ for inflation stems combined with cap or closure for protecting and/or sealing the end thereof. 152,  Resilient Tires and Wheels,   subclass 428 for one or both of the caps combined with the inflation stem and the attachment to the wheel, rim, felly, or tire.

89.2	Combined:
	This subclass is indented under subclass 89.1.  Closures in which the air cap and dust cap are combined in one structure.

89.3	Air cap:
	This subclass is indented under the unnumbered subclass Inflation stem type.  Closures for pipes of the inflation stem type comprising air caps. SEE OR SEARCH CLASS: 152,  Resilient Tires and Wheels,   subclass 431 for combined caps and deflating tools.

89.4	Dust cap:
	This subclass is indented under the unnumbered subclass Inflation stem type.  Closures for pipes of the inflation stem type comprising dust caps.

90	Test plugs:
	This subclass is indented under subclass 89.  Plugs for pipes having provisions whereby a fluid may be introduced into the pipe through the plug or for the attachment of a gauge for the purpose of testing the pipe for leaks.

91	Double end:
	This subclass is indented under subclass 89.  Plugs for pipes wherein both ends of the pipe are plugged by connected plugs.

92	Lateral opening:
	This subclass is indented under subclass 89.  Closures and plugs designed to close an opening in the side of a pipe.

93	Inflatable:
	This subclass is indented under subclass 89.  Plugs for pipes having an inflatable member to seal against inside of the pipe opening.

94	Laterally insertable:
	This subclass is indented under subclass 89.  Closures and plugs for the inside opening of a pipe which are insertable through a lateral opening in the pipe.

94.3	Line blinds:
	This subclass is indented under subclass 94.  Closures of the type generally known as "line blinds" which are of platelike form. (1) Note. These devices differ from valves in that they have no surrounding housing to prevent leakage of fluid when the closure and seat are moved relative to each other. SEE OR SEARCH THIS CLASS, SUBCLASS: 44+, for line blinds combined with flow restrictors. SEE OR SEARCH CLASS: 251,  Valves and Valve Actuation,   subclasses 167+ , 193+, and 326+ for reciprocating gate valves, and see (1) Note above.

94.5	Pivoted:
	This subclass is indented under subclass 94.3.  Closures in which the plates are pivoted. SEE OR SEARCH CLASS: 251,  Valves and Valve Actuation,   subclasses 177+ and 301+ for pivoted gate valves.

95	Return bend type:
	This subclass is indented under subclass 89.  Closures and plugs specially designed to be used with a return bend fitting. SEE OR SEARCH CLASS: 122,  Liquid Heaters and Vaporizers,   subclass 360 for return bend fittings, for boilers combined with the connection to the tubes and the closures. 285,  Pipe Joints or Couplings,   subclasses 135.1+ for return bend fittings.

96	END PROTECTORS:
	This subclass is indented under the class definition.  Devices for protecting the ends of pipes, usually threaded, from damage when not in use while being shipped or handled. SEE OR SEARCH CLASS: 16,  Miscellaneous Hardware,   subclasses 2.1+ and 108+ for thimbles.

97	REPAIRING:
	This subclass is indented under the class definition.  Processes and apparatus for repairing leaks in pipes and hose and not otherwise classifiable. SEE OR SEARCH CLASS: 81,  Tools,   subclasses 15.2+ for tire repairing tools. 137,  Fluid Handling,   subclasses 15.08 through 15.17for a process of securing, replacing, or servicing a pipe, joint, valve, or tank; or subclasses 315.01-329.4 for a fluid handling system with repair, tapping, assembly, or disassembly means. 249,  Static Molds,   subclasses 83+ , particularly subclass 90 for molds for repairing leaks in pipes. 405,  Hydraulic and Earth Engineering,   subclass 154.1 for a process or apparatus of subterranean or submarine pipe or cable laying, retrieving, manipulating, or treating; subclass 184.1 for repairing, replacing, or improving a pipe or cable while in a subterranean or submarine location; and subclass 188 for an apparatus or method for enabling personnel to work on a section of submerged pipeline. 425,  Plastic Article or Earthenware Shaping or Treating: Apparatus,   subclasses 11+ for a product or preform repair or restoring means comprising a molding apparatus for shaping or reshaping nonmetals.

98	Patches:
	This subclass is indented under subclass 97.  Subject matter relating to patches for leaky pipes or hose. SEE OR SEARCH CLASS: 114,  Ships,   subclasses 227+ for leak stoppers for ships. 152,  Resilient Tires and Wheels,   subclasses 367+ for pneumatic tire patches. 220,  Receptacles,   subclasses 243+ for patches for metal pipe which are inserted through an openi