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 [Search a list of Patent Appplications for class 251]   CLASS 251,VALVES AND VALVE ACTUATION
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SECTION I - CLASS DEFINITION

This class provides for means, for regulating flow of a fluid through a passage, either by closing the passage or restricting it by a definite predetermined motion of the closing-element, that are of general application not otherwise provided for.

SECTION II - LINES WITH OTHER CLASSES AND WITHIN THIS CLASS

A valve is distinguished from a closure of the cap type by being shiftable between open and closed position in the device rather than bodily removable from it, but pivoted closures and many pivoted valves have no definable difference. For this reason, closures associated with valves have been grouped with plural valves in certain parts of Class 137, Fluid Handling.

See the Class Definition of Class 137, Fluid Handling, References to Other Classes, for collected search notes on automatic valves, plural valves and their actuators, and manual valve actuation, selection, and/or adjusting.

SECTION III - REFERENCES TO OTHER CLASSES

SEE OR SEARCH CLASS:

4, Baths, Closets, Sinks, and Spittoons,   for valves combined with devices of that class, and for valves specialized for use in such devices.
16, Miscellaneous Hardware (e.g., Bushing, Carpet Fastener, Caster, Door Closer, Panel Hanger, Attachable or Adjunct Handle, Hinge, Window Sash Balance, etc.),   subclass 117 for insulated handles adapted for general use on rotary stems.
29, Metal Working,   subclasses 888.4+ and 890.12+ for processes of making valves and valve seats.
48, Gas: Heating and Illuminating,   subclass 58 for valves for acetylene generators.
49, Movable or Removable Closures,   appropriate subclasses for closures of the type provided for and see the search notes thereto in References to Other Classes for the loci of closures in other classes.
62, Refrigeration,   appropriate subclasses, for a refrigeration producer including an expansion valve specialized to such purpose, particularly subclasses 204+ , 210+, 216, and 528.
70, Locks,   subclasses 175+ and 242+ for lock mechanisms for valves where no particular structure of the valve beyond accommodation of the lock is involved.
73, Measuring and Testing,   subclasses 179 , 203, 220, 221, 249, 265+, 268+, 271, and 276 for valve organizations associated with major devices.
84, Music,   the various "pneumatic" and wind instruments, for valves specialized for such devices.
91, Motors: Expansible Chamber Type,   appropriate subclasses for valves combined with expansible chamber motors, the valve acting as a control for the motive fluid for the motor.
110, Furnaces,   appropriate subclasses, for valve organizations associated with furnaces.
114, Ships,   subclasses 197 and 198, for boat plugs and sea cocks.
116, Signals and Indicators,   subclasses 67+ for valves in combination with alarms, and subclass 277, for valve position indicators.
122, Liquid Heaters and Vaporizers,   subclasses 437 , 451.2, and 507 for valves associated with liquid heaters and vaporizers.
123, Internal-Combustion Engines,   subclasses 90.1+ and 188.1+ for valves peculiar to internal-combustion engines.
126, Stoves and Furnaces,   subclasses 285+ for dampers.
128, Surgery,   subclasses 207 , 210 and 211, for valved inhalers.
137, Fluid Handling,   for fluid handling apparatus and processes not otherwise provided for including combinations with valves, certain special types of valves with or without actuators, and valves with complex actuators; subclasses 38+ for valves operated by change of position or inertia of the system; subclasses 47+ for speed responsive valve control; subclasses 67+ for flow control by destructible or deformable means; subclasses 171+ for fluid separating valves in diverse fluid containing pressure systems; subclasses 233+ for valves for inflatable articles such as tires; subclasses 243+ for valve grinding motion of valves on seats; subclasses 246+ for lubrication or liquid supplied at the valve interface; subclasses 247+ for liquid valves and liquid trap seals; subclasses 269+ for valves convertible to change the mode of operation; subclasses 272+ for hydrant valves; subclasses 309+ for regenerative furnace type reversing valves; subclasses 329.1+ for repair check valves; subclasses 382+ for valve guards; subclasses 383+ for valves with locks or seals; subclasses 386+ especially subclasses 397, 398+ and 409+ for float controlled valves; subclasses 454.2+ for removable valve head and seat units, see the search notes thereto; subclasses 455+ for line condition change responsive valves, such as safety valves, pressure regulators and check valves; subclasses 544+ for valves with filters or strainers; subclasses 551+ for valves with indicators, registers, recorders, alarms or inspection means; subclass 560 for valves combined with other structure; subclasses 561+ for fluid handling systems including valves, particularly subclasses 615+ for valves actuated by swinging spouts and subclasses 625+ for multiway valve units; subclasses 624.11+ for a distribution system including a programmer or a timer.
138, Pipes and Tubular Conduits,   subclasses 40+ for similar structure where the flow is not cut off entirely, subclasses 89+ for nonvalve closures and plugs for conduits, especially subclasses 94.3+ for line blinds, and see (1) Note thereunder for the line.
141, Fluent Material Handling, With Receiver or Receiver Coacting Means,   appropriate subclasses for valved filling devices.
152, Resilient Tires and Wheels,   subclasses 415+ for inflating devices, for pneumatic tires.
166, Wells,   subclass 97.1 for a valve on a cap or wellhead, and subclasses 316+ for below-ground well devices with valves.
169, Fire Extinguishers,   subclasses 19+ for valves associated with sprinkler systems designed to extinguish fires.
177, Weighing Scales,   subclasses 60+ for weigher responsive flow control.
184, Lubrication,   for lubricating devices with valves, particularly subclasses 33 through 35for pump lubricators with valves, subclasses 66+ for gravity feed type lubricators with automatic valves and subclasses 80, 82, 83, 86, and 87 for other gravity feed lubricators with valves.
193, Conveyors, Chutes, Skids, Guides, and Ways,   subclasses 20 , 21, 28, 31+, 32, and 39 for devices controlling the flow of chutes.
200, Electricity: Circuit Makers and Breakers,   subclass 61.86 for valve operators, manipulation of which additionally makes or breaks a circuit, and subclasses 81.9+ for flow responsive devices which control elements of a switch.
202, Distillation: Apparatus,   subclasses 255+ for valves specialized to distillation.
209, Classifying, Separating, and Assorting Solids,   for valve combinations, particularly subclass 246 , for sifter feeding hoppers with cut-offs and valves, subclass 258, for discharging valves for sifters, and subclasses 488+, 490+ and 497+, for feeding and discharging means for stratifiers.
210, Liquid Purification or Separation,   appropriate subclasses for various combinations of a valve and separator, particularly subclasses 92 , 97+, 181, 245, 277+, 313, 340, 362, 392, 395+, and 418+.
215, Bottles and Jars,   subclasses 17+ for valved closures having features to prevent refilling of the receptacle and subclasses 311+ for other valved closures.
217, Wooden Receptacles,   subclasses 99+ for valved barrel bungs.
220, Receptacles,   subclasses 200+ for closures adapted to remain in the articles with which they are associated, and see the notes thereto for closures, and subclass 86.1 for milking pails with a valved inlet.
222, Dispensing,   for valves, cut-offs and discharge controllers in dispensing combinations, as where (a) the structural features of a supply container with or without material guiding means or the relation of the valve or its actuator thereto is claimed, (b) a dispensing type discharge assistant is claimed in combination with a valve, cut-off or discharge controller, (c) a preset or automatic cut-off is controlled by dispensed volume or rate of flow, (d) plural valves are so related as to have a measuring function, (e) or the valve, cut-off or discharge controller is considered to be specially adapted for dispensing purposes, as those operated by pressure applied to the contents of the supply container or by inversion of the supply container.
235, Registers,   subclass 94 , for devices for registering the number of times a valve is operated.
236, Automatic Temperature and Humidity Regulation,   for thermostatically-controlled valves.
239, Fluid Sprinkling, Spraying, and Diffusing,   subclasses 87 , 93+, 95, 96, 537+, and 569+ for valves in nozzles.
250, Radiant Energy,   subclasses 229+ for prephotocell light valves.
261, Gas and Liquid Contact Apparatus,   for valves associated with special contact apparatus.
303, Fluid-Pressure and Analogous Brake System,   subclasses 54+ for self-lapping valves and subclass 84.1+ for flow retarders and cut-offs.
359, Optics: Systems (Including Communication) and Elements,   subclasses 227+ and 238+ for light valves.
361, Electricity: Electrical Systems and Devices,   subclasses 254+ for gas-controlled valves operated by magnets, utilized in igniting means.
383, Flexible Bags,   subclasses 44+ for the combination of a bag with a valve-type closure.
401, Coating Implements With Material Supply,   appropriate subclasses, see particularly, subclasses 36 , 40+, 45+, 135, 136, 204, 205+, 219+, 232+, 258+, 263+, 270+.
406, Conveyors: Fluid Current,   subclasses 124+ for valves between plural receptacles in series at the conveyor inlet; and subclasses 127+ for valves between a conveyor and a material feeding receptacle.
454, Ventilation,   subclasses 265+ , 322+ and 333+ for valves associated with ventilating means.
604, Surgery,   subclasses 32 through 34, 236 to 238, 248 to 250 and 256.
D23, Environmental Heating and Cooling, Fluid Handling and Sanitary Equipment,   subclasses 200+ for fluid handling or treatment equipment and subclasses 233+ for valves.

SUBCLASSES

[List of Patents for class 251 subclass 1.1]    1.1BLOW-OUT PREVENTERS (I.E., COOPERATING SEGMENTS OF ANNULUS:
 This subclass is indented under the class definition.  Subject matter comprising a plurality of relatively movable flow obstructing members which control an annular flow passage about an axial rod or pipe as between a well casing and drill stem and have characteristics which go beyond a mere sealing means.

SEE OR SEARCH THIS CLASS, SUBCLASS:

146,for valves and/or couplings made in sections to facilitate mounting on continuous conduits.

SEE OR SEARCH CLASS:

166, Wells,   subclasses 75.11+ , especially subclasses 86.1+ and 88.1 for well heads comprising blow-out preventers and additional means for handling fluid from the well or other specific well features, and subclasses 179+ and the subclasses there noted for packers or plugs inserted into a prepositioned well conduit.
222, Dispensing,   subclasses 502+ for sectional valves in dispensers.
227, Elongated-Member-Driving Apparatus,   appropriate subclasses, for a packing between a casing head and an inner pipe or rod particularly subclass 4 for a pipe end attached packing assembly, subclasses 5+ for a packing between a casing head and a longitudinally moving coupled rod, and subclass 31 for a rotatable packing for an axially moving rod.
277, Seal for a Joint or Juncture,   for a generic sealing means or process, subclasses 324+ for a seal for well apparatus having an overpressure control device that may include extrusion preventing (i.e., anti-extrusion) structure.
285, Pipe Joints or Couplings,   subclass 123.14 for joints between concentric stationary pipes (e.g., and packing type blow-out preventer between a well casing head and a tubing).
  
[List of Patents for class 251 subclass 1.2]    1.2Deformable annulus:
 This subclass is indented under subclass 1.1.  Subject matter wherein one of the flow obstructing members comprises an annular member capable of having its shape changed by application of a force to thereby control flow through the annular flow passage.
  
[List of Patents for class 251 subclass 1.3]    1.3Radial reciprocating ram:
 This subclass is indented under subclass 1.  Subject matter .l which includes a member mounted for reciprocation in a radial direction to exert and relieve pressure on one of the flow obstructing members to open and close the annular flow passage.
  
[List of Patents for class 251 subclass 3]    3PATTERN TRACER CONTROLLED ACTUATOR:
 This subclass is indented under the class definition.  Subject matter wherein the valve is provided with an actuator including a tracer element which is designed to contact a pattern.
(1) Note. This type of actuation is usually used in duplicating machines wherein the pattern is the shape of the article to be made and the valve is the control subcombination of the duplicating machine.

SEE OR SEARCH CLASS:

91, Motors: Expansible Chamber Type,   subclass 37 for expansible chamber motors controlled by a pattern or template controlled valve.
409, Gear Cutting, Milling, or Planing,   subclasses 79+ for a pattern controlled milling machine.
  
[List of Patents for class 251 subclass 4]    4TUBE COMPRESSORS:
 This subclass is indented under the class definition.  Devices which control flow by compression of a flexible fluid conveying tube.

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24, Buckles, Buttons, Clasps,   etc., subclasses 129+ to 136+ for similar structures for clamping or holding cords or ropes, and subclasses 243+ for clasps of general utility.
81, Tools,   subclasses 300+ for pliers and subclasses 53+ for wrenches.
137, Fluid Handling,   subclasses 355.18+ for tube compressors combined with hose storage or retrieval means.
  
[List of Patents for class 251 subclass 5]    5Fluid pressure actuated:
 This subclass is indented under subclass 4.  Devices which are actuated by fluid pressure.
  
[List of Patents for class 251 subclass 6]    6Roller tube contacting element:
 This subclass is indented under subclass 4.  Devices comprising rollers which contact and compress the conveyor.
  
[List of Patents for class 251 subclass 7]    7Perpendicularly reciprocating tube contacting element:
 This subclass is indented under subclass 4.  Devices comprising a tube contacting portion which reciprocates perpendicularly of the axis of the flexible conveyor.
  
[List of Patents for class 251 subclass 8]    8Screw actuated:
 This subclass is indented under subclass 7.  Devices having screw means to actuate the contacting portion.
  
[List of Patents for class 251 subclass 9]    9Pivoting tube contacting element:
 This subclass is indented under subclass 4.  Devices comprising a tube contacting portion which pivots, as a lever, to compress the conveyor.
  
[List of Patents for class 251 subclass 10]    10U-shaped resilient bar or rod:
 This subclass is indented under subclass 9.  Devices comprising a U-shaped resilient bar or rod which pivots at its base to cause the leg portions to grasp the tube.
  
[List of Patents for class 251 subclass 11]    11HEAT OR BUOYANCY MOTOR ACTUATED:
 This subclass is indented under the class definition.  Subject matter wherein the valve is provided with a device which converts heat energy into motive power or in which energy from a variation in buoyancy of a body is used to actuate the valve.
(1) Note. An example of a buoyancy motor is a hollow shell which when full of liquid sinks in the liquid but which floats when the liquid is pumped out of the shell.

SEE OR SEARCH CLASS:

60, Power Plants,   subclasses 495+ for motors having a buoyant working member motivated by the vertical rise and fall of the surface of a body of fluid, and subclasses 508+ or 516+ for motors which transduce temperature variation to work through the expansion or contraction of a confined solid, liquid or gas.
137, Fluid Handling,   subclass 76 for heating means for heat destructible or fusible control elements, subclasses 334+ for means for supplying or exchanging heat in fluid handling means, especially subclass 341 for electric heating elements and see the search notes to subclass 334, subclasses 386+, and the subclasses mentioned in the notes thereto, especially subclass 404 for sinking or bucket type floats and subclass 409, for float actuated, liquid level responsive valves, and see the search notes to subclass 404 and subclass 468 for temperature responsive means controlling valves, and see the search notes thereto.
  
[List of Patents for class 251 subclass 12]    12FLUID ACTUATED OR RETARDED:
 This subclass is indented under the class definition.  Subject matter in which the opening or closing movement of the valve is produced or modified by the reactive force of a fluid acting against a portion of the actuating means.
(1) Note. All fluid displacement devices inherently require a period of time to fill or empty the same, the period depending upon the relative sizes of the displacement devices and the flow passages thereto as well as the pressures producing the flow. As a result, many of the disclosures of this and indented subclasses disclose and make use of this time delay, such as in the case of the "flush" valves, but other disclosures having equivalent constructions make no reference to such time delay. The definitions of this and indented subclasses have been drawn with a view to bring together inherently related disclosures irrespective of the mode of describing the function of the device.

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73,for biased trip valves with fluid pressure actuation of the trip.

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92, Expansible Chamber Devices,   appropriate subclasses for an expansible chamber device, per se.
123, Internal-Combustion Engines,   subclasses 90.12 through 90.14, for poppet valve operating mechanism which is fluid actuated.
137, Fluid Handling,   subclass 12 for a process of controlling flow by fluid pressure, subclass 14 for a process involving pressure control, subclass 15.18 for a process of assembling, disassembling, or repairing a fluid actuated or retarded valve, subclass 58 for a centrifugal mass type (i.e., exclusive of liquid) speed responsive valve control having a fluid servomotor, subclass 81.1 for an atmospheric pressure responsive control, subclasses 82-86 for pressure modulating relay or follower, subclass 105 for a supply and exhaust type self-proportioning or correlating vacuum suction pulsator type system (e.g., milking machine, etc.) using a pulsation responsive pilot valve, subclasses 219-222 for Laner-Johnson valves, especially subclasses 221-222 for those having an internal servomotor with an internal pilot valve, subclasses 413-415 for fluid pressure type servo relay control of or response to liquid level and subclasses 455-543.23 for valves responding to change in line pressure and/or flow conditions to control the flow, especially subclasses 488-492.5 for fluid pressure type servomotor control of the valve, subclasses 596.14-596.16 for pilot actuated supply and exhaust valves, subclass 596.18 for a fluid motor actuated supply and exhaust valves, subclass 601.13 for systems dividing into parallel flow lines then recombining having a fluid actuated or retarded valve, subclass 625.6 for pilot actuated supply and exhaust multi way valve units, or subclass 625.66 for fluid motor actuated supply and exhaust multi way valve unit.
222, Dispensing,   subclasses 59+ for dispensers having flow meter operated cut-offs, subclass 334 for fluid motor operated discharge assistants in dispensers and subclass 504 for motor operated dispenser outlet elements.
  
[List of Patents for class 251 subclass 14]    14Fluid and non-fluid actuators:
 This subclass is indented under subclass 12.  Subject matter in which both a fluid actuator and an actuator other than one utilizing fluid are provided for alternative use.
(1) Note. Actuators which include both fluid actuation mechanism and non­fluid actuation mechanism but in which said mechanisms are not of themselves each capable of fully controlling the valve are not considered to be alternative within the scope of this subclass and are classified in an appropriate subclass for the fluid actuation mechanism and cross referenced for novel nonfluid actuation mechanism. Examples of such excluded devices are electrically controlled pilot valves in subclass 30 and manually opened and fluid pressure closed valves in subclasses 48+.

SEE OR SEARCH THIS CLASS, SUBCLASS:

30,for electrically controlled fluid actuators, and see (1) Note.
48+,for manually opened, fluid pressure closed valves and see (1) note.
130,for electrical actuators combined with a nonfluid, nonelectrical actuator.
  
[List of Patents for class 251 subclass 15]    15Compulsory cut-off after flow period:
 This subclass is indented under subclass 12.  Subject matter in which the flow of fluid, when established by external means under the control of the operator, is stopped after an interval of time irrespective of the continued application by the operator of the original control effect that initiated the flow.

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48+,for fluid actuated devices which delay closing but are not effective until the external control is released.

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137, Fluid Handling,   subclasses 386+ for control by liquid level responsive means, i.e., by accumulated quantities in a container or a control chamber which reflects the condition in the container and subclasses 456+ for safety cut-offs which require manual resetting.
222, Dispensing,   subclasses 14+ for dispenser cut-offs operated by selectively preset volume or rate of flow responsive mechanism, and subclasses 59+ for dispenser cut-offs operated by rate of flow responsive mechanism.
  
[List of Patents for class 251 subclass 16]    16Serial main line cut-off and manual valves (e.g., hydraulic "fuses"):
 This subclass is indented under subclass 15.  Subject matter in which a manually controlled valve and a fluid actuated or retarded shut-off valve are sequentially arranged in the flow line so that flow takes place only during the time both valves are open.
(1) Note. The shut-off valve is usually a safety or loss preventing valve intended to prevent prolonged use of the fluid under external control or loss in case of rupture of a hydraulic line. They are frequently called hydraulic fuses.
(2) Note. Since these valves are reset only by operation of the manual valve they are included here even if claimed as a subcombination.

SEE OR SEARCH CLASS:

137, Fluid Handling,   subclasses 102+ for devices, sometimes called "hydraulic fuses", in which flow between a pump and distributor valve is interrupted after an interval unless exhaust flow from the distributor valve to the reservoir occurs; subclass 467 for valves which open in response to a change in line condition and require resetting, and subclasses 613+ for distributing systems comprising a single flow path with plural serial valves and/or closures.
  
[List of Patents for class 251 subclass 17]    17Interconnected motion:
 This subclass is indented under subclass 16.  Subject matter in which the manual and fluid actuated or retarded valve are conjointly actuated at least during a portion of their motions.
(1) Note. In some disclosures in this subclass, one valve is manual only and one is opened manually and closed or retarded by fluid pressure means, and the first valve prevents flow during the manual opening of the second or fluid actuated valve and opens only when the fluid actuated or retarded valve has started its closing motion.
  
[List of Patents for class 251 subclass 18]    18Manual and pilot valves:
 This subclass is indented under subclass 17.  Subject matter in which the fluid actuated or retarded valve is controlled by a pilot valve that is interconnected with and moved by the manual valve.

SEE OR SEARCH THIS CLASS, SUBCLASS:

25+,for fluid servo-motor actuated valves, and see the search notes to subclass 25.
  
[List of Patents for class 251 subclass 19]    19Auxiliary pilot valve overrides a first pilot valve:
 This subclass is indented under subclass 15.  Subject matter in which the main valve is opened by adjustment of a control or pilot valve in a servo actuating system for the main valve but is caused to start closing by a second control or pilot valve made effective by the opening of the main valve, irrespective of the adjustment of the first pilot valve.

SEE OR SEARCH THIS CLASS, SUBCLASS:

29,for fluid actuated pilot valves with additional pilot valve control.
  
[List of Patents for class 251 subclass 20]    20Forced return of actuator to cut-off position:
 This subclass is indented under subclass 15.  Subject matter in which the actuator which opens the valve is subjected to an overriding closing force by a fluid actuated or retarded device only after the completion of the desired flow period.

SEE OR SEARCH CLASS:

222, Dispensing,   subclasses 17+ for preset volume dispensers in which a moving cut-off operating element returns to its neutral setting during dispensing.
  
[List of Patents for class 251 subclass 21]    21Actuator connection released on opening of cut-off valve:
 This subclass is indented under subclass 15.  Subject matter in which coacting elements of the external actuating means for the valve are so related to each other that they transmit an opening motion to the valve, but upon the valve attaining its open position the co-acting elements are sufficiently disengaged as to permit the valve reclosing under the action of the fluid actuating or retarding means even if the opening force on the external means is maintained.
  
[List of Patents for class 251 subclass 22]    22Control fluid released into closed build-up chamber:
 This subclass is indented under subclass 15.  Subject matter in which a control pressure normally maintaining the valve closed is momentarily reduced, so that the valve can open, by discharge into an empty closed chamber, but upon the subsequent rise in pressure, due to filling of the chamber, the valve recloses.

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33+,for choked pressure fluid type servo-motors in which the discharge of the fluid in the choke chamber is to waste or to the line, the flow being terminated by reverse movement of the pilot valve.
  
[List of Patents for class 251 subclass 23]    23Dashpot interconnects actuator and valve:
 This subclass is indented under subclass 15.  Subject matter in which a valve biased toward its closed position is opened by a force transmitted through a trapped body of fluid in a chamber having a restricted inflow or outflow opening and recloses under its bias when sufficient flow through the restricted opening has taken place.

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57,for fluid link or column actuators for valves.
  
[List of Patents for class 251 subclass 24]    24Venturi or line flow effect assisted:
 This subclass is indented under subclass 12.  Subject matter in which the valve has the opening or closing forces acting thereon augmented or altered by a force resulting from a fluid pressure derived from the velocity flow of fluid in the line acting on a reactor surface other than the valve head or closure element.

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37,for choked fluid pressure type servo-motors having a choke or restriction in the main line.
123+,for valves located at a point of restriction in a line.

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137, Fluid Handling,   subclasses 219+ for Larner-Johnson valves, in which the needle seats on a restricted portion of the flow line and subclasses 497+ for valves having a separate connected fluid reactor surface and adjusted entirely by variations in fluid flow in the line, especially subclass 502 for expansible chamber reactors subject to differential pressures, one pressure being that at the throat of a Venturi tube.
  
[List of Patents for class 251 subclass 25]    25Pilot or servo type motor:
 This subclass is indented under subclass 12.  Subject matter in which the valve is actuated, at least in part, by a fluid pressure motive means deriving its power from either the fluid line or a separate source of fluid pressure and controlled by an auxiliary or pilot valve or valves.
(1) Note. Fluid pressure servo-motors having valves both for the inlet and the outlet or vent of the pressure chamber are in this subclass.

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91, Motors: Expansible Chamber Type,   appropriate subclasses for expansible chamber motors, per se.
137, Fluid Handling,   subclass 46 for inertia responsive systems having servo mechanisms, subclass 58 for centrifugal governor controlled servo actuated valves, subclasses 82+ for pressure modulating relays or followers, subclass 105 for pulsators with pulsation responsive pilot valve, subclasses 191 and 195 for gas and liquid separating traps having servo-control of the valves, subclasses 219+, especially subclass 222 for Larner-Johnson type valves having hollow telescoping sections which function as servo units, subclasses 413+ for fluid pressure servo-motor operation of a level responsive valve, subclasses 485+ for servo-operated line condition responsive valves, and subclasses 596.14+ for pilot actuated supply and exhaust valves, and subclasses 625.6+ for pilot actuated supply and exhaust multiway valve units.
  
[List of Patents for class 251 subclass 26]    26Alternative pressure sources or pilot valve:
 This subclass is indented under subclass 25.  Subject matter in which the servo-motor may receive fluid from any one of two or more sources of fluid pressure or in which two or more pilot valves are employed for a single servo unit, one pilot valve duplicating the function of another pilot valve.

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19,for servo-systems having an additional pilot valve which compels reclosing of the main valve irrespective of the position of the first pilot valve.
25+,for servo-systems in which there are two or more pilot valves not duplicative of their functions and not classifiable in subclasses 29 and 31, such as inlet and outlet valves.
29,for pilot valves controlling fluid flow to a fluid actuated pilot valve.
31,for servo-systems in which a plurality of pilot valves control a corresponding number of servo units.

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137, Fluid Handling,   subclasses 65+ for plural servo-motor control valves in a speed responsive prime mover control.
  
[List of Patents for class 251 subclass 27]    27Servo failure responsive control of main valve:
 This subclass is indented under subclass 25.  Subject matter in which means are provided for causing the main valve to assume a position other than biased open or biased closed upon a loss of servo operating pressure, i.e., a position other than that which the uncontrolled valve would assume under pressure of the material flowing through the line.
  
[List of Patents for class 251 subclass 28]    28Fluid actuated pilot valve:
 This subclass is indented under subclass 25.  Subject matter in which the auxiliary or pilot valve controlling the main valve is operated by a fluid responsive device.

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32,for latched pilot valves for fluid servo-motors with fluid pressure means to release the latch.

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137, Fluid Handling,   subclass 105 for such systems in which the pilot valve is itself controlled by the main valve. These are generally suction operated milker pulsators and subclasses 485+ for line condition change responsive valves having fluid actuated pilot valve means which responds to changing pressures or flow conditions in the line.
  
[List of Patents for class 251 subclass 29]    29With additional pilot valve control:
 This subclass is indented under subclass 28.  Subject matter in which the fluid responsive device that operates the pilot valve is controlled by an additional pilot valve.

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26,for plural alternative pilot valves, and see the search notes on plural pilot valves in the definition.
  
[List of Patents for class 251 subclass 30.01]    30.01Electrically actuated pilot valve:
 This subclass is indented under subclass 25.  Subject matter in which the auxiliary or pilot valve controlling the valve is operated by electrical energy.

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32,for electrically released trip pilot valves.
129.01+,for electrical actuators for main valves, and see the search notes to subclass 129.

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137, Fluid Handling,   subclass 315.03 for a fluid handling system with repair, tapping, or assembly means for an electromagnetically actuated valve (e.g., solenoid, etc.), subclass 596.16 for systems having an electrically actuated pilot valve for a supply and exhaust valve, subclass 599.07 for systems having separately actuated valves operated in common by an electrically actuated digital flow controller and their flow lines, subclass 601.14 for systems dividing into parallel flow lines then recombining having an electrical valve actuator, or subclass 625.64 for system shaving an electrically actuated pilot valve for a supply and exhaust multi way valve unit.
  
[List of Patents for class 251 subclass 30.02]    30.02Main valve biased closed by fluid pressure:
 This subclass is indented under subclass 30.01.  Subject matter in which force per unit area exerted by a fluent material is used to maintain the valve in a position which closes a passage to fluid flow until the valve actuator moves for valve to a position which opens the passage.
  
[List of Patents for class 251 subclass 30.03]    30.03Venting passage within movable main valve:
 This subclass is indented under subclass 30.02.  Subject matter in which the valve is opened by releasing pressure through a passageway in a movable portion of the valve.
  
[List of Patents for class 251 subclass 30.04]    30.04Pilot valve movably mounted within or around main valve:
 This subclass is indented under subclass 30.03.  Subject matter in which movement of the pilot valve is limited by the movable portion of the main valve, the pilot valve being either contained or guided by the movable portion of the main valve.
  
[List of Patents for class 251 subclass 30.05]    30.05Fluid pressure sole means for biasing valve closed:
 This subclass is indented under subclass 30.02.  Subject matter in which the force per unit area exerted by a fluent material is the only agent used to maintain the main valve in the position.
  
[List of Patents for class 251 subclass 31]    31Double or oppositely acting motor units:
 This subclass is indented under subclass 25.  Subject matter in which the main valve is operated in one direction by a servo unit and another direction by a second servo unit.
(1) Note. The oppositely acting servo units of this subclass may constitute different sides of the same piston and further the pilot controls for the opposing servo units may be utilized, as in a single reversing or four-way valve.

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91, Motors: Expansible Chamber Type,   appropriate subclasses for servo-motors, per se.
137, Fluid Handling,   subclass 596.15 for supply and exhaust valves operated by plural servo-motors controlled by a single pilot valve, and subclass 625.63 for supply and exhaust multiway valve units operated by plural servo-motors controlled by a single pilot valve.
  
[List of Patents for class 251 subclass 32]    32Latched pilot valve:
 This subclass is indented under subclass 25.  Subject matter in which the pilot valve is engaged in one position by a detent which retains the pilot valve in that position until released by the detent.

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66+,for biased trip valves, especially subclass 73 for fluid pressure trip actuation.
89+,for valve actuators associated with means for blocking or disabling the actuator.
  
[List of Patents for class 251 subclass 33]    33Choked pressure type servo motor:
 This subclass is indented under subclass 25.  Subject matter in which the servo-motor is of the type having an expansible pressure chamber the pressure in which is equalized with either a high or a low pressure region by means of a constantly open but restricted passage or communication therebetween to cause the main valve to assume one position, but in which the pressure conditions can be reversed by the opening of a pilot valve in an open or less restricted passage between the chamber and a pressure region other than that connected by the restricted passage to cause the main valve to assume an opposite position.
(1) Note. Expansible chamber devices which are constantly open to a single pressure region, even though the opening is restricted, are not servo-motors because motor action can result only by receiving fluid at a higher pressure and exhausting to a lower pressure. Such devices are either a form of fluid bias or a dashpot or other vented chamber.

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50+,for dashpot of fluid controlled retarders or timers receiving pressure from the line controlled. See (1) Note.

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