This class is limited to motors for converting the energy of
a pressure fluid into mechanical work in which a charge of simple pressure fluid is admitted to an expansible chamber, the expansion of said chamber converting into work only the original energy of the charge, the charge after expansion of said chamber being exhausted to some place other than whence it came, and in which no energy is extracted from the charge except by expansion of the chamber, said motors when of the reciprocating or oscillating type including control of the fluid.
(1) Note. Claims Not Controlling in Patents Prior to 1936. Patents issued prior to 1936 have not necessarily been classified by claims so that the placement of these patents does not necessarily indicate lines of classification. However, most of the patents regardless of their age have been placed in accordance with their claimed subject matter.
PLACEMENT OF PATENTS
A. Involving Combination and Subcombination Subclasses:
In many instances the schedule of this class provides for a combination which requires a given subcombination, and elsewhere below provides for the subcombination.
The following rule has been followed as to the placement of the original patent, and as to cross-referencing, and should be followed in the future.
Where the combination subclass requires the same subcombination as is provided for in the subcombination subclass (i.e., subcombination defined with the same specificity in both subclasses) a patent disclosing the combination is placed as an original in, or under, the combination subclass regardless of whether the claims are directed to the combination or subcombination and is not cross-referenced to the subcombination subclass. A patent disclosing only the subcombination and claiming same is placed as an original in the subcombination subclass and is not cross-referenced to the combination subclass.
This rule is applicable only in instances where there is but a single subcombination subclass (i.e., no indented subclasses), but the combination subclass may be further subdivided into indented subclasses. The prime feature of this situation is that the subcombination must, by definition, be of equal specificity in the two subclasses. A search for the subcombination, at least in the case where it is adapted to be used in the combination, of necessity involves all of the patents in the combination subclass. Under this system of placing the patents a complete search of the combination can be made in the combination subclass, and of the subcombination in both subclasses without the addition to the search files of the otherwise necessary cross-reference copies.
The subclasses involved in this combination-subcombination relationship have been indicated in the schedule by numbers in parenthesis, as explained in a paragraph after the class title.
Exemplary of this situation in the indented subclasses (223-229) provide for a distributor (valve) in the piston of a cyclically operable motor combination while subclass 422 requires only a valved piston subcombination. As between these subclasses any patent having a disclosed cyclically operable motor is placed as an original in subclass 222 or one of the indented subclasses regardless of whether the means which makes the motor cyclically operable is claimed and is not cross-referenced in subclass 422. A complete search for the subject matter provided for in subclass 422 of necessity involves all of the patents in subclasses 222+.
B. Involving Ancillary or Auxiliary Expansible Chamber Motor:
In many instances the claimed motor which provides the basis of classification for a patent in Class 91 is provided with another expansible chamber motor which merely performs an ancillary or auxiliary function for the main motor. Illustrative of such functions are motor valve or lock, or lubricator actuation. In such cases the structure or operation of the ancillary motor does not constitute a basis for original classification of the patent in the Class 91 schedule unless the patent includes a claim to the auxiliary motor, per se. However, the patent may be cross-referenced on the basis of the auxiliary motor. For example, see subclasses 6+ and 282+. Subclasses 6+ provide for fluid supply through diverse paths to a single expansible chamber. In this case the chamber must be a chamber of the motor which causes the patent to be classified in Class 91. Subclasses 282+ provide for the same type of supply to a motor chamber, but in this case the motor is an auxiliary motor in that it actuates the distributor of another motor. This type of control of a distributor motor does not cause classification of the patent as an original in subclasses 6+, but cross-reference to subclasses 6+ is appropriate.
LINES WITH OTHER CLASSES
Combinations With Load Devices.
Inasmuch as the basic purpose of a motor is to operate a load the inclusion of the load in the claim by name only or in general terms will not exclude a patent from this class. An exception to this general rule exists where the load on the motor is a valve. The combination of an expansible chamber motor and a valve as the load driven thereby, even if the valve is claimed by name only, is excluded from this class and will be found in Class 137, Fluid Handling, or Class 251, Valves and Valve Actuation. A second exception exists where the claimed nominal load on the motor is an expansible chamber means solely disclosed as the master of a pulsator.
This combination is classifiable in Class 60, subclasses 533+.
This line also applies where the load is a tool; that is, a named tool driven by the motor will not exclude a patent from this class if no tool details are recited. However, if a support for the work being acted upon by the tool is claimed, classification in the appropriate tool class results even though both the tool and the support are claimed by name only. Also see the Search Class 173 note in section III below for the line with regard to a nominally claimed tool driven by an expansible chamber motor combined with other features such as work cleansing or tool feeding.
No attempt has been made to review the classification of all patents found in classes relating to loads adapted to be driven by a motor. Thus, it is to be noted that the original classification of all patents is not consistent with the above statement as to nominally claimed loads and this particularly applies as to classes not recently reclassified. In those instances in which a body of art is known to exist in a given class, in which the load on the motor is claimed only nominally, and especially where the classification of that class provides for a fluid motor actuator for the device, currently issuing patents will not be classified as originals in Class 91 even though the load is only nominally claimed. The means which transmits power from the working member of the motor to the load to be driven (e.g., linkage, gearing, etc.) is not considered to be the load for the motor. See the Search Class 74 note in the class definition of Class 91 for a further discussion of this subject.
RELATIONSHIP TO CLASS 92
Class 92 is directed to expansible chamber devices, per se, and is related to Class 91 as a subcombination thereof. Class 92 is limited to expansible chamber devices in which the working member has an oscillating or reciprocating motion to expand and contract the expansible chamber. Thus, Class 92 cannot take the subcombination of any Class 91 motor in which the working member is of the rotating type as defined in subclass 58 of Class 91.
With respect to expansible chamber motors in which the working member has a reciprocating or oscillating motion to expand and contract the expansible chamber, Class 92 will take those patents in which no control of the motive fluid by a valving action is claimed. Thus, any claimed valving of motive fluid of an expansible chamber motor in sufficient to preclude classification is Class 92 even though the valving claimed may not be all of the valving necessary to cause the motor to operate in the intended manner. However, if a claim is for an expansible chamber motor driving a specifically claimed Class 92 device, then classification is in Class 92 regardless of the details of the expansible chamber motor
recited.
See Class 92, subclasses 3+. For the classification of various subcombination features of Class 92 devices elsewhere classified see the class definition and appropriate notes in Class 92.
With regard to claim interpretation to determine whether valving is claimed to cause classification in Class 91, or is not claimed thus permitting classification in Class 92 the following criteria have been followed:
1. Claims which include a limitation such as "means for supplying fluid to the motor" or "means supplying fluid to the motor" are construed as requiring no more than the conduits or ports which supply the fluid and would, therefore, not be interpreted as including valving for Class 91.
2. Claims which include a limitation similar to that in (1) above, but with a further limitation which indicates a change in supply of working fluid such as--alternately, periodically, intermittently, pulsing, fluctuating, reversing flow, etc.--are construed as necessarily including more than a mere conduit or port and are excluded from Class 92. These patents would thus be classified on their claimed disclosure of what performs the noted change in the supply. Thus, a patent claiming "means (for) alternately supplying motive fluid to the motor" would be classified in Class 91 if said means is disclosed as a valve.
3. A port in an expansible chamber wall which is disclosed as controlled by the working member as, for example, an exhaust port which is overrun by a piston, together with the working member constitutes valving for Class 91. If such a port is claimed classification is in Class 91 regardless of whether the claim sets forth that the working member controls the port.
RELATIONSHIP TO CLASS 60
The general line between Class 91 and Class 60 is that if subject matter relating to power production comprising more than an expansible chamber motor or more than a plurality of such motors is claimed, classification is in Class 60 if otherwise appropriate. More specifically the line may be categorized as follows:
A. Plural or combined type motors
(1) The combination of a motor classifiable, per se, in Class 91 with a motor of another type (including a pulsator) i.e., one which, per se, would be classified in another motor class, is classified in Class 60. See Class 60 subclasses 698+.
However, the combination of a Class 91 type motor with a second motor which performs an ancillary function only of the Class 91 type motor (e.g., valve operating motor) and provides no power for external use is not excluded from Class 91 even if the second motor is of another type (e.g., electric motor).
(2) The combination of a plurality of Class 91 type motors or a Class 91 type motor having a plurality of working members (e.g., pistons) is classified in Class 91. See the Search Class 60 note in subclass 170 of Class 91 for a further statement of this line.
B. Motive fluid source, modification or exhaust treatment
(1) Pumps.
The inclusion in a claim of a pump broadly which provides motive fluid for utilization by the Class 91 motor does not preclude classification in Class 91.
The following examples of terminology have been considered to be nominal inclusion of a pump and if so claimed would not preclude classification in Class 91: (a) a pump; (b) a rotary pump; (c) a motor driven pump; (d) a motor driven rotary pump; (e) an internal combustion engine having an intake manifold (as a source of vacuum); (f) a plurality of pumps arranged in parallel; (g) a circuit comprising a sump, pump and motor.
The following examples have been considered to be significant inclusion of a pump, and if so claimed would preclude classification in Class 91 and cause classification in Class 60, if otherwise appropriate: (a) a pump which is characterized as to type, e.g., centrifugal, eduction, constant displacement, variable displacement, pulsator, etc., (however, see (b) in the preceding paragraph); (b) a motor driven pump in which the motor is characterized as to type, e.g., turbine, electric motor, internal combustion engine (however, see (e) in the preceding paragraph); (c) a pump which has any detail thereof recited as, for example, a "piston"; (d) a plurality of pumps in series; (e) a particular physical relation between a nominal pump, and (1) a motor supplied thereby, or (2) with a sump, reservoir or tank forming part of the circuit supplying the pump. For example, this particular physical relation may include their relation in space or mechanical interconnection means.
See particularly Class 60 subclasses 325+. (2) Accumulators.
A motor having an expansible chamber in constant communication with an accumulator for pressurized motive fluid is not precluded from Class 91 regardless of the specificity with which the accumulator is recited, the accumulator in this case being considered to be merely a part
of the expansible chamber.
Class 60 takes an accumulator combined with a Class 91 motor in which a control valve means is interposed between the accumulator and expansible chamber unless the accumulator is claimed so broadly as to amount to a mere conduit. See particularly Class 60, subclasses 325+.
(3) Internal Generation.
Class 60 takes those expansible chamber motors in which the motive fluid within an expansible chamber is heated or cooled, as, for example, by a fluid in heat exchange relation with the interior of the chamber. Such a fluid may be the same motive fluid used in the chamber either before or after it passes through the chamber. See Class 60, subclass 508.
(4) Heating, Superheating or External Generation.
An expansible chamber motor having nominally claimed means to heat or superheat the motive fluid before introduction into the expansible chamber is not precluded from Class 91. For example, Class 91 takes a "boiler" combined with an expansible chamber motor while a "fire tube boiler" combined with a Class 91 motor would be classified in Class 60. See, for example, Class 60, subclasses 643+.
Class 91 does not take the combination of an expansible chamber motor with an explosive generation of motive fluid even if nominally claimed. See, for example, Class 60, subclasses 632+.
(5) Exhaust Treatment or Handling.
Class 60 takes combinations involving treatment of motive fluid after it leaves an expansible chamber where means is claimed to change some characteristic of the fluid. A condenser is an example of such a means, but the inclusion of a condenser in a claim by name only is not sufficient to preclude a patent from Class 91.
Class 60 also takes combinations involving handling of exhaust fluid from a fluid motor. This fluid is considered to be exhaust fluid for Class 60 after it leaves the last claimed valve means which could affect operation of the Class 91 motor. Handling is considered to necessarily include more than a mere pipe or chamber to conduct the exhaust fluid away. A valve for controlling a Class 91 motor, located in the exhaust line from the motor, designed to direct exhaust fluid to one or more of a number of exhaust passages is not exhaust fluid handling for Class 60. However, an exhaust fluid conductor having a number of ports therein merely for the purpose of dividing the exhaust stream is more than a mere chamber or pipe and is classified in Class 60. Claimed limitations to an elbow, support or other fitting which constitutes a mere part of the exhaust pipe will be ignored, but any significant relation of the pipe and motor will result in classification in the appropriate exhaust treatment subclass of Class 60. A particular physical relation or mechanical interconnection between a chamber or reservoir for receiving exhaust fluid from the motor and the motor has been considered exhaust handling for Class 60.
C. Pulsators
Class 60 takes pulsator systems in which a generally constant mass of confined motive fluid passes between pump and motor expansible chambers and returns to the pump by the same route or conduit. Class 60 also provides for such pulsator systems where additional fluid is added to the system whether the fluid is make-up fluid to replace leakage or pressurized motive fluid to operate the motor, unless the pressurized motive fluid is valved by a movable valve element which is mechanically connected to the pump working member so that movement of the working member will cause movement of the valve element. The latter combination is classified in Class 91. See the Search Class 60 note in subclass 6 of Class 91 for a further statement of this line.
It is to be noted that some pulsator systems which involve a generally constant mass of confined motive fluid include a valve such as a throttle between the pump and motor. The claiming of the motor and valve only in such a disclosed system is excluded from Class 91 in that the fluid does not exhaust to some place other than whence it came.
Search Class 60 subclasses 533+ for pulsators and pulsator systems.
RELATIONSHIP TO CLASS 418
Class 418, Rotary Expansible Chamber Devices, takes rotary expansible chamber motors even though the disclosure and claims may be restricted to motor use. In some ways Class 418 may be considered to be less comprehensive than Class 91, and rotary expansible chamber type motors in certain combinations enumerated below will be classified in Class 91 rather than Class 418. Unless specifically excluded below a patent to a rotary expansible chamber type motor as defined in the class definition of Class 418 will be classified as an original in Class 418 as opposed to Class 91.
(1) Valving
(a) Cyclic or Position Responsive: Class 418 will take rotary expansible motors combined with valves for the motive fluid which have a repetitive pattern or cycle of operation which is related to the rotation of the motor. These may be termed cyclic or position responsive valving and include the opening and closing of inlet or exhaust ports by the movement of this type valving so as to provide, for example, early cutoff of supply is also included in Class 418. The inclusion, however, of means to cutoff operation of the motor after a partial, full or predetermined number revolutions is excluded from
Class 418 and would cause classification in this class (91). See for example, subclass 2.
(b) In-line: An in-line valve is defined as one situated in the normal line of motive fluid flow which acts in some way to control the flow in the line, but not by diverting the fluid to a second or subsidiary flow line (e.g., waste). Class 418 will take all in-line valves combined with a rotary expansible chamber motor which are controlled by some means other than a condition of the motive fluid (e.g., manual throttle) and will also take those which are actuated directly by the application of the motive fluid thereto (i.e., direct response valves). Those devices including in-line valves which are controlled by a motive fluid condition (e.g., pressure, flow) and in which said valves are not of the direct response type are excluded from Class 418 and will be classified in Class 91 if otherwise appropriate.
(c) Branched Flow or By-pass: (1) Separate Valve Means: Those rotary expansible chamber devices which include a separate valve means (as opposed to a movable chamber part as discussed in paragraph (2) immediately below) to divert or by-pass all or a portion of the motive fluid from its normal or first course of flow to a second or waste path are excluded from Class 418 regardless of whether the valve is manually or otherwise controlled unless the diverted fluid is used merely for a motor perfecting function such as lubricating, cooling, vane bias, etc.
(2) Movable Chamber Part: Many rotary expansible chamber motors have expansible chamber parts which are in running contact with other chamber parts and which move from a "normal" or contacting position to a noncontacting position and in so moving allow passage or by-pass of motive fluid thereby. Examples of such parts are vanes, abutments, end plates, etc., and such parts are usually biased into contacting position by means such as a spring, pressure fluid conducted from the expansible chamber or the like. Such devices are not excluded from Class 418 even though the yielding of the part may be considered to be performing a by-pass function. However, if motive fluid is conducted to the part for such a biasing function (e.g., behind end plate) and there is a controlled application of fluid to or release of the fluid from the bias area for the disclosed purpose of by-passing said fluid or conducting it to another point of disposal such devices are excluded from Class 418 and are classified in Class 91 if otherwise appropriate.
(3) With Diverse Motor: The combination of a rotary expansible chamber motor with another motor of a different type (e.g., reciprocating, etc.), is excluded from Class 418. Unless the diverse motor is a mere auxiliary of the rotary expansible chamber motor, as for example, a valve actuating motor. See Class 91, subclass 61 for a combined rotary expansible chamber motor and a reciprocating motor. See Class
60, Power Plants, subclasses 698+, for other diverse motors one of which may be of the rotary expansible chamber type.
The Search Class notes below also include statements of the line with other classes.
REFERENCES TO OTHER CLASSES
SEE OR SEARCH CLASS
60, Power Plants, see (4) Note above for the relationship of Class 91 and Class 60.
73, Measuring and Testing,
232+, for expansible chamber type volume or rate of flow meters. Class 73 includes expansible chamber meters combined with registering mechanism and meters incapable of general use as an expansible chamber motor. A meter is considered to be incapable of such general use if there is not disclosed means to take power therefrom for external use such as to a registering mechanism. Therefore, Class 91 takes an expansible chamber device disclosed as a meter having means to take power therefrom such as for an unclaimed registering mechanism.
74, Machine Element or Mechanism, appropriate subclasses for machine elements and mechanisms, per se, and in combination with a nominally claimed expansible chamber motor. In general gearing or linkage included as part of the power output means from an expansible chamber motor is considered to be basic subject matter of the motor and would not preclude classification in Class 91. Also see (2) Note, in
55, of Class 91. For statement of the line between Class 74 and Class 92, see section III of the class definition Class 92. 92, Expansible Chamber Devices, see (3) Note above for the relationship of Class 91 and Class 92.
123, Internal-Combustion Engines. The line between Class 91 and Class 123 is one of disclosure. Thus, any patent which has at least one embodiment of the invention which is disclosed as an internal combustion engine, and which has a claim specific to such embodiment, and in which the claim includes control of the motive fluid, is classified in Class 123 even though the motive fluid control is not necessarily limited to internal combustion operation.
137, Fluid Handling,
82+, for pressure modulating relays or followers for expansible chamber motors. The positive inclusion in a claim of the expansible chamber motor which is controlled by the pressure modulating relay or follower precludes classification in Class 137 and causes classification in
Class 91. See, for example, subclasses 3, 47+ and 52 of Class 91. See subclasses 87+, 455+ and 561+ for self proportioning or correlating systems, line condition change responsive valves and multiple or multi-way valves for expansible chamber motors, respectively. The positive inclusion in a claim of the motor which is being controlled by the valve means precludes classification in Class 137. The inclusion in a claim of a cylinder in combination with a valve will not exclude a patent from Class 137 on the basis that a cylinder is the equivalent of a flow path being controlled by the valve. However, where a cylinder is claimed as having passages leading to or ports present in opposite ends thereof (as in a double acting motor) the patent is excluded from Class 137. Also see (2) Note in section I above.
172, Earth Working, appropriate subclasses, and especially
2+, 464-466 and 491 for expansible chamber motor operated or adjusted implements and see the reference to Class 91 in the Search Class section of Class 172 for a statement of the line.
173, Tool Driving or Impacting, appropriate subclasses for an expansible chamber fluid motor in a claimed combination peculiar to tool driving, such as a tool drive means combined with a tool impacting, work cleaning, tool advancing or manipulating handle feature. See the class definition of Class 173 for a complete description of the subject matter provided for therein. Also see the reference to Class 91 in section IV of the class definition of Class 173.
180, Motor Vehicles,
53.1+, for vehicles with power take-off means from the vehicle motor to a nominally claimed load.
187, Elevator, Industrial Lift Truck or Stationary Lift for Vehicle, especially
215+, for an expansible chamber fluid motor and its control in claimed combination with a more than named stationary lift for raising a vehicle in its entirety between spaced vertical positions, and subclasses 272+ for an expansible chamber fluid motor and its control in claimed combination with a more than named load-underlying support surface (e.g., external load support guide structure which is not necessary to the fluid motor internal drive, particular load-underlying support structure, elevator counterbalances). 251, Valves and Valve Actuation, appropriate subclasses for valves and valve actuators for expansible chamber motors. The positive inclusion in a claim of the motor which is being controlled by the valve precludes classification in Class 251. The inclusion in a claim of a cylinder in combination with a valve will not exclude a patent from Class 251 on the basis that a cylinder is the equivalent of a flow path being controlled by the valve. Also see (2) Note in section I
above.
415, Rotary Kinetic Fluid Motors or Pumps, appropriate subclasses for a rotary motor operated by a confined or directed fluid but not inclusive of "expansible chamber" type classifiable in Class 418, Rotary Expansible Chamber Devices.
417, Pumps, appropriate subclasses for expansible chamber pumps. Many expansible chamber devices, are capable of use either as a pump or a motor without modification, the only difference being whether pressure fluid is introduced, and mechanical power produced (motor) or mechanical power is introduced and pressure fluid produced (pump). The following criteria will determine original classification if a patent: (a) Where the disclosure is that the device can be used as a pump or motor, classification in Class 91, will result if the device is claimed as a motor or alternatively as pump or motor, or generically as an expansible chamber device, for example. If such a device is claimed as a pump classification will be in Class 417. (b) Where the device is solely disclosed as a pump, classification in Class 417 will result whether claimed generically or specifically. (c) Where the device is solely disclosed as a motor, classification in Class 91 will result whether claimed generically or specifically. (d) Where the device is disclosed and claimed generically, classification in Class 91 will result. (e) For an exception to this general line see
269+, of Class 417 and (1) Note in subclass 269 for the line between the art classified thereunder and the art in Class 91, subclasses 472+.
475, Planetary Gear Transmission Systems or Components, for planetary gear transmissions, per se. The same line exists between Class 91 and Class 475 as exists between Class 91 and Class 74.
477, Interrelated Power Delivery Controls, Including Engine Control, for interrelated control between an engine and a transmission, clutch, or brake. Class 477 was formed from patents in Classes 74 and 192 and so the same line exists between Classes 91 and 477 as exists between Class 91 and Classes 74 and 192.
375+, for expansible chamber motor driven pumps. The claiming of the pump by name only is not sufficient to exclude a patent from Class 91, the pump or piston and cylinder being considered a nominal load or the equivalent of a crosshead and guide for the motor.
GLOSSARY:
See (3) Note of subclass 418 of Class 91 for definitions of terms applicable to subclasses 418+ only.
CYLINDER A rigid external member which permanently surrounds the piston, the latter constituting a relatively moving wall for the expansible chamber, the other walls of which are formed by the cylinder, and the cylinder ordinarily including the abutment or reaction surface against which the motive fluid acts or the piston forming the abutment for the cylinder when the cylinder is movable and the piston fixed. However, the abutment or reaction surface for the piston need not necessarily be formed by the cylinder, but may be formed by a second relatively movable opposed piston within the cylinder. If the piston withdraws from the cylinder merely to control the motive fluid, the piston is still considered to be permanently surrounded by the cylinder.
DISTRIBUTOR
Means which comprises or includes a part which is movable relative to the working member of a cyclically operable motor to control a motive fluid port or passage in such a manner as to cyclically control inlet and/or exhaust flow of motive fluid to or from the motor. The distributor need not entirely cut off the motive fluid flow, but may cyclically control the amount of flow (i.e., throttling).
MOTIVE FLUID
The fluid (expansible or inexpansible) which is introduced into or withdrawn from a working chamber of the motor to cause the working member to move. The term "motive fluid" applies to the fluid from the point of origin to the point of disposal. Fluid which is withdrawn from the motive fluid supply to perform some other motor function, such as motor valve operation, is still considered to be motive fluid even though said fluid never enters the working chamber of the motor. Atmospheric air which acts upon the working member of a vacuum motor is not considered to be motive fluid unless the atmospheric air is controlled in some manner, as by valving. In a vacuum motor the fluid which is evacuated from the working chamber is considered to be exhaust motive fluid and the atmospheric air, if controlled, is considered to be inlet motive fluid.
NON-WORKING CHAMBER
A chamber of the motor which expands and contracts incident to movement of the working member, and which is neither expanded nor contracted to do work by fluid supplied to or evacuated from said chamber.
WORKING CHAMBER
A chamber into which motive fluid is introduced or from which motive fluid is withdrawn (vacuum) to cause the working member to move to perform work, the chamber expanding or contracting incident to the movement of the working member. A chamber of a vacuum motor to which atmospheric air has free
ingress and egress without any control thereof is not a working chamber. However, a chamber of a vacuum motor in which atmospheric air acts and some control is exercised over the atmospheric air is a working chamber.
WORKING MEMBER
A movable wall of the expansible chamber to which motive fluid is applied or to which atmospheric air is applied in the case of vacuum motor, said wall moving as a result of the application of the motive fluid and in so moving doing work for utilization by means other than the motor or some part thereof. In a reciprocating motor this term is generic to both a moving piston and a moving cylinder. The working member is considered to include the movable wall to which motive fluid is applied as well as all parts which are rigid therewith (e.g., piston rod). However, a pair of separate movable walls disposed in separate working chambers (i.e., chambers which are not in fluid communication during at least some part of the operation of the motor), even though rigidly connected together, are considered to be plural working members if the application of motive fluid thereto urges both walls in the same direction. A working member has a single working surface which surface may have two or more relatively movable faces so long as adjacent faces are always an extension of each other (e.g., flexible diaphragm or bellows).