In this subsection, subclasses or groups designating "engines" or "pumps" cover methods of operating the same, unless otherwise specifically provided for.

In this subsection, the following terms or expressions are used with the meanings indicated:

"engine" means a device for continuously converting fluid energy into mechanical power. Thus, this term includes, for example, steam piston engines or steam turbines, per se, or internal-combustion piston engines, but it excludes single-stroke devices. "Engine" also includes the fluid-motive portion of a meter unless such portion is particularly adapted for use in a meter;

"pump" means a device for continuously raising, forcing, compressing, or exhausting fluid by mechanical or other means. Thus, this term includes fans or blowers;

"machine" means a device which could equally be an engine and a pump, and not a device which is restricted to an engine or one which is restricted to a pump;

"positive displacement" means the way the energy of a working fluid is transformed into mechanical energy, in which variations of volume created by the working fluid in a working chamber produce equivalent displacements of the mechanical member transmitting the energy, the dynamic effect of the fluid being of minor importance, and vice versa;

"non-positive displacement" means the way the energy of a working fluid is transformed into mechanical energy, by transformation of the energy of the working fluid into kinetic energy, and vice versa;

"oscillating-piston machine" means a positive-displacement machine in which a fluid-engaging work-transmitting member oscillates. This definition applies also to engines and pumps;

"rotary-piston machine" means a positive-displacement machine in which a fluid-engaging work-transmitting member rotates about a fixed axis or about an axis moving along a circular or similar orbit. This definition applies also to engines and pumps;

"rotary piston" means the work-transmitting member of a rotary-piston machine and may be of any suitable form, e.g., like a toothed gear;

"cooperating members" means the "oscillating piston" or "rotary piston" and another member, e.g., the working-chamber wall, which assists in the driving or pumping action;

"movement of the co-operating members" is to be interpreted as relative, so that one of the "co-operating members" may be stationary, even though reference may be made to its rotational axis, or both may move;

"teeth or tooth equivalents" include lobes, projections or abutments;

"internal-axis type" means that the rotational axes of the inner and outer co-operating members remain at all times within the outer member, e.g., in a similar manner to that of a pinion meshing with the internal teeth of a ring gear;

"free piston" means a piston of which the length of stroke is not defined by any member driven thereby;

"cylinders" means positive-displacement working chambers in general. Thus, this term is not restricted to cylinders of circular cross-section;

"main shaft" means the shaft which converts reciprocating piston motion into rotary motion or vice versa;

"plant" means an engine together with such additional apparatus as is necessary to run the engine. For example, a steam engine plant includes a steam engine and means for generating the steam;

"working fluid" means the driven fluid in a pump and the driving fluid in an engine. The working fluid may be in a gaseous state, i.e., compressible, or liquid. In the former case coexistence of two states is possible;

"steam" includes condensable vapours in general, and "special vapour" is used when steam is excluded;

"reaction type" as applied to non-positive-displacement machines or engines means machines or engines in which pressure/velocity transformation takes place wholly or partly in the rotor. Mmachines or engines with no, or only slight, pressure/velocity transformation in the rotor are called "impulse type".

In this subsection:

cyclically operating valves, lubricating, gas-flow silencers or exhaust apparatus, or cooling are classified in subclasses F 01 L, F 01 M, F 01 N, F 01 P irrespective of their stated application, unless their classifying features are peculiar to their application, in which case they are classified only in the relevant subclass of classes F 01 to F 04;

lubricating, gas-flow silencers or exhaust apparatus, or cooling of machines or engines are classified in subclasses F 01 M, F 01 N, F 01 P except for those peculiar to steam engines which are classified in subclass F 01 B.

For use of this subsection with a good understanding, it is essential to remember, so far as subclasses F 01 B, F 01 C, F 01 D, F 03 B, and F 04 B, F 04 C, F 04 D, which form its skeleton, are concerned:

the principle which resides in their elaboration,

the classifying characteristics which they call for, and

their complementarity.

Principle

Characteristics

Complementarity

For the same kind of apparatus in a given genus, the characteristic of "working fluid" associates:

For the same kind of working fluid, the "apparatus" characteristic relates subclasses in the same way as considerations of relative generality.