POSITIVE-DISPLACEMENT ENGINES DRIVEN BY LIQUIDS

**Definition:** This place covers:

Engines with reciprocating pistons or rotary or oscillating pistons wherein the working fluid is a liquid.

**Glossary:** - Pump: Device for continuously raising, forcing, compressing, or exhausting fluid by mechanical means - Machine: Device that could equally be both 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 pumps: Pumps using pistons or other mechanical members to displace a working fluid in a working chamber, the dynamic effect on the fluid being of minor importance - Positive displacement engines: 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 movement of mechanical members, e.g. pistons transmitting the energy, the dynamic effect of the fluid being of minor importance - Oscillating piston machine: Positive-displacement machine in which a fluid-engaging, work-transmitting member oscillates, e.g. a vane piston swinging back and forth about a fixed axis - Reciprocating piston: Fluid-engaging, work-transmitting member of an reciprocating-piston type machine or pump that slides alternately back and forth usually along a straight line or path - Rotary piston: Fluid engaging, work-transmitting member of a rotary-piston machine or pump that can completely rotate about a fixed axis or about an axis moving along a circular or similar orbit when operating, e.g. rotor having vanes or teeth - Free-piston machine: A linear , "crankless" reciprocating piston machine in which the piston motion is not controlled by a crankshaft but determined by the interaction forces from the fluid pressure in the working chamber, a rebound device (e.g. a piston in a closed cylinder) and a load device (e.g. a gas compressor or a linear alternator) - Rotary piston machine: Positive-displacement machine in which a liquid-engaging, work-transmitting member rotates about a fixed axis or about an axis moving along a circular or similar orbit, e.g. machine with a rotor having vanes or teeth - Cooperating members: The "oscillating piston" or "rotary piston" and another member, e.g., the working-chamber wall, which assists in the pumping action or machine's action - Movement of the cooperating members: To be interpreted as relative, i.e. one of the "cooperating members" may be stationary, even though reference may be made to its rotational axis, or both may move - Teeth or tooth equivalents: Includes lobes, projections or abutments - Internal axis type: 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 - Working fluid: The driven fluid in a pump or driving or driven liquid in a machine. The working fluid can be in a compressible, gaseous state, e.g. steam, called elastic fluid, a liquid state, or a state where there is coexistence of elastic fluid and liquid state