POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS

**Definition:** This place covers:

Pumps or compressors which cause a fluid to move by trapping a fixed amount of said fluid, and then forcing or displacing the trapped fluid into discharge means.

Reciprocating pumps or compressors causing the fluid to move using one or more oscillating pistons, plungers or flexible working members, i.e. membranes, diaphragms or tubes.

**Limiting references (this place does not cover):** - Machines for liquids, or pumps, of rotary-piston or oscillating-piston type -> F04C - Non-positive-displacement pumps -> F04D - Pumping of fluid by direct contact of another fluid or by using inertia of fluid to be pumped -> F04F

**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: A 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: A 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, so that 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: 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