Scavenge

Scavenge (pronounced skav-inj)

(1) To take or gather (something hopefully usable) from discarded material.

(2) To cleanse of filth, as in cleaning a street (in the UK “scavenger” was once a term for a municipal street sweeper).

(3) In internal combustion engines (1) to expel burnt gases from a cylinder

(4) As “oil scavenger”, a device used to remove excess or unwanted oil from certain areas of various types of engine.

(5) In metallurgy, to purify molten metal by introducing a substance, usually by bubbling a suitable gas through it (the gas may be inert or may react with the impurities).

(6) In democratic politics (in preferential voting systems), to negotiate with other candidates or party machines to obtain preferences (usually on a swap basis).

(7) To act as a scavenger; to search (applied especially to creatures which look for food among the carrion killed by others).

(8) In chemistry, to act as a scavenger (for atoms, molecules, ions, radicals, etc).

(9) In historical UK use, a child employed to pick up loose cotton from the floor in a cotton mill.

1635–45: A back formation from scavenger, from the Middle English scavager, from the Anglo-Norman scawageour (one who had to do with scavage, inspector, tax collector), from the Old Northern French scawage & escauwage (scavenge) and the Old French scavage & escavage, an alteration of escauvinghe (the Medieval Latin forms were scewinga & sceawinga), from the Old Dutch scauwōn (to inspect, to examine, to look at).  The verb scavenge in the 1640s was first a transitive verb in the sense of “cleanse from filth” while the intransitive meaning “search through rubbish for usable food or objects” was in use at least by the 1880s and the idea of “extracting & collecting anything usable from discarded material” dates from 1922.  Scavenge is a verb, scavenged, scavengering & scavenging are verbs & adjectives, scavengeable is an adjective and scavenger & scavengerism are nouns; the noun plural is scavengers.

Lindsay Lohan: Fear of scavengers.

The noun scavenger dates from the 1540s and described originally “a person hired to remove refuse from streets” (a job which would come later to be known as a “street sweeper”, a modification of the late fourteenth century Middle English scavager & scawageour, the title of the employee of London city who originally was charged with collecting tax on goods sold by foreign merchants.  The origin of that title was the Middle English scavage & scauage, from the circa 1400 Anglo-French scawage (toll or duty exacted by a local official on goods offered for sale in one's precinct), from the Old North French escauwage (inspection), from a Germanic source (it was related to the Old High German scouwon and the Old English sceawian (to look at, inspect) and from the same lineage came the modern English “show”.  In the 1590s it came into use in zoology to refer to creatures which look for food among the carrion killed by others.  The game of “scavenger hunt” seems to have gained the name in 1937 and one form of the word which went extinct was scavagery (street-cleaning, removal of filth from streets), noted in 1851.

Oil scavenge systems

In an internal combustion engine, an oil scavenger is a device used to remove excess or unwanted oil from certain areas of the engine, typically from the bottom of the engine's crankcase or oil pan.  The oil scavenger can help to prevent excessive oil pressure or foaming, something to be avoided because in high-performance engines operating under extreme conditions, excessive pressure can collapse pistons, a destructive process.  The core of the system is a scavenge-pump (some even suction mechanisms) which draw the excess oil from the engine and directs it back into the oil pan or an external reservoir.

Internal combustion engine with dry sump and oil scavenging system.

The classic use of oil salvage is in dry sump lubrication systems in which the oil that is supplied by the pressure pump drains off the engine as a frothy, thoroughly-mixed air-oil suspension into a relatively shallow, low-capacity, sump that is often contoured around the rotating crankshaft-assembly.  In this system, there are several scavenge pump stages that pump the aerated oil from the “dry” sump and into the external oil tank that has the dual-assignment of (1) storing the major amount of the engine oil supply and (2) de-aerating the mixture being returned by the scavenge pump(s).  After lubricating the various components, the oil flows into the sump at the bottom of the engine and from here the scavenge stages of the pump retrieves the highly-aerated oil, delivering the mix through a filter and then to a centrifugal and boundary-layer air-oil separation system in the oil tank. The air extracted from the scavenge oil exits the system through the breather and the result is cool, clean oil into the external tank ready for recirculation.

Aircraft turbine engine with oil scavenging system.

Oil salvage systems are especially critical in aviation.  In car engines, used oil is able to drain down into the oil pan, where it can be circulated back through the engine or cooling system but at altitude, gravity or air pressure may not be sufficient for oil to drain on its own and for these reasons aircraft are equipped with scavenge pumps to help pull the used oil out of the engine into a reservoir for cooling, de-aerating, and recirculation.  In hard-to-empty areas that are far from the oil sump (like the rear of the engine) a scavenge pump prevents the pooling of used oil.  The aircraft scavenge pump system does not have its own power source, but operates on a designated line from the main electrical system and on bigger aircraft powered by turbines with large oil capacity, as many as six scavenge pumps may operate in unison.