Editing Pump (section)

===Priming a pump===
Typically, a liquid pump cannot simply draw air.  The feed line of the pump and the internal body surrounding the pumping mechanism must first be filled with the liquid that requires pumping:  An operator must introduce liquid into the system to initiate the pumping, known as ''priming'' the pump.  Loss of prime is usually due to ingestion of air into the pump, or evaporation of the working fluid if the pump is used infrequently.  Clearances and displacement ratios in pumps for liquids are insufficient for pumping compressible gas, so air or other gasses in the pump can not be evacuated by the pump's action alone.  This is the case with most velocity (rotodynamic) pumps — for example, centrifugal pumps. For such pumps, the position of the pump and intake tubing should be lower than the suction point so it is primed by gravity; otherwise the pump should be manually filled with liquid or a secondary pump should be used until all air is removed from the suction line and the pump casing.  Liquid ring pumps have a dedicated intake for the priming liquid separate from the intake of the fluid being pumped, as the fluid being pumped may be a gas or mix of gas, liquid, and solids. For these pumps the priming liquid intake must be supplied continuously (either by gravity or pressure), however the intake for the fluid being pumped is capable of drawing a vacuum equivalent to the boiling point of the priming liquid.<ref>{{Cite AV media |url=https://www.youtube.com/watch?v=Y99ulE85e8Q |title=NASH Liquid Ring Vacuum Pump - How It Works |date=2017-01-20 |last=Nash |access-date=2024-11-07 |via=YouTube}}</ref>

Positive–displacement pumps, however, tend to have sufficiently tight sealing between the moving parts and the casing or housing of the pump that they can be described as ''self-priming''.  Such pumps can also serve as ''priming pumps'', so-called when they are used to fulfill that need for other pumps in lieu of action taken by a human operator.