Pump priming
 
Pump Priming is the process of removing air from the pump and suction line. In this process the pump is been filled with the liquid being pumped and this liquid forces all the air, gas, or vapour contained in the passage ways of pump to escape out. Priming maybe done manually or automatically. Not all pumps require priming but mostly do. There are Self Priming Pumps and also some layout situations where priming is not required.
 
Priming a pump is probably the first and one of the most important thing one should do before operating it. Not priming a pump or not doing it properly makes majority of pump problems. Any problem in pump due to lack of priming may cause financial impact due to pump maintenance and the downtime of piping system due to a malfunctioning pump.

 
Why Priming is Required?
Priming reduces the risk of pump damage during start-up as it prevents the the pump impeller to becomes gas-bound and thus incapable of pumping the desired liquid.

For reliable operation, pumps must first be primed; that is, air or gases to be expelled from the suction and impeller eye area and replaced with liquid to be pumped. The pump would not function properly when not completely filled with liquid. Along with compromised performance, not priming the pump and allowed to run without fluid, it will overheat the pump system and there will be a danger of damage to critical internal pump components.
 
When Priming is Not Required?
Priming is only not required when the pump is either capable of removing air and gases from itself (also known as Self Priming Pumps) or the layout conditions are so much favourable that the pump will be always completely filled with the liquid to be pumped. Few such conditions are detailed out below.
  • Priming is not required when pump is submerged (Submersible or Vertical Sump Pumps).
  • Priming is not required when the pump is at a lower elevation than the supply and this ensures that pump suction will be completely filled with liquid at all times (known as “Flooded Suction Condition”).
  • Self Priming Pumps.
Methods of Priming Videos
Priming of a pump can be achieved by either layout consideration, or by means of some external arrangements that ensures priming or by use of Self Priming Pumps. Few of the external arrangements that ensures priming of a pump are detailed out below.
Manual Priming
In this method of pump priming, liquid is poured in the pump suction. This can be achieved by pouring liquid directly in suction or with the help of other devices like a funnel and the pump will be manually primed with a gravity feed. While priming is being done, all the air escapes through air vent valve.

 
Priming by Installing Foot Valve
In this method of pump priming, a foot valve (functioning as a NRV) is installed in the suction piping to insure that the liquid will not drain from the pump casing and suction piping once the pump stops operating. A foot valve is a form of check valve installed at the bottom, or foot, of a suction line. When the pump stops and the ports of the foot valve close, the liquid cannot drain back from pump suction if the valve seats tightly. Keep in mind that these foot valves have a nasty habit of leaking.