The main reason to use self priming pumps is they are able to operate without needing an outside priming system. A centrifugal pump is incapable of pumping air and since it needs to impart velocity to water or liquid, it has to be filled before it is able to perform its functions.
Self priming pumps are designed to evacuate air from the suction line. However, before they are able to do their work it pays to keep in mind that even self priming pumps need to have enough water inside the pump casing before they can be energized. If you try and run a self priming pump while it is empty, it will cause failure of the mechanical seal as well as damage to important components. Self priming pumps will however retain just enough water in order to prime themselves. So, after they have run once, there will automatically be enough water so that the pump is able to prime itself. Thus, on the first time it is run, you will need to prime the pump manually.
Self priming pumps are used for a variety of reasons and for different applications. They can be used in sewage lift stations where the raw sewage has to be pumped into treatment facilities.
Self priming trash pumps are a variant that you need to learn about if you need to remove solids from a liquid. They are also widely used in excavation sites where the excavation is normally mixed with sand and rocks as well as sticks and other solids. The self priming trash pumps are capable of passing large pieces of debris without binding or doing any damage to the pump. They are also designed to keep large amounts of water flowing even when the water contains sludge and mud or sand or other waste materials. The nice thing is these pumps perform their functions without requiring any external assistance. There are several different self priming trash pump models to choose from. These pumps are used when there is an irregular flow condition which normally happens when some hard or soft solids are present in the water.
Low-pressure self priming pumps are normally very useful when you need to evacuate air from a pipe. These pumps are able to automatically mix air with water and then they will remove all the air present inside the pipe and make the pump ready to perform its functions.