The self-priming dirty water pump is unique. As the name suggests, they actually have the ability to self-inspire under conditions of increased suction. They draw liquid from the tank or pit below, making it easier and safer to work than pumps working underground. Under the right conditions, they release their entrained gas and pump it by themselves, but sometimes they can't. why? What causes the self-priming pump to fail to start?
To understand why, we must understand how the self-priming dirty water pump works.
Note: Just because self-priming dirty water pump are able to draw in liquids does not mean they should start to dry! Self-priming dirty water pumps require fluid in the casing to start. Drying, even for short periods of time, can result in mechanical seal damage and pump failure.
When the self-priming dirty water pump is turned on, the impeller begins to rotate counterclockwise. An internal fluid or "initial filler" flows through the volute into the discharge chamber. Here, the air is separated from the fluid, the air is discharged through the open line or the air release line, and the fluid is returned to the impeller through the recirculation port.
When the fluid is recirculated and air is removed from the discharge chamber, a low pressure is created at the eye of the impeller. Atmospheric pressure is higher than the lower pressure generated at the eye of the impeller, so the fluid is forced to flow up the suction line.
As the fluid moves up the suction line, the air in front of the fluid is pushed into the housing and processed as the initial infusion is processed through the recirculation process. Once the fluid reaches the pump, it will operate normally.