Self-priming centrifugal pumps are unique. As the name suggests, they have the ability to prime themselves under suction lift conditions.  They draw fluid up from tanks or pits below, making them easier and safer to work on than those that work below ground. Under the right conditions, they’ll free themselves of entrained gas and function normally on their own, but sometimes, they can’t. Why? What causes failure to prime in a self-priming pump?
In order to understand why we have to understand how a self-priming pump works.

Just because they’re able to pull fluid into them, doesn’t mean that they should start up dry!! Self-priming pumps need fluid in the casing to get started. Running dry, even for a short while, will cause damage to the mechanical seal, and pump failure.

Once the pump is turned on, the impeller begins to turn in a counter clockwise rotation. The fluid inside, or the “initial prime”, flows through the volute into the discharge cavity. Here, the air and fluid separate, the air evacuates through an open ended line, or air release line, while the fluid returns to the impeller through a recirculation port.

While the fluid is recirculated and the air is removed from the discharge cavity, low pressure is being created at the eye of the impeller. Atmospheric pressure is higher than the lower pressure created at the eye of the impeller, thus fluid is forced up the suction line.

As fluid moves up the suction line, the air ahead of the fluid is pushed into the casing and handled as the initial prime was handled through the recirculation process. Once the fluid arrives in the pump, it operates as normal.

Having a pump that won’t prime, loses its prime, or is slow to prime? Ask us about it at water pump dubai We gladly provide technical assistance to businesses