for self-priming. So once a self-priming pump has run once, it will automatically contain enough water to self-prime. However, when starting an empty self-primer, the pump must be primed manually.
Self-priming pumps are designed with a large reservoir surrounding the pump casing. When the pump is energized it begins to attempt to pump the water in the casing that was retained after the last time the pump ran. As the water is pushed out of the casing, air is drawn into the suction of the pump. Since the casing is not full of water, the water being pumped exits the casing but does not exit the reservoir. Instead, the water drains back into the casing, but the air carried with the water separates and is pushed out of the pump as more air is pulled into the suction of the pump.
This process repeats itself and more and more air is drawn out of the suction line until the air in the suction line has been completely purged. Once that happens, the reservoir begins to fill. Once the reservoir is full the pump begins to discharge water.
Different submersible pumps can lift water different distances. Repriming lift capabilities commonly range from 10 to 25 feet depending on the pump model and it’s operating speed. It’s important to consult with the manufacturer of a self-priming pump or to review the literature provided by the manufacturer to ensure that the pump you have in mind can lift water as far as you plan on lifting it before designing a pumping system around it.
What are Self-Priming Pumps Used For?
Self-primers are commonly used in sewage lift stations, where raw sewage is pumped into a treatment facility. They are also commonly mounted on portable skids and used to pump stormwater and for dewatering of construction and mining operations. When used to dewater construction sites, self-priming pumps are often referred to as trash pumps – a reference to the fact that they are capable of pumping the debris that is typically found at construction sites.
If you want to learn more about how self-priming pumps work, we recommend this article from DJ Gongol & Associates.