Bilge pumps are placed in the hold or lower levels of a ship to remove accumulated water from the lowest portions of the vessel. Ship or boat owners install bilge pumps at the lowest possible level of the ship below the sea surface in an area called the bilge. The bilge forms the joint where two sides of a ship or boat connects. Bilge pumps are essentially electrical water pumps that are wired into the ship's main electrical system or to a marine battery. This constant supply of electricity allows the pump mechanism to engage if the sensor recognizes rising water levels or if the captain engages the bilge pumps.
Priming the Pump
Some bilge pumps require priming to encourage the draw of water through the pump and out the discharge pipe. When bilge pumps aren't used, air enters all the compartments inside the casing. This includes the impeller fan's blades. Priming involves submerging the pump below the water line and allowing the pump to run to remove the air inside the pump. Most bilge pumps have a shut-off valve to close the discharge line to encourage strong suction. It's important to clean any debris from the bilge water to prevent clogging the intake valve of the pump.
Drawing in Water
Bilge pumps have a number of component parts that work in conjunction to expel water from the bilge. Inside the bilge pump, an impeller rotates as water enters through its middle. The impeller converts the kinetic energy of the water to increase the rotation of this multi-blade, fan-like part. The impeller forces the pressurized water into a channeled casing. In general, the increased speed of the impeller increases the amount of pressure within the casing.
Discharge of Water
Once the impeller spins to force the water into the casing, the water must have a place to go. The water travels through the casing and is released through a pump discharge tube back into the waterway. Larger ships have a series of bilge pumps installed throughout the hold of the ship and at varying levels to deal with high levels of water when one pump becomes broken or overwhelmed when removing water.