When rain washes across parking lots and streets, it picks up oil from leaky engines. The water enters the storm drain system. Rather than just releasing oil laden water to the environment, a separator is placed before the outlet. The University of Mississippi recommends 20 square feet of surface area in the separator for every 10,000 square feet of drainage area. To put this into perspective, a parking lot measuring 100 feet by 100 feet has 10,000 square feet of surface area. A separator tank's surface size should measure 4-feet wide by 5-feet long.
A ship's bilge water collects oil from engines and other leak runoff. Ships have to discharge this water into the ocean. Without a separator, all the oil would be discharged as well. The Massachusetts Maritime Academy states that ship's bilge water discharge can contain no more than 15 parts per million (PPM) of oil. Parts per million is a unit of measurement. For example, in a million gallons of water, only 15 gallons are allowed to be oil. Engineers design separators utilizing various methods, such as screen filtering. The overall goal of 15 PPM, however, must be met before any bilge water discharge takes place.
Diesel fuel is a type of oil. If any water is in the fuel, the engine will not run. Water will damage the delicate internal components, since rust will set in. Water enters into the fuel system by natural moisture in the the air condensing into the fuel. Therefore, all diesel engines must have an oil water separator in the fuel system, to completely remove all the water. Engineers design separators to work by different methods, but all rely on the principle that oil rises to the top of water. The inlet and outlet is at the top of the separator, and at the bottom is a spigot. Internal filters direct the fuel oil to the top, and water collects on the bottom. A technician has to open the spigot regularly to drain off the water. Some computer controlled separators have an electrically controlled valve at the bottom, with a sensor. When the sensor detects water, the computer opens the valve and the water is drained to a holding tank for further processing.