The U.S. 1970 Clean Air Act (CAA), amended in 1977 and 1990, legislated major reductions of atmospheric hydrocarbon pollution. Studies have shown that up to 95% of emissions from the transportation of petroleum could be contained for recycling. As a result, the petroleum industry began to seriously examine gasoline vapor emissions and controls. Although attempts have been made to develop top-loading vapor recovery systems, the advent of bottom-loading provided superior vapor recovery technology. Today, bottom-loading vapor recovery technology dominates and has been applied worldwide.
In the drive to improve workplace safety and lower operating costs, North American oil companies partnered with the transportation industry to develop the concept of bottom-loading petroleum tank trucks. Starting in the 1950s, the concept led to industry-wide adoption of a new tanker product: a valve that permitted both loading and unloading through a common valve located at the bottom of the tanker. This valve has a special nose design, which, along with a mating dry break coupler (on the terminal loading arm), allows for the fast, safe connection, and transfer of petroleum from the terminal to the tank truck.