What does the pyloric sphincter do?

According to the National Center for Biotechnology Information, the function of the pyloric sphincter is to facilitate emptying of the contents of the stomach. The NCBI article states that the pyloric sphincter plays a passive role in evacuating gastric contents.

The rate at which this occurs varies depending on the food being digested, as well as other factors such as distension of the related duodenem. Inner Body describes the pyloric sphincter as a circular structure with strong fibers and muscular walls, which also functions as a valve to keep food that has passed into the intestines from passing back into the stomach.