“Its like a valve that allows food into the stomach, but doesnt allow the stomach acid back out. “
That’s incorrect, Kassee.
The stomach sits just below the diaphragm. This is a sheet of muscular tissue that separates the bottom of the chest cavity from the cavity where the stomach and intestines reside. The diaphragm moves up and down, expanding the chest cavity and enabling you to breathe.
There is a gap in it where the oesophagus (the tube from your mouth to your stomach) passes through. Sometimes the stomach distends and pushes its way through the diaphragm and causes damage to it. That is a Hiatus Hernia. (“Hiatus” means gap).