Semilunar valves prevent backflow of blood in your ventricles.
AV valves prevent backflow of blood on your atria.
There are two AV valves. The tricuspid valve prevents backflow of blood into the right atrium. The bicuspid or mitral valve prevents backflow of blood in the left atrium.
There are also two semilunar valves. The pulmonary valve prevents backflow of blood in your right ventricle. The aortic valve prevents the backflow of blood in the left ventricle.
The flow of bllod from the right atria -> TRICUSPID VALVE -> right ventricle -> PULMONARY VALVE -> left atria -> MITRAL VALVE -> left ventricle -> AORTIC VALVE -> AORTA
Anatomically, the pulmonic valve is located in the pulmonary trunk while the aortic valve is located in the aorta.