Question

what is the use of values in the veins

Answer 1

veins carries blood from different organs to heart

Answer 2

The main function of the valves in veins is to prevent back flow of blood.

Blood in the arteries, after being pumped by the heart, are under much higher pressure than blood in veins so there is no need for valves in arteries to prevent back flow.

Blood in veins is under much lower pressure as it is returning to the heart from the various organs and tissues and so has a risk of back flow if the valves are not present to prevent it.