Valves are present in the veins, Explain

The heart pumps the blood through the arteries under high pressure to the tissues, due to which there is no backflow of the blood. While the veins return the blood to the heart from various organs but with less pressure, due to which there is a risk of blood flowing backwards. But the presence of valves ensures that there is no backflow in the veins. 

Hence, the veins possess the valves to prevent backflow of blood.