Which structure in the lymph vessels ensure that lymph flows in one direction

There are valves in the vessels that prevents backflow, just like in the viens. ... the lymph vessels to ensure that the flow of lymph 

Air enters through the nose (and sometimes the mouth), moves through the nasal cavity, the  pharynx, the  larynx, enters the  trachea, moves through the  bronchi  andbronchioles  till the alveoli.