A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave.
Some causes of cold intolerance are: 1  Anemia. 2  Anorexia nervosa. 3  Blood vessel problems, such as Raynaud phenomenon.  Chronic severe 1  illness. General poor health.  Underactive thyroid 1  (hypothyroidism) Problem with the hypothalamus (a part of the brain that controls many body functions, including body temperature)
The common cold and most upper respiratory infections are caused by infection with germs (viral infections). They usually get better in a few days. This leaflet gives some tips on what to do, and what symptoms to look out for which may indicate a more serious illness. cold is an infection of the nose and upper airways caused by a germ (virus). They are extremely common. An adult can expect 2-4 colds a year, and a young child about 3-8 colds a year. Many different viruses can cause a cold. This is why colds come back (recur), and immunisation against colds is not possible.