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)
Cold weather also does not cause colds -- at least not directly. Despite its name, the common cold is not caused by cold. It doesn't have any effect at all, says Tallman. In fact, you may be more likely to catch your death of cold indoors, where it's warm and crowded than outdoors in the chilly air.