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 intolerance could be due to poor overall health or it could be a symptom of a variety of health conditions, including: 1  anemia: a lack of healthy red blood cells. 2  anorexia: an eating disorder leading to loss of body fat.  hypothyroidism: the thyroid does not make enough thyroid hormones.