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 Feet, Many Culprits. If your toes are always cold, one reason could be poor blood flow -- a circulatory problem sometimes linked to smoking, high blood pressure, or heart disease. The nerve damage of uncontrolled diabetes can also make your feet feel cold. Other possible causes include hypothyroidism and anemia.