Electromagnetic valve for fluid flow control

An electromagnetic valve for controlling fluid flow, comprising:

• a magnetic spherical valve member;
• a valve seat member defining a fluid outlet and having a valve seat surface (S.sub.1) on which said spherical valve member is seatable to close said fluid outlet, said fluid outlet being closable by said valve member when fluid pressure prevailing upstream of said valve member is higher than the fluid pressure prevailing downstream of said valve member;
• a central magnetic pole member having a valve contacting surface (S.sub.2) on which said valve member is contactable, said magnetic pole member being located opposite to said valve seat member so that said valve member is disposed between the valve seat surface of said valve seat member and the contacting surface of said magnetic pole member, said magnetic pole member capable of attracting the spherical valve member to separate from the valve seat surface of said valve seat member so as to open said fluid outlet, said magnetic pole member being formed with a hollow at the valve contacting surface thereof;
• and
• an expandable pressure responsive member disposed in said hollow of said magnetic pole member, said pressure responsive member being able to expand to bias said valve member onto the valve seat surface of said valve seat member so as to close said fluid outlet when the fluid pressure prevailing upstream of said valve member is lower than a predetermined level.