A magnetic-latching of either of the selected operating positions of a two-position valve utilizes a generally toroidal magnetic circuit that is established by spaced inner and outer annular walls which are connected at their axial ends, with an inlet-port fluid-flow connection at one end to the interior...http://www.google.com/patents/US5375811?utm_source=gb-gplus-sharePatent US5375811 - Magnetic-latching valve
