Valve and operator therefor

A valve including a valve member having two different stable positions, the valve including two ports, each surrounded by a valve seat, the valve member engaging one of the valve seats when in one of its stable positions, and the valve member engaging the other valve seat when in the other of its stable positions, and a valve operator for shifting the valve member between its two stable positions and holding the valve member in those positions, the valve operator comprising:

• a shuttle moveable between two extreme positions corresponding to the two stable positions, respectively, of the valve member,
• means for transmitting movement of the shuttle to the valve member,
• a first spring for urging the shuttle toward one of its extreme positions,
• a second spring, stronger than the first spring, for urging the shuttle toward its other extreme position, and
• means for selectively rendering the second spring ineffective with respect to the shuttle,
• whereby, when the second spring is ineffective the first spring causes the valve member to assume one of its stable positions, and when the second spring is not ineffective the second spring causes the valve member to assume the other of its stable positions.