Liquid source switch-over device

A valve assembly having a first inlet connectable to a first source of flowable material, having a second inlet connectable to a second source of flowable material and having an outlet, the device comprising:

• a switching cylinder in fluid communication with the inlets;
• a spool moveable within the switching cylinder, whereby pressure differences between the sources of flowable material position the spool in a first position that promotes flow of flowable material from a first one of the sources through a first one of the inlets and to the outlet;
• and
• a catch apparatus in fluid communication in part with the outlet and which, when in communication with the flowable material from said first one of the sources, inhibits movement of the spool,
• whereby when said first one of the sources is depleted, the switching cylinder is depressurized at said first one of the inlets and said outlet, thereby releasing the catch apparatus, and
• pressure of flowable material from a second one of the sources at said second one of the inlets causes the spool to move thereafter to a second position that promotes flow of the flowable material from the second one of the sources through a second one of the inlets and to the outlet, with the catch apparatus now in communication with the flowable material from said second one of the sources and inhibiting movement of the spool once more.