| 摘要 |
A duct system is provided with a pair of branch conduits each having a differential pressure operated valve. Two sets of pressure ducts are connected to the duct system and a plug member is caused to shuttle back and forth, in controlled fashion to expose one or the other sets of pressure ducts to high internal fluid pressure. Each set of pressure ducts is connected so that valve-closing operation is effected for one valve and valve-opening operation is effected for the other valve in response to high internal fluid pressure in such ducts, so that the plug will cause one valve to be open when it is held in a position between the two sets of ducts until it is released to move beyond both sets of ducts thereby to cause said one valve to close, and vice versa.
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