Abstract: A power wrench opens and closes a gate valve on irrigation water pipe thereby controlling water flow from the pipe into desired areas for irrigation of crops. The power wrench includes a tubular flow member which defines a flow passage extending through a second gear and through a gripping member mounted on the second gear and engageable with the gate valve whereby water flowing from the open valve will flow through the gripping member and tubular flow member. The power wrench is power operated and includes a drive motor operative to rotate a first gear and thereby turn a second gear in engagement therewith.