Research Design: Strategies and Choices in the Design of Social Research

A timer control apparatus for selectively opening a valve or the like uses a conventional spring-wound clock drive mechanism slidably mounted in a housing so that its drive shaft is axially shiftable between two positions. A timer setting means is provided for turning the drive shaft to a selected time setting position and includes lost motion means to operatively engage the drive shaft only between minimum and maximum time setting positions. A time controlled lock means is provided for holding the drive shaft in either of the two axial positions and for freeing the drive shaft to be shifted to the other position upon rotation of the drive shaft to either the off position or maximum time setting position. A return spring urges the clock drive mechanism and associated drive shaft towards one of the two axial positions.