(under subclass 368) Apparatus including a train of at least three intermeshing toothed gears, one connected to the signal input means, another connected to the valve means and a third connected to the working member to provide the feedback signal, operation of the signal input connected gear causing operation of the valve means connected gear while the working member connected gear is stationary, and operation of the working member causing operation of the valve connected gear while the signal input connected gear is stationary.
