Since there is only one stop on the pedal, the stop knob for the Soubasse actuates a valve that shuts off the air supply to the entire pedal windchest. The valve works the same way as a slider. The side pieces are made the same thickness as the slider but there is a piece of .015 shim stock installed on each side to give adequate clearance for the slider to move freely. Here's the valve disassembled:

I added a soft spring to the side to give enough friction to hold the slider in the up position:

Here's a series of photos showing the valve closing:

And here's the valve installed. The position of the slider is controlled by a stop knob:

Click here for a movie of the valve in action.