1. Preferably, a screw jack is used to adjust the vertical height of the valve.

2. A raise/lower lever actuates a powered screw jack giving the child seat height variation from ground level.

3. The fore-aft relationship of the rails may also be selectively adjusted by a motor driving a horizontally oriented screw jack.

4. The ground floor panels are supported by posts screwed into the ground or alternatively by screw jack members secured to footings and accessed for screwing adjustment through holes in the top of the panel.