Sample valve: 
When turn the hand wheel clockwise, the valve shaft and seal rise up. Atthis time, Valve is open for sampling. When turn the hand wheel anti-clockwise, the valve shaft and seal go dowm, at the time, the valve is closed.

Yogurt Sampling Valve:  
The valve seat opens inside so that it can avoid opening by accident due to much pressure in the pipes.
The valve is normally closed (through close of spring). the valve is oprn as soon as pushing the handle with hand and closed then loosing up.
The design of completely drainage water is to avoid remains inside the valves.