Originally Posted by Chopjaw
couple of questions?
1. What's the purpose of using the ball valve's and piping on the outside.
2. Some have vent holes, some just have piping.
The ball valve gives you an easy way to fine tune the amount of draft - and due to the nature of the handle - it is fairly easy to reproduce. You only need one valve (and two caps) to create any fraction of flow between 0-3 open holes.
That said, magnets work the same as caps, plus you can crack open a hole with one (fully adjustable). It is just not quite as easy to adjust and reproduce as the valve.
Exposed piping is to get the valve higher so you don't have to bend over.