In response to Spencer Chase's inquiry about installation of tubing
"Y"s, my opinion is that it probably won't make any difference which
way it is installed.  The additional resistance to airflow from
installing the "Y" "backwards" is likely not significant.

That said, the obvious best orientation is with the two branches of the
"Y" going to each tracker bar for the best airflow.  But the
determining factor is going to be how much air has to pass through the
tracker bar and tubing in order to fill the tubing and pouch well to
lift the pouch.  If the mechanism design requires a lot of air to flow,
then having a smoother flowpath might be important.  A primary pouch
in a two-valve system will obviously require less airflow than a larger
pouch in a single-valve system.  The condition of the pouches and the
size of the bleeds are also factors.  The act of plumbing in two
tracker bars in parallel will, in itself, affect the system response,
because of the additional tubing that must be pressurized when a note
is played.  Another factor -- is this a pumper or an electrically
powered nickelodeon?  The lower the vacuum level the piano is played
at, the more important the airflow and volume becomes.  A simple test
might provide the required data to make your decision.

Ray Fairfield