Greetings,  Everyone who knows Duo-Art fears the cross valve.
Stories regarding unreliability abound.  Whether to replace them or
not is a difficult decision that every rebuilder must face at some
point.  I have been lucky so far.  Moving a piano is the most likely
cause of problems with valves that have been in a fixed rotational
position for a long time and which suddenly change.  This, however
is not what I wish to discuss in this letter.

Reproducing pianos rarely have single valve systems.  Reliable
operation over the wide range of pressures needed in a reproducing
piano have generally prompted the manufacturers to use a double-valve
system or other methods to improve valve responsiveness, such as the
Ampico ball bleed.

The Duo-Art is an exception.  Whether it was a good choice or not,
it is my belief that the designers of the Duo-Art were attempting to
improve the responsiveness by the use of cross valves.

There is no disagreement that the force to unseat a cross valve that
will pass the same amount of air as a round valve is less than that
required to unseat the round valve.  The force to unseat a valve is
determined by the area of the valve face exposed to vacuum, the weight
of the valve poppet and the contact surface of the seat.  When tests of
flow are made, it is important to consider the actual operating range
of the valve, in its intended application.  A stack valve is marginally
adequate at low vacuum pressures and this range is where valves should
be compared.

All but the worst valves will perform adequately at higher vacuum if
they perform well at low vacuum.  Measuring the flow through a valve at
high vacuum does not necessarily indicate how it will operate in the
critical low vacuum ranges.  It is likely that greater turbulence will
diminish the total flow in the cross valve.  However, since the flow is
likely to be more than adequate at higher vacuum, this is not of much
importance.

Judging a valve on the basis of how it performs at higher vacuums is
not likely to produce meaningful results.  Measurement with a heavily
sprung reservoir is not the right test.  Accurate measurement at low
vacuum is more likely to produce comparative indications that relate to
how the valve will perform in actual use.

There is a definite relationship between area perimeter, valve gap and
flow and this can be measured under conditions similar to a valve
operating in a stack.  We can be scientific and measure the performance
of valves instead of attempting to discredit the opinions of others by
quoting them out of context and distorting their arguments.

Whether increased performance is worth the risk of increased maintenance
can be better determined once the performance is accurately evaluated.

I have the tools to accurately measure flow in real time, under actual
playing conditions.  I do not have the time to construct a model of
each of the valves which should be compared but will find time to
evaluate them if someone else has the time to construct the models.

Pneumatics, loaded to simulate the piano action, fitted with each of
the valves to be compared, can be driven with identically timed signals
and real time graphs of flow to the pneumatic can be produced.
Additionally the pneumatics can be fitted to operate an actual piano
action so as to limit the performance comparison to the conditions
which are relevant.

If anyone wants to collaborate on such a project, please contact me.

Best regards,
Spencer Chase
Laytonville, Calif.
http://www.spencerserolls.com/