Ron Ginger recently asked whether it was necessary to use single or
double valves in street organs.

Firstly, the John Smith original design has no valves, blowing the
single rank of pipes directly through the tracker bar within a pressure
box.  In spite of the apparent limitations a very effective result is
obtained as the pipes are designed to operate very efficiently.

Every commercial street organ I have seen uses only a single pneumatic
stage between the tracker bar and the pipe chest.  In other words, the
primary valve actually sits in the back of the pipe chest and its
operation allows air to pass into the pipe or pipes.  A pillar box
valve of about 25 to 30 mm diameter seems to be adequate to allow
sufficient airflow to the longest bass pipe without compromising the
repetition rate.  Bleeds are usually adjustable in order to 'tune' the
action to the pipes.

Even the largest 31 note, five melody rank street organs built by the
top German and English makers still only use a single pneumatic stage.
With careful design and development, and quality manufacture, the
commercial products give the answer to the question.

I, too, have seen plans showing double pneumatic action on a small
street organ.  I suggest this may be as a safeguard against bad
manufacture by a hobbyist or an undeveloped basic design, to ensure
that the end result will still work.  A double valve action will use
more air and therefore be harder to turn.

The foregoing comments do not apply equally to the larger type of
keyless fairground organs where substantially larger pipes are being
operated from a similar sized paper roll or book.  Air supply is not so
much at a premium, being electrically supplied, and there are fewer
space constraints.  Many, or possibly most, small scale fairground
organs will have a double valve pneumatic action.  A competent organ
builder will optimise his design and not include unnecessary components
so the amateur should only follow suit if he thinks he is able.

Happy grinding from Great Britain,  Nicholas Simons.

PS: The term Monkey Organ is one of the highest insults that can be
levelled at the street organ.  What's wrong with the term street organ?
Nobody over here would call it a Monkey Organ.