In MMD #970422 I described some preliminary tests that I  carried out on
some Ragtime MIDI air valves. Since that time I have received some
modified valves and have carried out some additional testing.

Since few people have seen the valve and it is I believe of a unique
design,a description may be in order. The valve body is injection
moulded PVC but it is fitted with a soft elastomeric seat. The valve is
remarkably tiny--No more than 3/8 " dia by 7/8"long. An 1/8" dia spigot
sticking out from the side provides a tubing connection. A 5/32' dia T
piece is available to glue on to the spigot so the valve can be if
desired  fitted 'in line" in the tracker bar tubing.

In the valve a tiny permanent magnet about 1/8 dia by 1/4" long acts as a
valve poppet. In the de-energized position the magnet is attracted to
the hollow valve coil core situated behind the valve seat. The attraction
of the magnet to the hollow core effectively seals the seat against
leakage. When the valve coil is energized the electro-magnetic force
overcomes the attraction  the magnet to the core and repels it. The
valve thus is opened allowing air thru the hollow core into the valve.

The valve is designed so that vacuum from the pouch/bleed will be on top
of the valve seat. This means that the vacuum will tend to opens the
valve rather than suck it shut. In other words the magnetic attraction
and the vacuum are opposing forces. The consequence of this is the
voltage required to operate the valve is independent of the vacuum
level.

The valve coil is apparently rated for 12 volts continuous operation. The
valve appears to work equally  well at 9 volts or even 7.5 volts.

In the absence of sophisticated  electronic test equipment I could only
carry out some simple cycling speed tests. A visual/auditory test would
indicate that the valve can open and close in excess of 15 times per
second. When tubed into the tracker bar of my piano it can play a note
10 times a second.(stack vac 27") This of course is more a test of my
piano than of the valve. The valve appears to operate equally well in
any orientation.

Air flow measurements ---All done using 6''vac

        Valve open---220 cubic inches per minute

        Valve open (top bumper removed in valve to allow magnet extra travel)
        270 cubic inches per minute

For comparison purposes the air flow thru a 1/16 diameter piano roll hole
when located on a tracker bar is 250 cubic inches per minute.

Since a piano note will normally play when the piano roll hole is 1/3 open
or 2/3 closed it would appear that the valve  will allow more than
sufficient air flow for the operation of any piano.

My only concerns about the valve were the following:

 1) Because of the size and clearances in the valve I thought dirt
    ingress might  be a problem. This has hopefully been addressed
    in the modified valve where  the hollow core air inlet  is covered
    with a felt filter.  (for pressure operation there is apparently
    available a fitting/connector which will fit over the filter.

 2) Air leakage across the seat when the valve is closed  A soft seat
    in the modified valve seems to have eliminated  these problems.
    Any small leakage that does exist  does not seem to have any
    effect on the valves  function. I have carried out a number of
    leakage measurements but I am not convinced that they have any real
    significance so I have not listed them here.  The valve appears
    operate normally  up to at least 45" vac .

I have been talking to Ken Caulins of Ragtime. He has asked me if it was
possible to point out in this posting his replacement policy. He stated
that when components etc are redesigned/improved  he will exchange the
old components for new. He also said that he is building a larger
version of the valve for a dance organ and that he has built a small
monkey organ using an even larger model of the valve to directly operate
the pipes.

I hope the above will be of some use. If I ever get around to use these
valves in a real instrument I will do another posting.

Phil Dayson