Testing and Adjusting
The Air-Motor Governor
Problem 1: The air-motor speeds up when more pedal pressure is applied.
The problem is in the air-motor governor (or just 'governor') or the air-motor
control box. There are a few possible problems.
1) The material covering the governor bellow might be getting stiff
with age or leaking, preventing it from responding correctly to changing vacuum levels. If so,
recover the pneumatic with new cloth.
2) The return spring might be to tense, preventing the
governor from closing down fast enough or far enough.
(See adjustment procedure below)
3) The knife valve inside the governor might not be seating
correctly. (See below)
4) The fast re-roll port might not be closing all the way
when the unit is in 'Play'. (See below)
Problem 2: The air-motor slows down or stops as more pedal pressure is applied.
1) The return spring might be to loose, allowing the
governor to close down too much, starving the air-motor of vacuum.
(See adjustment procedure below)
2) The Stop screw is incorrectly adjusted. (See adjustment procedure below)
NOTE: Before adjusting the air motor governor, it is highly recommended that the physical location of the Tempo Slide Valve be checked. This requires removing the access panel on the Tempo Control Box and physically examining the position of the sliding valve. When correctly adjusted, the tempo slide valve should just barely cover the tempo slot (under the valve) completely when the tempo is set to '0', and it should just barely open the slot when the tempo is set to '10'. The slider should also open the slot completely when the tempo is set to '120' (or the fastest speed shown on the Tempo Indicator). If these conditions are not as described, corrective action should be taken.
To test, have someone else pump the unit evenly and depress (or collapse, or close)
the governor by hand. When depressed all the way, the motor
should almost stop (with tempo set to 60-70).
To insure that the stop screw, which prevents the governor from closing too far, is correctly adjusted, turn it 'out' one-half a turn at a time and test it again until the motor does stop when the bellow is fully closed. If the motor does stop when the bellow is collapsed fully, turn the adjustment back 'in' one-half turn. When adjusted correctly, the motor should just barely crawl when the vacuum level is high.
If the motor never comes to a complete stop, the problem is in
the adjustment of the fast re-roll valve (or the valve itself) or with the
knife valve inside the governor. To eliminate the possibility of the fast
re-roll valve as being the problem, open the control box and visually
check the position on the fast re-roll valve while the unit is in the
'play' position. It must cover the air-port 100%. Also check
the integrity of the leather. It must be smooth and slightly
flexible to make a good seal. Reassemble everything and test again.
If the motor still fails to stop, the knife valve is the problem. Open
the governor and inspect the surfaces of the knife valve. They must be
smooth and make positive contact with each other. Clean and
re-graphite as necessary. Reassemble and test. If the motor STILL
refuses to stop, there is a leak somewhere in the control box which
is allowing vacuum to bypass all the above controls. Seek out and
eliminate the leak.
To adjust the governor once all of the problems have been
eliminated, you need a Test Roll to calibrate the governor
and the control box. As a preliminary adjustment. Set the
tempo to "0". The motor should stop. Set it to "10", the roll
should 'creep'. Set it to "70" and measure the time it takes
for the roll to travel 7 feet. It should take one minute.
Now set the tempo back to "10" and pump hard. If the motor
stops, turn the air-motor governor stop screw in a bit until the motor 'creeps' along.
Once the stop screw has been set and the "0" and "10" settings
are working correctly at all levels of pressure, then the
governor spring can be adjusted. Set the tempo to "70" and test
as described above. If the unit speeds up under heavy pumping,
decrease the spring tension. Then go back and retest all the
above settings to insure they have not changed. If so, re-adjust
and then start the "70" test again.
Keep going back and forth until all three settings stay constant
at all levels of pumping pressure. These adjustments are all
interactive so any change in one will effect all three settings. It's
a delicate balancing game and all components of the system must
be in excellent condition before the final result will prove
- - - - - - - - - Added Notes - - - - - - - - - -
Sometimes it can be a pain to get the Tempo Indicator correctly
adjusted to the position of the sliding tempo valve. Usually,
there are four adjustments. 1. Where the pointer mounts on the
tempo rod. 2. Where the tempo rods is secured to the upper lever
arm. 3. Where the horizontal tempo rod connects to the lower
lever arm. (Sometimes this is solid metal, or a bent rod. So it
cannot be adjusted.) 4. An in-line adjustable link between the
lower lever arm and the Tempo Actuating Lever -Or Tempo Control
Also, the rod going into the Tempo Control Box is almost always
threaded, which allows you to make fine adjustments without
changing any of the main linkage.
The main thing to remember is the all of the levers and arms
should be positioned such that at their middle position of
rotation (or the middle of their arc), the Tempo should be
at 70. If such is not the case, the Tempo will be less linear
than designed by the manufacturer.
FYI, when you start changing the adjustments, start from the
sliding valve and work toward the Tempo Indicator, not the
other way around. Make sure the Tempo Lever (in front of the
keys) is position straight up, and that the other lever at the
rear of the rod is pointing straight down. (Sometimes the
position of the rear lever is adjustable.)
Also, understand that the function of the air motor governor
(AMG) also comes into play during the entire adjustment process.
So, getting the governor to work correctly at 70 is a prerequisite
to adjusting the "0", "10", and "70" tempos. This is because
the functions of the AMG and the Tempo Control are interactive.
So, using a test roll (or a roll that has a mark at every foot)
should be played at different pedal pressures to insure that
it stays at '70' whether you pedal softly or loudly. The
importance of this cannot be over emphasized.
BTW, normally there is no bend in the rod that connects to the
tempo slide valve. Or, if there is one, it is very near to the
sliding valve, i.e. within the last inch of the rod just above
the sliding valve.
- - - - - - - More Added Notes - - - - - - -
Keep in mind that there are three valves in a governor.
1. The tempo valve: In virtually every governor I've ever seen,
the air flow through graduated tempo slot doesn't change when
the system is in the Rewind mode unless the Tempo setting is
changed from what it was when the system was in the Play mode.
2. The governor valve: It's job is to decrease the air flow, not the
vacuum level, of the air that has already flowed past the tempo
valve, as the the vacuum level increases. Conversely, as the
vacuum level decreases, the air flow should increase to compensate
for that decrease and maintain a metered flow of air through the
air motor regardless of the vacuum level.
Also keep in mind that the governor spring is constantly trying to
counteract the level of the vacuum pressure. So, if the tension on
the spring is too great, the governor valve won't react in proportion
to an increase in the vacuum level and the air motor will speed up
as the vacuum level increases. Conversely, if the tension on the
spring is too little, the speed of the motor will slow down as the
vacuum level increases. It's a balancing act, and finding the 'sweet
spot' can be a challenge.
3. The fast reroll valve: It's purpose is to bypass the tempo and
governor valves and apply full vacuum to the air motor during the
Rewind cycle.That's why increasing the vacuum level during Rewind
will increase the speed of Rewind.
So, you can see that the fast reroll valve plays a critical roll in
determining the speed of the air motor when the system is in the
Play mode. If it's leaking even a small amount, it effectively bypasses
both the tempo and the governor valves, making it impossible to
regulate the speed of the air motor effectively.
Testing the Stack
Testing the Air-Motor
Testing the Lower Section
Testing the Tracking Device(Not Done)
This MIDI file is called "
Saved by Gabriel
" and it was created on May 17, 1998 after hearing the song on an old cassette tape. Gabriel Della Fave converted the audio cassette to Real Audio and I wrote the midi file the next day. Like many of my tunes, this one never had a title until now.