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MMD > Archives > February 2009 > 2009.02.12 > 03Prev  Next

Good Vacuum Sources
By John A. Tuttle

Hi All,  I've been meaning to write about this subject for some time
because there seems to me quite a bit of confusion about what actually
constitutes a "good" vacuum source.  I suppose the best way to approach
the conversation is to compare it to a water hose.

Think of it this way -- if you have a 1/4" water hose, the amount of
water pressure you have going into the hose isn't very important because
only so much water flow can get through the hose.  That's because the
small size of the hose restricts that total amount of water that can get
through.  Use a 2" water hose at the same pressure, and a lot more
water will get through.  Use a 4" hose and you see why it can be used
to put up a house fire.  It's all about the volume of water in relation
to the size of the hose.

(Electricity works the same way.  No matter how much voltage you have
at one end, only so many amperes can flow through the wire before it
will burn up.  That's because only so many electrons can safely pass
through the wire at any given moment in time.)

Vacuum is no different.  Take 30" of vacuum and use a 1-1/2" hose,
and then try to operate that same system on a hose that's only 1/2"
in diameter.  What you soon discover is that there are a variety of
different player systems.  Some require a lot of air flow at a lower
vacuum level, and others require less air flow at a higher vacuum
level.  When you break it all down, it has a tremendous amount to do
with the size of the bellows (pneumatics) that are used in the overall
player system.  Simply put, bigger bellows need more air flow, and not
necessarily a higher vacuum level.

Naturally, applying a higher vacuum level through a smaller hose
will cause more air to flow through the tube, but everything reaches
a maximum at some point.  Therefore, the real key to testing a system
is to use the smallest hose possible at the lowest vacuum level
possible to get the system to work properly.

Just recently, I encountered a gentleman who used a standard vacuum
pump to 'fix' his leaking player system.  After numerous attempts, he
claimed that the pump just wasn't strong enough to do the job, and he
wanted a more powerful pump.  I asked for pictures of how the system
was hooked up to the player and saw that he was restricting the air
flow with a valve that was less than 1/2 the size of the flange at the
output of the pump.

I explained the problem he created using simple mathematics, and
low-and-behold, he had to reduce the speed of the vacuum pump by about
one-half to keep the volume of the music from blasting him out of the
house once he removed the 'restriction'.

It all boils down to this -- you must understand the needs of the
system before you can make an educated decision about how much vacuum
is needed to make the system function properly.  That's why I invented
the 'suck' tests, and other tests that are at  It's
absolutely necessary to understand how much air flow is required to
make the system function before you know if it's working correctly.
And if you can't grasp that idea, fixing the system will be an exercise
in frustration.

John A Tuttle
Brick, New Jersey, USA

(Message sent Thu 12 Feb 2009, 09:15:11 GMT, from time zone GMT-0500.)

Key Words in Subject:  Good, Sources, Vacuum

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