In addition to the variable controls on the vacuum and the choice of
gauze or screening - we also control the intensity of the vacuum by
using the micro vacuum brushes at a 45 degree angle to further reduce
the vacuum.  Using the vacuum tools (drapery brushes, etc) at an
angle (sometimes turned almost parallel to the surface) allows more
air intake and is much easier to control than trying to maintain the
tools some fraction of a distance above the textile.  Choice of type
and length of bristles is also important.  Alternatively, carpet
cleaner equipment shops also sell a short tube with holes covered by
a slider that is placed in line (it sticks into the hose cuff) to
regulate the vacuum further by opening and closing the holes.  We
also trim the bristles on the vacuum brushes to produce tools
suitable for a variety of situations.

On one of our very powerful Roots blowers for the vacuum table and
the vacuum spotting board, the vacuum is controlled with a three-way
ball valve that can be easily adjusted to pull different amounts of
air from a side line (with a muffler and silencer on it) - thereby
breaking and decreasing the vacuum.  The large motor for the blower
is a fixed speed motor and cannot be regulated with variable voltage.

David Walker
Talisman Restoration, Inc.

On Mar 30, 2007, at 8:15 AM, Ballard, Mary wrote:

> With various volunteers & interns, a comparison of the suction
> level of
> vacuum cleaners (Rainbow & Nilfisks especially) across various
> settings
> & machines has been a concern for a long time. Finally, we borrowed
> with
> a manometer and anemometer and started to test various settings, hand
> positions, etc. We found that the distance the tip of the nozzle was
> held above the textile (or net) was more important than the suction
> level. If you press the nozzle of the vacuum cleaner against the
> textile
> you are running it at a suction level 4 times (400%) that of your
> colleague, no matter what the setting. Keeping the end of the nozzle
> about the width of a pencil above the textile was the most important
> factor in uniformity. Go figure! See
> http://www.si.edu/mci/english/research/technical_studies/
> gently_vacuumed
> .html So when you finally get your suction under control, you might
> want
> to borrow an anemometer from an industrial hygienist and measure your
> actual suction power.
>
> Mary W. Ballard
> Senior Textiles Conservator,
> Museum Conservation Institute, Smithsonian Institution
> 4210 Silver Hill Road, Suitland MD 20746 U.S.A.
> tel: 301-238-1210 fax: 301-238-3709
> email [log in to unmask]
>