Elephant trunk ventilation systems

Heather Place <conservator [at] wag__mb__ca> writes

>We are currently undergoing upgrading to our conservation lab, and
>after years of our fume extraction system not functioning correctly,
>we are working to rectify the problem. We are currently looking at
>ways to improve our existing elephant trunks and were wondering if
>anyone has any suggestions.
>
>Is there anything new on the market that anyone has experience with?
>I have heard that they now come with lights on the end. This would
>be very helpful.

Here are a few thoughts on the ventilation issue.  We work on
furniture and horse-drawn vehicles, so are facing similar concerns,
but probably on a much lower budget.  The fundamental conflict is
that if ideal ventilation is achieved, that ideal (and totally
artificial) controlled environment that we have worked so hard to
achieve will be blown through the exhaust.

There are two primary factors to consider in controlling
ventilation.  The first is the air volume and the second is
containment.  Elephant trunks attempt to isolate a small area and
contain the fumes in this area.  In order to function effectively,
there must be an adequate air volume (CFM) flowing through them.
Often, this is calculated at the opening.  However, it is virtually
impossible to work with the opening directly over the item.  As the
opening moves back from the object, the air movement at the object
surface falls off since the air is not contained as well and is
being drawn from all directions. The use of a bigger end, either
purchased or self-fabricated, improves the containment, but also
increases the surface area and volume of air that must be moved,
requiring higher CFM through the elephant trunk to be effective.  It
is very difficult to keep the trunk end close enough to the object
to be effective.

It may be possible to design a trunk end that would have a side
inlet at its bottom so that it could be placed next to the area
being worked on, yet still be very close to the object.  In this
manner, the work area would not be obstructed and the air flow could
be better contained over the work area.

The next level of ventilation to consider is placing the object
itself within the ventilation trunk.  The most common form of this
is the spray booth, which really is nothing more than a large trunk
end on a high-volume ventilation system.  The air volume normally
required for spraying finishes probably is much greater than what
would be needed for solvent fume removal.  If solvents are used over
large areas, elephant trunks will not be effective and a solution of
this type may be necessary.  Clearly, the greater the air volume
moved, the more difficult and expensive it is for environmental
control systems to operate.

A final possibility is to exhaust an entire room, but doing so will
overwhelm most environmental control systems and may significantly
increase utility costs.  This is the alternative we use, since many
of our objects are very large and we have a relatively small studio
space.  In addition, we are often treating large surface areas at
one time (e.g. coating application or removal).  For critical
solvent removal, the object can be placed directly next to the
exhaust fan, increasing air flow over it.  For more gentle solvent
removal, the object can be at the center of the room.  This method
results in compromises.  Overall air flow is not ideally high, so we
place ourselves upstream in the air flow.   We try to work with less
harmful solvents when possible and use respirators when we can't.
Depending upon the weather, we can't hold the environmental
conditions within desirable tolerances, but generally this is of
short duration.

Marc Williams, President
American Conservation Consortium, Ltd.
85 North Road
Fremont, NH 03044 USA


                                  ***
                  Conservation DistList Instance 15:15
                 Distributed: Wednesday, August 8, 2001
                       Message Id: cdl-15-15-002
                                  ***