RE: Fume hood

I discovered an unused basement window (no glass - just the frame) that
had been boarded over on both the inside and the outside. I removed the
inside sheeting.
 
I cut a 6" hole in the outside sheeting. I installed an elbow (pointed
up, since the window is right at ground level), a 3 foot length of
straight pipe, and two 90 degree elbows on top (to point the opening
downward), all 6". This is the pressurized part of the system.
 
>From the inside, in the window space, I inserted the duct fan directly
into the elbow. The fan isn't very long so it doesn't protrude into the
window space very far.
 
I used 2x2 to make a frame the inside the window frame and a cover goes
up against the 2x2 frame to create a vacuum space the size and depth of
the original window.
 
This "cover" (visible on my darkroom page), has four "air valves" (made
from sliding plywood baffles) so I can draw air from a number of
different areas.
 
The whole system was originally build for 4" ducting. When I converted
to 6" to get more air flow, I only had to convert "the pressure side" to
draw a stronger vacuum between the cover and the outside sheeting. The
remaining piece of 4", from the fume chamber to the valve on the cover,
is only about 10" long and doesn't seem to restrict the air flow too
badly.
 
Since I had already built the cover with four 4" air valves, I didn't
want to have to rebuild it for 6" unless I had to. As it turned out, I
didn't have to start all over again and build new valves :-)
 
Dianne
 
 
-----Original Message-----
From: Michael Koch-Schulte [mailto:mkochsch@shaw.ca]
Sent: Monday, October 31, 2005 9:48 AM
To: alt-photo-process-l@sask.usask.ca
Subject: Re: Fume hood

        So, the 6" pipe (let's call it the vacuum run) is drawing from
inside or outside the house? If inside, do you need to provide make up
air? I'm wondering if there is the potential for backdraft? The 4" joins
the 6" how? using a reducer and a Y-connector or a T-connector? Thx.
         
        ~m
Received on Mon Oct 31 12:24:00 2005