Fume hood

A compact fume hood arrangement includes a bypass channel mounted to a top panel of the fume hood which effectively extends a front open face of the fume hood upwardly providing an air path through the bypass channel which provides sufficient air flow to prevent disadvantageous air currents due to excessive face velocity. A vertical sash can be used such that raising of the sash proportionally closes the bypass channel while opening the open face of the fume hood.

BACKGROUND OF THE INVENTION 
The present invention relates to laboratory fume hoods. Particularly, the 
invention relates to fume hoods having air flow arrangement for sweeping 
the interior area of the fume hood when the front sash is in an open or a 
closed orientation. 
The basic concept behind hood design is to protect the user. The hood 
should provide sufficient air flow across the face/opening to protect the 
user from harmful fumes given off by experiments within the hood. However, 
if the velocity of air entering the hood is too high, extremely turbulent 
air patterns inside the hood could compromise the hood's containment 
putting the user in danger. The efficiency of the hood is also adversely 
affected if too much air is being exhausted. 
A bypass area provides a means to control the velocity of the air across 
the face of the hood throughout the range of motion for the sash. 
Typically, a fume hood provides a vertically positionable sash liftable to 
allow a laboratory worker to move his hands within the hood to manipulate 
his samples. When, however, the sash is closed, air must be provided to 
pass through the hood to sweep the hood of generated gases or other 
undesired volatile materials. Typically, the bypass is located between the 
front of the hood, the area in front of the sash glass. This bypass 
provides air to the interior of the hood while the sash is in the closed 
position. However, this space must be sufficient to provide enough air to 
prevent extremely high velocity air from entering the hood when the sash 
is only open a small amount. These high velocities may cause adverse air 
patterns inside the hood. Since this bypass area is typically located in 
front of the sash, the working space within the hood is compromised. Such 
fume hoods are disclosed in, for example, U.S. Pat Nos. 3,318,227, 
4,142,458 and 4,377,969. 
Alternatively, fume hoods can have horizontally reciprocal sashes such as 
disclosed in U.S. Pat. No. 4,023,473 or combination vertical and 
horizontal sash, such as described in U.S. Pat. No. 4,142,458. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a fume hood which is 
compact in size and arrangement. It is an object of the present invention 
to provide a fume hood which provides sufficient sweeping air during a 
period when the front sash is closed and also when the front sash is 
opened during manipulation inside the hood by the laboratory technician. 
It is an object of the present invention to provide sufficient bypass air 
flow area to provide enough air to prevent extremely high velocity air 
from entering the hood when the sash is opened only a small amount. 
It is an object of the invention to provide a fume hood cabinet which 
maximizes the working area for a particular size cabinet. 
The object of the present invention is achieved by a fume hood provided in 
the form of a cabinet having a front sash pane liftable for access by a 
laboratory technician into the cabinet of the fume hood. A bypass is 
provided for air to pass into the fume hood when the pane is closed. This 
bypass is located behind the sash. As the sash is opened by raising, the 
bypass is closed off proportionately, forcing more air to be supplied 
through the opened front of the hood. The arrangement provides a means of 
controlling the velocity of the air entering the hood while providing the 
necessary containment to protect the laboratory technician. 
Alternately, a bypass can be provided behind the sash for fume hoods having 
horizontally reciprocal sashes or combination vertical/horizontal operated 
sashes. 
The objects are inventively achieved in that a channeled bypass element is 
mounted on a top level of the hood behind the sash. 
The objects are achieved in that the channeled bypass element is a box 
shaped elongate channel with an open front face and an open bottom face. 
The hood provides a cabinet with a top wall, bottom wall and side walls. 
An area is preserved behind the channel for mounting other equipment. The 
elongate channel effectively extends the bypass area of the cabinet behind 
the sash resulting overall in a compact design.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 discloses a fume hood 10 of the present invention. The fume hood 10 
is a cabinet structure having a top panel 12, cover side panels 14, 16 and 
a bottom panel 18. A back panel 22 and a front sash 24 and inside walls 
19, 20 are provided to form a substantially closed working area. A baffle 
80 (shown in FIG. 7) is not shown in FIG. 1, for clarity. An air outlet 26 
through the top wall 12 allows for fan suction of air through and out of 
the fume hood 10. When the front sash 24 is in a lowered or closed 
position as illustrated in FIG. 1, an open face 30 is left between the top 
of the front sash 24 and the top panel 12. A fixed front panel 34 is 
spaced outwardly and forwardly from a plane defined by the front sash and 
confronts the open face 30. The fixed front panel 34 may also include as 
illustrated in FIG. 1 a glass portion 34a for viewing into the working 
area of the flume hood. An open area or gap 36 lying in a horizontal plane 
is provided between the front panel 34 and the plane defined by the front 
sash 24 for permitting downward passage of air into the working area. The 
sash 24 is guided by conventional means for vertical sliding movement 
between the sidewalls 19 and 20 within the plane of the front sash. 
FIG. 2 shows the sash 24 in its lowest most position. The sash provides a 
bottom frame member 38 which seats onto a deflector vane 40 on the bottom 
wall 18. In this closed configuration, air A blows through the opening 36 
and under the deflector vane 40 inside the cabinet volume V. Regardless of 
sash position air A flows into the cabinet volume V under the deflector 
vane 40 across the work surface 18 keeping the surface clear of fumes. As 
shown in FIG. 2, a bypass channel 44 extends upward from the top panel 12 
and all the way across the width of the fume hood 10. The bypass channel 
has a vertical leg 44a extending upward from the top panel 12 and a 
horizontal leg 44b extending forwardly from the vertical leg 44a. As 
illustrated in FIGS. 2-4, the top panel 12 has a forward edge 12a which is 
rearward of the plane defined by the front sash 24. The horizontal leg 44b 
of the bypass channel 44 extends forward from the vertical leg 44a 
extending to the plane defined by the front sash 24 but lies in a plane 
above a plane defined by the top panel 12. Thus, the bypass channel 44 
creates a bypass area 32 into the working area or cabinet volume V between 
the edge 12a of the top panel 12 and a plane defined by the front sash 24. 
As shown in FIG. 3, when the sash 24 is partly raised such that a top edge 
24a of the sash approaches the plane of the top wall 12, the bypass area 
32 remains open so that air A may pass downwardly through the gap 36 and 
bypass area into the working area or cabinet volume V. When the sash is in 
this partly raised position, air A may also pass through a large window 
opening 48 beneath the bottom edge 38 of the sash 24 created by the 
elevation of the sash with respect to the deflector vane 40. 
FIG. 4 shows the pane 24 fully raised to close off the opening 32 and 
require the air A to proceed through the opening 48 into the fume hood 
volume V. 
FIG. 5 shows the pane 24 having the top member 24a including a frame 
arrangement of pane holding side walls 50a, 50b and angular extending 
deflector 52 which deflects air inwardly into the fume hood volume V. A 
bracket 54 is used to attach the panel 34 to the hood. 
The bypass channel 44 effectively extends the bypass area behind the plane 
of the sash while retaining a "penthouse" area behind the bypass channel 
44 for mounting equipment such as a fan 56 (shown schematically in 
phantom) or light, and cable suspension pulleys including front pulleys 58 
(one shown), back pulleys 60, 62 and a tension adjusting mechanism 66. A 
compact vertical arrangement up to a top extent 70 of the cover side 
panels 14, 16 is provided while at the same time maximizing the working 
area inside the fume hood 10. The bypass channel 44 has a vertical profile 
to fit between the top wall 12 and the top extent 70 of the cover side 
panels 14, 16. 
FIG. 6 and 7 demonstrate an advantage of the present invention. For the 
typical hood of FIG. 6, the depth dimension is D, the bypass dimension is 
B and the work surface dimension, inside the hood is C. A sash 24' closes 
the hood 10'. An internal baffle 80 directs air to the air outlet 26. The 
baffle 80 has appropriate openings 80a, 80b to allow air to flow behind 
the baffle to the air outlet 26. In comparison, the hood 10 shown in FIG. 
7, having the same depth D can be provided with an increased work surface 
dimension W (W&gt;C) by utilizing the smaller bypass dimension X (X&lt;B) in 
conjunction with the added bypass dimension Y. The back panel 22-to-baffle 
80 distance F is assumed to be constant between FIGS. 6 and 7. 
Although the present invention has been described with reference to a 
specific embodiment, those of skill in the art will recognize that changes 
may be made thereto without departing from the scope and spirit of the 
invention as set forth in the appended claims.