Baffle System for Fume Hood

U.S. Pat. Nos. 3,218,953 and 3,747,504 describe laboratory fume hoods with a rear particle wall and adjustable baffle adjacent this wall for directing gases from various locations in the fume hood to an upper exhaust port. The baffles described in these patents include an upper baffle with an obtuse angular bend at it center and a lower flat panel baffle. The upper panel is pivotally mounted to the rear wall at an apex of its obtuse angle, and the lower flat panel baffle is pivoted at its bottom end. By pivotally adjusting the two panel baffle system described in these patents, the fume hood can accomodate different weight fumes, i.e. gases. Three separate settings of these baffles handle fumes that are (1) approximately equivalent to air weight, (2) heavier than air, and (3) lighter than air. A schematic illustration of the various settings of the baffles of the above two patents is submitted with the prior art material for background.

U.S. Pat. No. 3,217,630 describes a single panel baffle of obtuse angular design for use with counter top fume hoods. U.S. Pat. No. 2,627,220 illustrates in FIG. 4 a two panel vent spaced immediately above a triangularly shaped deflector. The bottom edge of such deflector is joined to a rear wall of the fume hood and has merely to deflect gas away from the rear wall rather than toward the rear wall.

All of the above two panel baffle systems have a vent above which is mounted a fan that forces the fumes through a conduit to an area outside the building. In a walk-in-hood, the exhaust vent might be 7 feet or more above the floor. The problem is less critical in a counter top fume hood where the vertical rear wall gas suction passage is approximately 3-4 feet in length. However, even in a counter top hood there is some loss of gas sweeping action because of the length of this vertical suction passage. It is important to sweep a very large volume of fumes from all areas of the hood with as small a blower as possible. The reason for this is that extremely large blowers in the exhaust would generate such a tremendous air velocity in the fume hood that experiments within the hood could be hampered. In addition, as the blower size increases, the noise of the motor to power it generally increases.

The present invention overcomes the problem of the prior two panel baffle systems in poor gas flow volumes adjacent the fume hood floor because of the length of vertical draw along the fume hood's rear wall. This invention provides a three panel baffle system with a lower baffle, an intermediate baffle, and an upper baffle spaced apart from each other for gas flow between these baffles, and the lower baffle has a bottom edge around which is a bottom inlet to a draw or chimney passage adjacent the hood's rear walls. Preferably, the lower baffle or the combined lower and intermediate baffle are arranged relative to the rear wall to form an inverted funnel configuration with this rear wall. The separated three panel baffle system provides a more uniform and controllable flow of gases from various portions of the fume hood, with a substantially greater gas sweeping action adjacent the fume hood's floor while using the same gas blowers as previously used with two panel baffle systems.

FIG. 1 shows a sectional view of an interior of a walk-in fume hood showing the relationship of the three baffles;

FIG. 2 is an enlarged view of the lower baffles region of the fume hood of FIG. 1 showing such lower baffle fixed to a rear wall of the fume hood; and

FIG. 3 is a view similar to FIG. 2, but showing an alternate pivoted lower baffle construction.

In FIG. 1, a fume hood includes a housing with a rear wall 1 joined to a top wall 2 that has an exhaust port 3. This exhaust port 3 would be connected to exhaust duct work with an exhaust blower which would pull gases out of the fume hood and force them along the duct work to an outside of the building. Since the blower and duct work are conventional, they do not form part of this invention, and have not been shown.

An inlet port 4 can be connected to duct work from outside the building to draw in outside air so undue amounts of heated room air are not sucked out through the fume hood to the exhaust duct work. This inlet port 4 is connected to a housing 5 which extends along a forward portion of the hood and distributes the inlet air. This inlet air can exit through a series of pivotal flaps shown schematically at 6. A deflector 7 can direct incoming air to an interior portion of the fume hood. Horizontally sliding doors 8 can open and close a front walk-in area of the hood. In FIG. 1, these doors can be considered to be in open position so the fume hood can draw in air from both the room and housing 5 with periodic flexures of flap 6.

In the walk-in fume hood of FIG. 1, blower 9 could be the floor of the room in which the fume hood was installed. Alternately, this floor could be a counter top upon which a shorter fume hood of 3-4 feet height were mounted.

The three panel baffle system includes a lower independently adjustable baffle 10, an intermediate independently adjustable baffle 11, and an independly adjustable upper baffle 12. These three baffles are spaced apart to provide gas inlets at 13, 14, 15, and 16 for collecting fumes from various heights in the fume hood. In the particular experiment conducted in the hood, different fumes could be given off, some which being lighter than air flow upwardly in the fume hood, and others being heavier than air flow downwardly. Thus, it is important to have a fume hood that is highly functional for the particular fumes in the hood. For very light fumes, upper baffle 12 would be tilted to provide a gap at 15 to collect such fumes.

In normal fume hood operation where fumes are composed of gases approximately the same weight as air, or where the fumes are substantially heavier than air, it is extremely important to have a very high volume sweeping action adjacent the floor of the fume hood. For this, a bottom inlet gap 16 is provided at a bottom end of lower baffle 10. This bottom end is preferably 1 to 3 inches above the floor 9. Preferably this vertical bottom gap is substantially greater than a horizontal pinch gap with the rear wall 1, such as at the upper end of baffle 10 or 11.

The bottom end of lower baffle 10 is spaced a greater distance from the rear wall 1 than is its upper end. The intermediate baffle 11 is shown with a lower end adjacent the lower baffle's upper end. The intermediate baffle 11 also upwardly converges toward the fume hood's back wall, as does the lower baffle. Thus, lower baffle 10 and intermediate baffle 11 combine to form with the back wall an inverted funnel configuration. If desired, such funnel configuration could be formed only with the lower panel.

In FIG. 2, a lower panel 20 is shown fixedly secured to a back wall 1 of the panel by supports 17 and 18 which form insignificant obstruction to gas flow. In FIG. 3, a pivotal lower panel 21 is shown in an alternate version. Here a bottom end of lower panel 21 is pivotally mounted in a notch of a support 22 on a back wall 1 of a fume hood. One or more spacer lugs 23 can be provided at an upper end of lower baffle 21 to always insure a gas passage between lower baffle 21 and rear wall 1. For the improved sweeping action adjacent the floor, it is important the upper end of lower baffle 21 does not shut off against the rear wall 1.

The baffle system of this invention could be applied to either standard hoods or auxiliary hoods to control gas flow.

In the foregoing description, specific examples have been used to describe the invention. However, it is understood by those skilled in the art that certain modifications can be made to these examples without departing from the spirit and scope of the invention.