Ventilation – Workstation ventilator – Covered workbench chamber
Reexamination Certificate
2000-08-28
2001-10-30
Lu, Jiping (Department: 3749)
Ventilation
Workstation ventilator
Covered workbench chamber
C454S056000
Reexamination Certificate
active
06309294
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vent system for a safety enclosure. More particularly this invention concerns a vent for a lab hood having an openable access door.
BACKGROUND OF THE INVENTION
A standard lab hood is an enclosure one side of which can be opened by means of a movable door, typically an upwardly slidable glass panel. The top of the hood is connected via a branch duct to a main vent duct that is normally continuously evacuated by a vent fan. The branch duct is provided with a shutter that can be moved from a position completely blocking air flow up the branch duct to a position exposing virtually the entire flow cross section of the branch duct for maximum flow. The main duct is maintained continuously under a predetermined subatmospheric pressure.
In order to avoid running the exhaust system at a given hood it is known to mechanically couple the door of the hood to the respective shutter so that, as the door is closed the shutter is closed and vice versa. This ensures that when the door is open there will be sufficient suction to prevent any escape of gases from the hood. When, however, the door is closed there will be little venting and, therefore, little waste of heated or cooled room air and of energy running the suction source. The suction control can be gradual, controlled by a pontentiometer or the like operated as the door is raised and lowered, or two-stage, controlled by end switches operated by the door. At best such systems approximate ideal circumstances.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved vent system for a safety enclosure such as a lab hood.
Another object is the provision of such an improved vent system for a safety enclosure such as a lab hood which overcomes the above-given disadvantages, that is which accurately and sensitively controls venting of the hood.
SUMMARY OF THE INVENTION
A generally closed lab hood having an opening closable by a movable door and connected to a variable-throughput suction source has a vent-control system having according to the invention a sensor for detecting a velocity of flow of air into the hood and for generating an output corresponding to the detected velocity. A controller connected to the sensor and to the variable-throughput suction source receives the output and operates the suction source to set throughput of the source at a level corresponding to the output so that as the detected velocity increases the throughput of the suction source is increased and vice versa.
Thus with this system the only really critical factor—air flow from the outside into the hood—is directly monitored and the suction source is controlled to keep this flow at a desired level. No matter what is going on, there will be a certain air flow into the hood. Thus in a situation where the hood is closed but a reaction inside the hood is generating massive amounts of gas, the suction will be set high, unlike the prior-art systems which set the suction rate purely in response to door position so that under these circumstances the suction rate would be very low.
The controller includes a sensor tube having an inner end opening into the hood and an outer end opening outside the hood and means in the sensor tube for detecting the velocity of air-flow therethrough. This tube is mounted at a distance from the opening. It can be a small-diameter tube extending through the roof of the hood so that this system can easily be retrofitted to existing equipment.
In addition according to the invention the controller operates proportionally to set the throughput of the suction source relative to the air-flow velocity. Thus there is a direct relationship between suction-source throughput and detected air-flow velocity.
The suction source includes a stepless actuator capable of steplessly varying throughput of the source and connected to the controller. The source has an intake duct and a shutter pivotal in the duct to vary a flow cross section of the duct. The actuator has a link including a spring connected to the shutter. This spring gives a damping effect so that a sudden pressure change will not create an instantaneous response that could be incorrect.
REFERENCES:
patent: 5304093 (1994-04-01), Sharp et al.
patent: 5415583 (1995-05-01), Brandt, Jr.
patent: 5518446 (1996-05-01), Jacob
Baumeister Gregor
Sadkowski Manfred
Sefker Thomas
Wedler Sven
Dubno Herbert
Gebruder Trox Gesellschaft mit beschrankter Haftung
Lu Jiping
Wilford Andrew
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