Bypass fumehood speaks to what is a bypass fumehood and how does bypass fumehood work.
As with all laboratory constant volume bypass fumehoods, this type have fixed vertical airfoils or angled aerodynamic entries on each side.
It also has a fixed horizontal airflow below the sash and above the work surface, and adjustable baffles at the rear to adjust air flow patterns. This will maintain a relatively uniform air velocity through the sash opening regardless of the position of the sash.
These fumehoods are designed and constructed so that at a certain sash position and lower, room air is allowed to enter the fumehood by a route other than through the sash opening. This allows a relatively constant exhaust airflow rate to be exhausted from the fumehood over the operating range of the bypass.
These fumehoods are sometimes called balanced flow fumehoods because the exhaust flow is initially balanced to provide a face velocity through the sash opening at all times at 100 fpm.
While a full open sash height is usually 12” whatever the normal operating position will constitute a single, specific sash opening often in the range of 12” to 18”. This position should be clearly labeled and sash stop provided.
The normal operating position imposes a significant restriction to the user in carrying out procedures within the fumehood, but it is necessary to provide optimum protection of the user from contaminant escape.
Each fumehood is served by it’s own dedicated exhaust fan which may be roof mounted or in an upper mechanical room..