The fume cover on the Sub-Surface fillers is intended to remove the fumes
from the container as it fills. It is intended only for use when filling
closed top containers with openings less than 75 mm/3" diameter.
In consists of an inverted "bowl" approximately 125 mm/5" in diameter
(B) with a 25 mm/1" connection for an exhaust hose (E).
The exhaust hose is connected to a vacuum pump to provide a small amount of negative pressure.
When the nozzle is in the container, the cover rests on the top of the container. As air is exhausted from the container, it is drawn into the fume cover and exits through the exhaust hose.
The nozzle will rise slowly, and the drip cup will slide down the nozzle. As it slides down, the gasket inside the drip cup will "wipe" the nozzle tube.
The guides (A) will stop the downward slide of the fume cover. Normally, they are set to stop the downward slide when the fume cover is approximately 200 mm from the tip of the nozzle on a DN-25 filler or 600 mm from the tip on the Drum filler. In this case, the nozzle would rise to its safety stop and be set approximately 25 mm/1" above the top of the container and the end of the fill would be completed.
Alternatively, the stop may be set so that the fume cover will slide close to the tip of the nozzle. In this case, the fume cover will rest on the container until the shut-off and the shut-off weight must be set to compensate for the weight of the fume cover on the drum.
When the nozzle rises, the fume cover will slide down until the setting on the guides (A) stop the descent.
The negative pressure in the fume cover will give a continuous air flow into the fume cover to have an air flow away from the filling nozzle.
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