NEGATIVE PRESSURE, RE-CIRCULATING

1. Negative Pressure: This method is similar to the push-pull in that it re-circulates all the air back into the work area. The major difference is that the air flow is generated entirely by the air being pulled into the collector with no assistance from the collector exhaust. This system is used when a small enclosure can be erected inside the work area. The air flow generated need only be calculated for the opening of the CCB, not the entire work area. As the collector pulls air through the open side of the CCB it creates a negative pressure within the CCB, eliminating the possibility of any dust escaping the open front of the enclosure. This is true even when a compressed air nozzle may inadvertently be directed toward the opening, thereby blowing dust outside the enclosure. When this happens, the high inflow of air into the enclosure captures this transient dust and pulls it back into the enclosure. The clean air is then exhausted back into the work area where it will eventually circulate around and come through the open front of the CCB once again. This is very cost effective when dealing with a high dust load process or where there is no tolerance for any transient dust escaping the capture zone. In effect, if the work is accomplished inside the enclosure, no matter how high the dust load, there will be zero dust escaping the enclosure. The added advantage to this method is that along with 100% capture, the air volume and thus the fan size required for this system is much smaller than one used for the entire work area. The fact is, however, that besides isolating dust generated inside the enclosure, the entire building air volume is pulled through in due course and so benefits from the filtration. Both of these re-circulating systems have their uses and both can be cost effective if selected correctly. A push-pull system incorrectly applied can be less effective and actually cost more than a negative pressure system due to the in-efficiencies of capturing air within a CCB type enclosure. A negative pressure system, on the other hand, can be entirely in-effective at collecting dust from within a large room due to the lack of air flow control which is needed to direct contaminated air into the filter system. Both have their place and when used correctly both will result in a very cost effective system.

This entry was posted on Friday, April 4th, 2008 at 9:34 pm and is filed under White papers. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.