Slots versus holes in preliminary treatment screening ?
asked 17 December 2015 asked by Amy (2850 points)
Both types of screens can be beneficial. Hole-type screens tend to cost more when it comes to cleaning them up, but that's because they remove more debris. They also tend to have more long-term maintenance costs because many of them have seals which wear down over time and leak on you. On the other hand, slot-type screens tend to have a lower impact on your headloss. Determining which one to use depends on the system itself. If you're using a membrane-based system, for example, you almost have to go with a hole-type screen. Graduated screening before the hole-type screen is often required too to get the results you need for your downstream process. The problem with hole-type screens, in theory, is that larger objects can pass through them. If you are dealing with a high flow rate and there is cylindrical debris being screened out of the flow, without the graduated screening, some of that large debris can get past. Bottom line: there isn't much difference between a 3mm slot-type screen and a 3mm hole-type screen. You'll get maybe 15% better filtering from the hole-type screen, but at a higher cost.