A filter core sample is best collected for solids retention analysis when

A filter core sample is best collected for solids retention analysis when

• A. When the filter media is dry
• B. When the filter media has been drained and the media is still damp
• C. When the water has been drained to just above the media
• D. At any of the above scenarios

Answer: (B)

The key idea is to sample the filter bed in a state that reflects how it retains solids during operation. If the media is completely dry, the solids can detach or crumble when you take the core, leading to an underestimate of what the bed actually holds. If the media is still full of water, the sample includes extra water that isn’t part of the solids retained by the media, which can skew the solids mass. Draining the water and leaving the media still damp provides a stable, cohesive core where the solids remain in place within the pores as they would during normal filtration. This gives a representative measurement of solids retained by the bed, which you can then dry and weigh to determine solids retention accurately.

The key idea is to sample the filter bed in a state that reflects how it retains solids during operation. If the media is completely dry, the solids can detach or crumble when you take the core, leading to an underestimate of what the bed actually holds. If the media is still full of water, the sample includes extra water that isn’t part of the solids retained by the media, which can skew the solids mass. Draining the water and leaving the media still damp provides a stable, cohesive core where the solids remain in place within the pores as they would during normal filtration. This gives a representative measurement of solids retained by the bed, which you can then dry and weigh to determine solids retention accurately.