Which type of filter elements are made of closely woven fabric or treated paper?

The correct answer is that surface filter elements are made of closely woven fabric or treated paper. Surface filters operate by capturing particles on the surface of the filter medium, rather than allowing them to penetrate through the material. The closely woven fabric or treated paper used in these filters provides a fine mesh that efficiently traps larger particles while allowing fluids or gases to pass through.

This design makes surface filters particularly effective for applications where a clear separation of contaminants is required, such as in gas turbine systems where maintaining clean airflow is essential for optimal performance. The choice of materials like fabric or treated paper is significant, as they provide the necessary strength, flexibility, and filtration efficiency to capture debris without excessive pressure drop.

Other types of filters, such as depth filters, work by capturing particles throughout the thickness of the filter material, which is typically more porous and allows for deeper penetration of particulates. Edge filters focus on trapping contaminants at specific edges or points within the flow path, while coarse filters are designed to catch larger particles and are less efficient for finer filtration. Thus, surface filters, characterized by their use of fabric or treated paper, stand out for their effectiveness in specific applications that require stringent filtration standards.