Which type of filter may only work at its advertised millipore size during installation?

The correct answer is nominal filter. Nominal filters are designed to remove particles up to a certain size, often specified in microns, but their actual performance can vary based on the conditions under which they are used and the specific characteristics of the fluid being filtered. This means that while they have an advertised millipore size, their effectiveness can depend on factors such as flow rate and the nature of the particulates in the fluid.

In contrast, absolute filters are designed to capture 99.9% of particles at their specified size under specified conditions, meaning they consistently perform at their advertised rating. Micron filters, which generally refer to filters that are described by their millipore size, may function similarly to nominal filters, but the term is broader and doesn't necessarily indicate performance reliability to the same extent. Carbon filters are used primarily for removing contaminants like chlorine or organic compounds, rather than being predicated on particle size filtration, which is outside the context of this question.