Dear User,
The number of filters depends upon the type of filtration. In case of separating a mixture of components wit varying size of particles we can use more number of filters with progressively smaller size i.e. filter with the largest pore first and the filter with smallest pore at the last so that the components get separated according to their size.
If a solution with single component or o different component of similar size is to be filered, than a single filter of appropriate size should be used.