When a duplex housing pays for itself
A duplex housing costs roughly four times a simplex. On a line where a filter change means a shutdown, it pays for itself in about two changes.
A simplex housing and a duplex housing do the same filtration. The difference is that the duplex has two chambers and a transfer valve, so an element can be changed with the system running.
The arithmetic is simple enough to do on a napkin. Take the cost of the shutdown, multiply by the number of changes a year, and compare it to the difference in housing price. On a press line the answer is usually obvious.