Maretron's Vacuum Switch detects when a vacuum goes over 7" Hg (3.4 PSI or 0.237 bar). When connected to a fuel supply, this corresponds to the excess vacuum required when filters are clogged.
WARNING: This product can expose you to chemicals including NICKEL (METALLIC) which is known to the State of California to cause cancer. For more information go to P65Warnings.ca.gov.
Owner's Manual (pdf)