Also known as Gauge Pressure
Overpressure, is any pressure above standard atmospheric pressure (760 Torr or 1013.25 mbar). Vacuum pumps are generally not designed to cope with overpressure at the inlet of the pump. They deal with pressures at atmospheric pressure or below. Some limits as to the overpressure tolerated for a short time can be found in the manual for the pump. Rarely, some vacuum pumps can produce an overpressure as well as vacuum, such as the CLAWVAC OP series. "Gauge pressure" is a term used to define a pressure above atmosphere, where atmospheric pressure is assigned a value of zero.