A pressure gauge isolator employs a tube or line between the pressure gauge and a source of pressure. A translatable piston or plug is disposed within the line between two constrictions. The first constriction prevents the plug from entering the system which comprises the source of pressure. The second constriction prevents the plug from passing beyond the constriction to prevent excessive pressurization of the gauge and to positively prevent the fluid of the pressure source from reaching the gauge. The plug or piston has a first end in sealing engagement with the inner wall of the tube and facing the pressure source. A second end of the plug has a diameter to provide a slight clearance between it and the inner wall of the tube. The plug is made of resilient material such as rubber.