least two shutoff valves for blocking a respective flow path application_number US 201715610715 A description fig1 is a schematic representation of a pressure monitoring apparatus 1 known from the prior art the illustrated pressure monitoring apparatus 1 can be used to monitor the pressure in a membrane compressor 2 with an oil side a and a gas side b separated by a membrane for this purpose there is a pressure transducer 3 which measures the pressure in the volume 4 on the oil side a of the membrane compressor 2 between the volume 4 and the pressure transducer 3 there are a nonreturn valve 5 and a shutoff valve 6 in the flow path 7 from the volume 4 to the pressure transducer 3 downstream of the shutoff valve 6 in the direction toward the pressure transducer 3 is a branch 8 in which there is another shutoff valve 9 the nonreturn valve 5 blocks flow in the direction from the pressure transducer 3 to the volume 4 i e the nonreturn valve 5 opens in the direction from the volume 4 to the pressure transducer 3 as long as the pressure in the volume 4 is greater than the pressure in the flow path 7 downstream of the nonreturn valve 5 a medium which is flowing through.