A flow meter for calculating volume flow from pressure measurements, the flow meter comprising: a housing; a tube disposed within the housing, the tube having an inlet portion having a first inner diameter (d 1), an outlet portion having a second inner diameter (d 2), and an intermediate portion having a third inner diameter (d 3) which is smaller than both the first inner diameter (d 1) and the second inner diameter (d 2); a first pressure measuring point located in the inlet portion and adjacent the intermediate portion, a first port being provided at the first pressure measuring point for measuring a first pressure; a second pressure measuring point located in the intermediate portion a second port being provided at the second pressure measuring point for measuring a second pressure; a flow exhaust channel in fluid communication with the outlet portion, the exhaust channel at least partly surrounding the tube; a pilot pressure chamber, delimited by a pilot pressure chamber housing, arranged adjacent to the outlet end of the outlet portion and adjacent to the exhaust channel; a flexible membrane (36,56) provided about the outlet portion of the tube, the flexible membrane (36,56) having a peripheral seal section, a spring suspension system, and a central portion, the peripheral seal section being positioned about a circumference of the outlet portion, and wherein the flexible membrane (36,56) operates as a pressure seal between an interior of the tube and the flow exhaust channel, the flexible membrane (36,56) also separating the pilot pressure chamber from an interior portion of the tube and the flow exhaust channel, wherein when a pressure in the pilot pressure chamber is higher than a pressure in the outlet portion the sea section substantially seals against the circumference of the outlet portion, and when the pressure in the outlet portion is higher than the pressure in the pilot pressure chamber the flexible membrane (36, 56) flexes towards the pilot pressure chamber via a flexing movement, and characterised by a turbulator for creating turbulent flow being provided about the inlet portion of the tube, the turbulator having a cylindrical shape formed by a cylinder wall and a plate, the plate being arranged substantially perpendicular to the intended direction of gas flow upstream of the turbulator, wherein a plurality of apertures are provided therethrough which are configured to allow a quantity of air to pass through the plurality of apertures. a housing; a tube disposed within the housing, the tube having an inlet portion having a first inner diameter (d 1), an outlet portion having a second inner diameter (d 2), and an intermediate portion having a third inner diameter (d 3) which is smaller than both the first inner diameter (d 1) and the second inner diameter (d 2); a first pressure measuring point located in the inlet portion and adjacent the intermediate portion, a first port being provided at the first pressure measuring point for measuring a first pressure; a second pressure measuring point located in the intermediate portion a second port being provided at the second pressure measuring point for measuring a second pressure; a flow exhaust channel in fluid communication with the outlet portion, the exhaust channel at least partly surrounding the tube; a pilot pressure chamber, delimited by a pilot pressure chamber housing, arranged adjacent to the outlet end of the outlet portion and adjacent to the exhaust channel; a flexible membrane (36,56) provided about the outlet portion of the tube, the flexible membrane (36,56) having a peripheral seal section, a spring suspension system, and a central portion, the peripheral seal section being positioned about a circumference of the outlet portion, and wherein the flexible membrane (36,56) operates as a pressure seal between an interior of the tube and the flow exhaust channel, the flexible membrane (36,56) also separating the pilot pressure chamber from an interior portion of the tube and the flow exhaust channel, wherein when a pressure in the pilot pressure chamber is higher than a pressure in the outlet portion the sea section substantially seals against the circumference of the outlet portion, and when the pressure in the outlet portion is higher than the pressure in the pilot pressure chamber the flexible membrane (36, 56) flexes towards the pilot pressure chamber via a flexing movement, and characterised by a turbulator for creating turbulent flow being provided about the inlet portion of the tube, the turbulator having a cylindrical shape formed by a cylinder wall and a plate, the plate being arranged substantially perpendicular to the intended direction of gas flow upstream of the turbulator, wherein a plurality of apertures are provided therethrough which are configured to allow a quantity of air to pass through the plurality of apertures.