Valve for differential pressure control comprising: - a body extending along a longitudinal axis placed in a fluid flow line at a first pressure, - a sleeve extending from the body, - an actuator member connected to said sleeve, wherein the actuator member comprises a shutter that can move downwards against preloaded elastic means, said shutter being integral to a membrane, said membrane having an upper surface upon which a fluid acts at a second pressure greater than said first pressure, wherein the membrane is enclosed in a shell and is connected to a stem which terminates on the lower part with said shutter, wherein the shell defines a lower chamber therein, placed below the membrane, and an upper chamber, placed above the membrane, the two chambers (16a, 16b) being sealingly isolated from each other, wherein the upper chamber is in flow communication with said fluid at said second pressure, characterized in that the preloaded elastic means comprise: - an outer spring having a lower end which rests on a surface placed on the shell, and - an inner spring, arranged coaxially with respect to the outer spring, whose lower end rests on the surface of the shell, wherein said inner spring can act individually according to a first operating mode or in parallel with said outer spring according to a second operating mode, wherein said first and second operating mode can be selected, and further characterised in that the valve further comprises an adjustment member which comprises: - a threaded rod constrained to the stem and fixed in rotation; - an outer rotatable element having a substantially cylindrical and threaded outer surface; - an adjustment knob constrained in rotation to the outer rotatable element; - a first pusher element for said outer spring, positioned so as to rest on the upper end of the outer spring; - a second pusher element for said inner spring, arranged coaxially with the first pusher element and positioned so as to rest on the upper end of the inner spring; - a selection member adapted to select between a preload condition of the inner spring only or of both the inner and outer spring, and wherein the second pusher element has a longitudinal hole adapted to accomodate the threaded rod, and the selection member comprises a nut, wherein the nut has an inner thread so as to be screwed onto the threaded rod. - a body extending along a longitudinal axis placed in a fluid flow line at a first pressure, - a sleeve extending from the body, - an actuator member connected to said sleeve, wherein the actuator member comprises a shutter that can move downwards against preloaded elastic means, said shutter being integral to a membrane, - an outer spring having a lower end which rests on a surface placed on the shell, and - an inner spring, arranged coaxially with respect to the outer spring, whose lower end rests on the surface of the shell, wherein said inner spring can act individually according to a first operating mode or in parallel with said outer spring according to a second operating mode, wherein said first and second operating mode can be selected, - a threaded rod constrained to the stem and fixed in rotation; - an outer rotatable element having a substantially cylindrical and threaded outer surface; - an adjustment knob constrained in rotation to the outer rotatable element; - a first pusher element for said outer spring, positioned so as to rest on the upper end of the outer spring; - a second pusher element for said inner spring, arranged coaxially with the first pusher element and positioned so as to rest on the upper end of the inner spring; - a selection member adapted to select between a preload condition of the inner spring only or of both the inner and outer spring,