Valve insert for a compact radiator, having a valve insert housing, wherein the valve insert housing comprises a first housing section, a second housing section attached to the first housing section and a third housing section attached to the second housing section, all housing sections (11a, 11b, 11c) being axially aligned, wherein the valve insert housing provides an inlet for a fluid, an outlet for the fluid, and a valve insert seat, a valve insert stem carrying a valve insert plunger, wherein the valve insert plunger acts together with the valve insert seat provided by the valve insert housing in such a way that the relative position between the valve insert plunger and the valve insert seat defines a nominal flow rate through the valve insert from the inlet towards the outlet, a maximum flow pre-setting unit for pre-setting a maximum flow through the valve insert, a pressure difference control unit to keep the flow rate through the valve insert constant or almost constant at the nominal flow rate, wherein the inlet for a fluid, the outlet for the fluid, and the valve insert seat are provided by the first housing section, the maximum flow pre-setting unit has a rotatable pre-setting dial and a pre-setting plunger being linear displaceable when the pre-setting dial becomes rotated, the valve insert stem extends through the pre-setting dial and the pre-setting plunger of the maximum flow pre-setting unit, the valve insert plunger is partially accommodated within the pre-setting plunger and is linear displaceable relative to the pre-setting plunger by actuating the valve insert stem, characterized in that the pressure difference control unit comprises a control diaphragm having an inner folded section and an outer folded section, the outer folded section is attached to the second housing section and the third housing section and provides the pressure difference control, the inner folded section is attached to the pre-setting plunger and allows a movement of the pre-setting plunger relative to the outer folded section. wherein the valve insert housing comprises a first housing section, a second housing section attached to the first housing section and a third housing section attached to the second housing section, all housing sections (11a, 11b, 11c) being axially aligned, wherein the valve insert housing provides an inlet for a fluid, an outlet for the fluid, and a valve insert seat, the inlet for a fluid, the outlet for the fluid, and the valve insert seat are provided by the first housing section, the maximum flow pre-setting unit has a rotatable pre-setting dial and a pre-setting plunger being linear displaceable when the pre-setting dial becomes rotated, the valve insert stem extends through the pre-setting dial and the pre-setting plunger of the maximum flow pre-setting unit, the valve insert plunger is partially accommodated within the pre-setting plunger and is linear displaceable relative to the pre-setting plunger by actuating the valve insert stem, the pressure difference control unit comprises a control diaphragm having an inner folded section and an outer folded section, the outer folded section is attached to the second housing section and the third housing section and provides the pressure difference control, the inner folded section is attached to the pre-setting plunger and allows a movement of the pre-setting plunger relative to the outer folded section.