A device for regulating the flow in a heating and cooling system. The flow is controlled by a complete valve realized as a combination of a difference pressure valve (5) and a flow controlling valve (6) where the complete valve construction allows flushing of the tube system where the valve is mounted. A first static pressure (P1) in the inlet (2), a second static pressure (P2) in the intermediate chamber (4) and a third static pressure (P3) in the outlet (3) are measured by the measuring nipples (27a, 27b) and the difference between the second and the third static pressures (P2, P3) is adjustable during operation.