<p>The invention relates to an electrically activated two-way throttle valve. The opening stroke of the valve piston is determined by an electrical desired value. To control the valve a circuit is provided to obtain a predetermined flow relation in response to the valve member position. According to the invention the pressure difference prevailing at the valve is measured. The pressure differential signal is exponentiated with an exponent. The product of this exponential function and of an input signal defines the desired value for the valve member position. By selecting different values for the exponent, the volume of flow in response to the valve member position is adjusted to an optimum and still further a variety of valve functions may be obtained to operate the valve as flow controlled or pressure controlled for example.</p>
