Stop valve for hydronic installations, comprising: a valve housing providing a valve inlet, a valve outlet and a valve seat, said valve inlet and valve outlet being connectable into a pipe of the hydronic installation; a valve plunger mounted to a first end of a valve stem and acting together with the valve seat, whereby the stop valve is closed when the valve plunger is in its closed position pressed against the valve seat, and whereby the stop valve is opened when the valve plunger is in its opened position lifted up from the valve seat; a hand wheel mounted to a second end of the valve stem for transferring the valve plunger mounted to the first end of the valve stem between its closed position and its opened position; a flow measurement position of the valve plunger providing a defined pressure drop between the valve inlet and the valve outlet when the valve plunger is in its measurement position, wherein the flow measurement position of the valve plunger is defined by a mechanical stop element (29, 33) limiting the movement of the valve plunger when the same is transferred from its opened position in its closed position by operating the hand wheel; characterized in that the mechanical stop element is provided by a stop element being an integral part of the hand wheel; the mechanical stop element is provided by a push-button of the hand wheel, whereby the push-button provides a mechanical stop in the operated position of the same and whereby the push-button does not provide the mechanical stop in the released position of the same; the push-button is in its operated position bent inwardly with respect to its released position, whereby the push-button acts in its operated position and in the flow measurement position of the valve plunger together with a stop provided by the valve housing or by a valve insert positioned between the valve housing and the valve stem. a valve housing providing a valve inlet, a valve outlet and a valve seat, said valve inlet and valve outlet being connectable into a pipe of the hydronic installation; a valve plunger mounted to a first end of a valve stem and acting together with the valve seat, whereby the stop valve is closed when the valve plunger is in its closed position pressed against the valve seat, and whereby the stop valve is opened when the valve plunger is in its opened position lifted up from the valve seat; a hand wheel mounted to a second end of the valve stem for transferring the valve plunger mounted to the first end of the valve stem between its closed position and its opened position; a flow measurement position of the valve plunger providing a defined pressure drop between the valve inlet and the valve outlet when the valve plunger is in its measurement position, wherein the flow measurement position of the valve plunger is defined by a mechanical stop element (29, 33) limiting the movement of the valve plunger when the same is transferred from its opened position in its closed position by operating the hand wheel; characterized in that the mechanical stop element is provided by a stop element being an integral part of the hand wheel; the mechanical stop element is provided by a push-button of the hand wheel, whereby the push-button provides a mechanical stop in the operated position of the same and whereby the push-button does not provide the mechanical stop in the released position of the same; the push-button is in its operated position bent inwardly with respect to its released position, whereby the push-button acts in its operated position and in the flow measurement position of the valve plunger together with a stop provided by the valve housing or by a valve insert positioned between the valve housing and the valve stem.