An actuator is operatively connected to a closing member via a tappet. The closing member is introduced in a valve chamber and forms, with a conically tapering valve seat as part of a servovalve, a seal resistant to high pressure. The cross section of the closing member is configured to be mushroom-shaped, a closing head being in the form of a part-sphere and having a central flattening, with the result that the tappet has an enlarged bearing surface. A stem of the closing member is surrounded by a valve spring. The closing member is preferably shaped out of a solid sphere.