A valve for on/off and/or control applications, comprising: - a housing having an inlet port and an outlet port; - a supply passage extending between the inlet port and the outlet port; - a supply valve core provided in the supply passage and operable between closed and open positions; - an operating member for moving the supply valve core between its closed and open positions; - a set screw that is screwable in an axial direction into and out of a complementary female threaded opening in a valve part for changing a setting of the valve, in which the set screw comprises a free outer end that projects outside the valve part, in which the set screw comprises a gripping part on its free outer end for a tool to be engageable thereupon, and in which the free outer end of the set screw comprises a male thread onto which a locking nut is screwed for a primary locking of the set screw relative to the valve part, characterized in that, a protective cap is provided that covers the free outer end of the set screw, wherein the cap comprises a first cap portion with a rotation space that is designed to fit freely rotatable over the locking nut, and wherein the cap comprises a second cap portion with a complementary female thread that is screwed onto the male thread on the free outer end of the set screw towards a locked position for a secondary locking of the set screw relative to the valve part, wherein the cap is provided with a circumferential wall and a front wall for together with the valve part enclosing the locking nut, the male thread and the gripping part on the free outer end of the set screw, the second cap portion comprising a bore portion with said female thread, which bore portion is blind towards said front wall of the cap, and wherein in said double locked position: • a back circumferential edge of the cap has come to lie against the housing; or • an inner end wall of the cap, that delimits the rotation space towards the side of the front wall, has come to lie against a front face of the locking nut. - a housing having an inlet port and an outlet port; - a supply passage extending between the inlet port and the outlet port; - a supply valve core provided in the supply passage and operable between closed and open positions; - an operating member for moving the supply valve core between its closed and open positions; - a set screw that is screwable in an axial direction into and out of a complementary female threaded opening in a valve part for changing a setting of the valve, in which the set screw comprises a free outer end that projects outside the valve part, in which the set screw comprises a gripping part on its free outer end for a tool to be engageable thereupon, and in which the free outer end of the set screw comprises a male thread onto which a locking nut is screwed for a primary locking of the set screw relative to the valve part, in which the set screw comprises a free outer end that projects outside the valve part, in which the set screw comprises a gripping part on its free outer end for a tool to be engageable thereupon, and in which the free outer end of the set screw comprises a male thread onto which a locking nut is screwed for a primary locking of the set screw relative to the valve part, wherein the cap comprises a first cap portion with a rotation space that is designed to fit freely rotatable over the locking nut, and wherein the cap comprises a second cap portion with a complementary female thread that is screwed onto the male thread on the free outer end of the set screw towards a locked position for a secondary locking of the set screw relative to the valve part, wherein the cap is provided with a circumferential wall and a front wall for together with the valve part enclosing the locking nut, the male thread and the gripping part on the free outer end of the set screw, the second cap portion comprising a bore portion with said female thread, which bore portion is blind towards said front wall of the cap, and wherein in said double locked position: • a back circumferential edge of the cap has come to lie against the housing; or • an inner end wall of the cap, that delimits the rotation space towards the side of the front wall, has come to lie against a front face of the locking nut. • a back circumferential edge of the cap has come to lie against the housing; or • an inner end wall of the cap, that delimits the rotation space towards the side of the front wall, has come to lie against a front face of the locking nut.