A spray nozzle, comprising: a nozzle body having a proximal end, a distal end, a first through bore extending between the proximal and distal ends of the nozzle body, and a valve seat disposed at the distal end of the nozzle body, the proximal end of the nozzle body defining a shoulder surface; a valve stem slidably disposed in the first through bore of the nozzle body and including a proximal end, a distal end, and a first valve head, the first valve head defining a seating surface adapted to engage the valve seat when the valve stem is in a closed position and adapted to be spaced away from the valve seat when the valve stem is in an open position; a fluid conduit disposed in the valve stem and defining a fluid outlet in the first valve head at the distal end of the valve stem; and a second valve head attached to the fluid outlet at the valve head of the valve stem, the second valve head defining a nozzle opening that is continuously open in fluid communication with the fluid conduit in the valve stem; and a bias device generating a force biasing the first valve head of the valve stem toward the valve seat of the nozzle body, the bias device comprising a nut attached to the proximal end of the valve stem and a spring disposed between the nut and the proximal end of the nozzle body, wherein the nut comprises a hollow tubular member including a collar portion defining an annular recess to at least partially accommodate the spring, wherein upon application of a first fluid pressure, which is less than a threshold fluid pressure, on the seating surface of the first valve head, the bias device maintains the valve stem in the closed position while the second valve head is continuously open, and upon application of a second fluid pressure, which is at least as great as the threshold fluid pressure, on the seating surface of the first valve head, the valve stem moves from the closed position to the open position while the second valve head remains continuously open, and when the valve stem is in the closed position, the collar portion of the nut is spaced away from the shoulder surface of the proximal end of the nozzle body, and when the valve stem is in the open position, the collar portion of the nut is in contact with the shoulder surface of the proximal end of the nozzle body. a nozzle body having a proximal end, a distal end, a first through bore extending between the proximal and distal ends of the nozzle body, and a valve seat disposed at the distal end of the nozzle body, the proximal end of the nozzle body defining a shoulder surface; a valve stem slidably disposed in the first through bore of the nozzle body and including a proximal end, a distal end, and a first valve head, the first valve head defining a seating surface adapted to engage the valve seat when the valve stem is in a closed position and adapted to be spaced away from the valve seat when the valve stem is in an open position; a fluid conduit disposed in the valve stem and defining a fluid outlet in the first valve head at the distal end of the valve stem; and a second valve head attached to the fluid outlet at the valve head of the valve stem, the second valve head defining a nozzle opening that is continuously open in fluid communication with the fluid conduit in the valve stem; and a bias device generating a force biasing the first valve head of the valve stem toward the valve seat of the nozzle body, the bias device comprising a nut attached to the proximal end of the valve stem and a spring disposed between the nut and the proximal end of the nozzle body, wherein the nut comprises a hollow tubular member including a collar portion defining an annular recess to at least partially accommodate the spring, wherein upon application of a first fluid pressure, which is less than a threshold fluid pressure, on the seating surface of the first valve head, the bias device maintains the valve stem in the closed position while the second valve head is continuously open, and upon application of a second fluid pressure, which is at least as great as the threshold fluid pressure, on the seating surface of the first valve head, the valve stem moves from the closed position to the open position while the second valve head remains continuously open, and when the valve stem is in the closed position, the collar portion of the nut is spaced away from the shoulder surface of the proximal end of the nozzle body, and when the valve stem is in the open position, the collar portion of the nut is in contact with the shoulder surface of the proximal end of the nozzle body.