the upper ring 2 is provided with a port 30 for the admission of compressed air this communicates through drilled holes 32 34 36 with the cylindrical chamber 26 the insert 39 s inner wall 27 is of lesser diameter than the adjacent wall 29 of the central hole through the upper ring 2 and the insert provides a curved wall portion 38 leading from the aperture 28 to the wall 27 when compressed air is delivered into the port 30 it flows down into the annular chamber 26 and escapes through the narrow aperture 28 it then follows the smoothly curved surface of the insert 39 s wall portion 38 it entrains additional air and the result is that atmospheric air from generally above the spray head is sucked down through the central passage 7 and blown out at the bottom the air stream blown out in this way is of considerably greater volume than the quantity of compressed air introduced via the port 30 for use the spray head is connected to equipment as described in my u s pat no 4 409 010 the disclosure of which is incorporated herein by reference this equipment will when required supply pressurised air through a flexible hose to the port 30 while also supplying the liquid lubricant through another hose to the port 8 the compressed air causes the.