Kit to change the nozzle valves mounting to clip on and turn them upright. This consists of several items: clips, clip mountbracket, screws and nuts to hold the clips to the mount. You must use your original valve mount bracket. To use your original valve mount bracket you must drill and tap (thread) 5 holes in it. There are 3 main benefits of this kit. 1) The clips make it easier to change a defective valve. 2) With the valves inverted, if an internal diaphragm develops a leak, the reagent is not inclined to go into the electrical part of the valve. This means that the valve driver board will not be shorted out. 3) You can use the better quality valve that we sell for the 3900 and the Northwest Instruments. The improved valve is PN:603-101634. Does not include the Valve Mount Bracket. You must use your old Valve Mount Bracket. You must drill and tap 5 holes in the old mount to use it. Instructions are included.