a separate nozzle member which may be discarded or reconditioned the check valves thus prevent one product constituent from leaking across the nozzle and into the companion product constituent passage and plugging up the gun 14a as might otherwise be experienced upon loss of pressure in one constituent line only or a change in the evenness of the trigger pull for example thus while it is not possible to inspect the gun system visually the described check valve arrangement confines problems arising from parts failure and resulting in constituent interaction to the nozzle which can be removed for trouble shooting purposes the check valve arrangement to be described also allows different pressures to be used on the various product constituent lines while maintaining a preselected stoichiometric ratio of the constituents themselves viscosity variables in the product constituents may also be accommodated by proper design of the check valves of the invention referring particularly to fig7 and with secondary reference to fig8 and 9 the nozzle 70a is constructed to include a helically configurated static mixing member 71a disposed in the mixing chamber 138 spaced flowpathwise downstream from a pair of tubulations 140 the tubulations 140 are intended to fittingly engage the bores 78a and 79a and are for this purpose provided with a plurality of annular sealing ribs 142 best seen in fig9 each of the.