through the supply shut off valve to the paint spray gun 10 is minimized the positioning of the valve shown in fig3 is that position in which the operator would maintain the supply shut off valve 14 in order to operate his paint spray gun 10 turning now to fig4 which represents the configuration of supply shut off valve 14 when the valve is in the shut off position in the cross sectional view represented in fig4 again the positioning of the valve internal 16 relative to the valve body 18 and also relative to the orientation of inlet port 20 and outlet port 22 shows that flow through aperture 30 cannot occur however flow is achieved from inlet port 20 through diverting port 32 which in the configuration shown in fig4 diverts the inlet air or gas to the atmosphere the sizing of diverting port 32 is very critical indeed diverting port 32 is specifically sized and designed to have the same gas or air capacity as the paint spray gun 10 and additionally to have the same pressure drop as the paint spray gun 10 thereby simulating the existence of the paint spray gun 10 even when the air supply to that gun has been interrupted by the supply shut off valve 14 in operation in a multiple user system such as that shown in fig1 supply shut off valve 14 functions to prevent a pressure.