Abstract: A plural component dispensing system includes supplies which furnish first and second components, such as a resin and catalyst, under pressure to a hand-held dispensing device having first and second valves, respectively. First and second passageways lead from the first and second valves to a mixing chamber in which the components are mixed, and from which the components are ejected. Upon mixing, the components are subject to increasing viscosity and hardening. A third valve controls flow of a purging medium from a supply of such a medium to the mixing chamber. A sensing device, such as a pressure sensor, senses the orientation of either/or both of the first and second valves. When the first and second valves are moved to positions to halt the flow of the two components, the sensing device generates a signal to start a first timing device.