Valves are selected by fluid viscosity, fluid content and the purpose that the valve will be used for. Spool valves are for high viscosity materials. Poppet valves perform smaller shots sizes. Diaphragm valves are for volatile fluids and UV resins. Pinch-tube valves handle volatiles and cyanoacrylates. Needle valves are for dots and auger valves are for high viscosity fluids such as solder paste applications.