The spool valve is best used for dispensing lines of material and fills. It is not accurate in dispensing material dots. It excels in dispensing homogeneous materials of medium to high viscosity One area where it is quite effective is dispensing room temperature vulcanizing fluids. It is also used for gasketing and sealing applications, or wherever bulk dispensing is required. In most cases, the needle sits inside the tip.
Material is dispensed by lifting the needle out of the tip, or valve seat.
The farther the needle pulls back from the tip, the longer the needle is held out of the tip, and the higher the pressure applied to the material, the greater the quantity of material dispensed. It handles the dispensing of lubricants and oils far better than the previously mentioned technologies, and often is used for medium-precision patterns and fills in applications such as gasketing and sealing. An auger screw controls the material flow through the dispensing tip. Air pressurizes a syringe that feeds material to a motorized auger screw which rotates and forces the material from the dispensing tip. However, the accuracy of any specific valve model is dependent on the precision of its construction.