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Comparing technologies

Time/pressure dispensers: The basic time-pressure syringe (Fig. 3a) is probably the oldest dispensing method. Operation is very simple: The syringe holds the material, and air or a plunger applies pressure to the material to push it through the tip. The higher the pressure and the longer it is applied, the greater the quantity dispensed. It is an open technology because material is always present to the dispensing tip. The only thing keeping the material from continuously' running out of the tip is the shear resistance of the material, combined with the lack of air pressure.

These valves are typically very low cost. They are popular because they may be used with a variety of materials and they are economical because they can be discarded after use. Syringes are best used for dispensing homogeneous materials in manual applications, although the valve is adaptable for attachment to automated equipment (Fig. 4).

The syringe valve dispenses in patterns of fills, beads and dots and works best with materials of medium viscosity. It lacks the precision and repeatability offered by other dispensers, and volumetric accuracy is not one of its key features. However, for dispensing homogeneous materials in non-critical patterns, it does an adequate job.

Fig. 3. Dispensing Technology

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