There are several types of material dispensers available for the manufacturing process. The most common types being positive displacement dispensers and time/pressure dispensers. Both types have their perks, but when it comes to precise dispensing, positive displacement dispensers often take the crown.
Positive displacement covers a wide variety of dispenser types but in general refers to the movement of pressurized material through an enclosed chamber via mechanical means. The movement can come from pistons, gears, or screws. The mechanical nature of positive displacement dispensers allows them to operate at a higher level of precision than a time/pressure dispenser. Choosing a type of positive displacement dispenser is completely dependent on the application. Gear, screw, and peristaltic pumps allow for continuous flow, whereas piston pumps can only dispense a volume as large as the piston but have a higher level of accuracy.
Piston-driven positive displacement dispensers consist of a pressurized chamber and a volumetric piston. As the piston is pulled up, pressure in the chamber decreases and fluid is drawn through a valve to the main chamber of the dispenser. When the piston moves back down, pressure increases, and material directly equal to the swept volume of the piston is forced to exit the chamber through a set of one or more configured valves. Piston dispensers can repeat this process in a variety of pressure settings and are able to operate with highly viscous materials. The mechanical nature of this operation allows it to repeatability dispense accurate volumed despite material variants such as temperature or viscosity.
Dispensers that are piston-driven are ideal when dispensing singular shots. Something to be aware of with this type of dispenser is that the shot size can only be as large as the piston itself. GP Reeves manufactures dispensers with pistons over 1000 cc, however if your application requires a large amount of material very quickly, a rotary dispenser may be better suited.
Positive-displacement rotary pumps offer a great method of continuous flow dispensing. These utilize rotary motion instead of reciprocating motion for operating, like other positive displacement options. Rotary pumps do not require check valves since a dynamic seal exists to provide for the continuous flow of material. After material enters the chamber, it moves from the suction side pump to the exit side of the pump. There are several types of rotary pumps, common ones including gear pumps and peristaltic pumps. Both versions allow high-viscosity fluids to be pumped with a minimal reduction in efficiency and durability.
Material moves through gears which ensure that it is transferred with accuracy and minimal leakage. Internal and external gear pumps are available. Both types have two internal gears. The internal type of pump features one gear inside of another; the material will flow inside the larger gear and be moved by the smaller gear. External gear pumps feature two gears that sit next to each other; material flows around and between these gears. Our VFMG series of flow sensor functions in this way. Gear pumps generally require a consistent calibration schedule to ensure that any ware on the gears is accounted for into the volume measurement.
Internal Gear Pump
External Gear Pump
Material is transferred through a flexible tube (light orange) which is contained around the outskirts of the pump chamber. The pump’s rotor (dark purple) has rollers attached to its outer edge, which compress the tube and cause the body of fluid to be continuously pushed. Peristaltic pumps ensure accurate volume measurement using the amount of tubal space between each of the rollers. These types of pumps work well for corrosive or reactive materials because the material being pumped will only ever touch the tube and the material of the tube can be customized based on each application.
Material moves through the chamber in the cavities of a screw. As the pump’s rotor turns, material flows from cavity to cavity with a flow rate that is proportional to the rotation rate. As the amount of fluid in one cavity dwindles, the volume of another simultaneously increases so there is not a pause in the overall flow process.
Time Pressure Dispense
Time pressure dispensers work by moving material under pressure through an “Off-On” valve that is opened and closed by a solenoid valve controlled by a PLC or electronic timer. Pressure regulators and adjustable orifices are sometimes added to monitor or control flow rate. Time pressure dispensers’ function like a faucet and require constant volume monitoring to remain precise.
Material’s flow characteristics are often unpredictable meaning timed dispensers are not capable of accuracy and repeatability for them. Thicker materials move significantly slower than thin ones, which would lead to less thick material being dispensed in the same time frame. External variants such as temperature and humidity can impact the viscosity of materials throughout a single day leading to inconsistent dispense volumes when utilizing a time pressure dispense system. The exact volume of how much material is dispensed on the part would be unknown unless a weight is measured of each part before and after the dispense.
If precision and repeatability aren’t a top priority, a time pressure system may work fine for your application, however if repeatability (down to the hundredth of a cc!) is important, positive displacement dispensers are the way to go. Positive displacement systems offer advantages that cause production lines to be more efficient, sustainable, and accurate. Lucky for you, the team at GP Reeves is committed to innovating positive displacement to the top of its game by providing only the most optimal solutions for each application. The mechanical innovation of our positive displacement systems ensures your assembly is conducted with cutting-edge precision and repeatability. Whether a piston, rotary, or diaphragm pump makes most sense for your manufacturing process, you’ll be guaranteed an extensive level of care and quality from a GP Reeves dispense system.
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