Why Positive Displacement is the Key to Precision

There are several types of material dispensers commonly used in the manufacturing process, with positive displacement dispensers and time/pressure dispensers being the most prevalent. While both offer distinct advantages, positive displacement dispensers are often regarded as the superior option for precise dispensing. Their ability to deliver exceptional accuracy, reduce material waste, offer versatility across various applications, and maintain precise volume control makes them the optimal choice for many manufacturing systems.

Positive displacement encompasses a broad range of dispenser types, generally referring to the movement of pressurized material through an enclosed chamber using mechanical means such as pistons, gears, or screws. This method’s automated nature enables positive displacement dispensers to achieve a higher level of precision compared to time/pressure dispensers. The specific type of positive displacement dispenser chosen depends entirely on the application. Gear, screw, and peristaltic pumps are ideal for continuous flow applications, while piston pumps, although limited to dispensing volumes as large as the piston, offer superior accuracy.

Piston-driven dispensers are ideal for applications requiring precise, singular shots of material. However, it’s important to note that the shot size is limited by the piston’s capacity. At GP Reeves, we offer piston dispensers with capacities exceeding 1000 cc, ensuring flexibility for various needs. That said, if your application demands a high volume of material in a short amount of time, a rotary dispenser may be a more suitable option due to its ability to deliver continuous flow at a faster rate.

Positive-displacement rotary pumps provide an effective solution for continuous flow dispensing by utilizing rotary motion rather than the reciprocating action found in other positive displacement systems. Unlike piston-driven pumps, rotary pumps do not require check valves, as the dynamic seal ensures a steady, uninterrupted flow of material. Once the material enters the pump chamber, it is moved from the suction side to the discharge side in a smooth, continuous motion. Several types of rotary pumps exist, including gear and peristaltic pumps, both of which are well-suited for handling high-viscosity fluids while maintaining excellent efficiency and durability.

External Gear Pump

In peristaltic pumps, the pump chamber contains a flexible tube (often light orange) that transports material along its outer edge. The pump’s rotor (typically dark purple) is equipped with rollers on its outer perimeter that compress the tube, pushing the fluid forward in a continuous motion. These pumps provide accurate volume measurement by controlling the amount of space within the tube between each roller. Peristaltic pumps are ideal for handling corrosive or reactive materials, as the fluid only comes into contact with the tube. Additionally, the tube material can be customized to suit the specific requirements of each application, enhancing both durability and compatibility.

Time pressure dispensers operate by moving material under pressure through an “on-off” valve, controlled by a solenoid valve connected to a PLC or electronic timer. In some cases, pressure regulators and adjustable orifices are added to control or monitor flow rate. These dispensers function much like a faucet, and constant volume monitoring is required to maintain precision.

However, time pressure dispensers can face challenges with accuracy and repeatability due to the unpredictable nature of material flow. Thicker materials move more slowly than thinner ones, resulting in smaller quantities being dispensed within the same time frame. External factors, such as temperature and humidity, can also impact material viscosity throughout the day, leading to inconsistent dispense volumes. Without measuring the weight of each part before and after dispensing, the exact amount of material dispensed remains unknown.

While time pressure systems may be sufficient for applications where precision and repeatability are not critical, for processes requiring high accuracy (down to the hundredth of a cc), positive displacement dispensers are the superior choice. Positive displacement systems offer unmatched efficiency, sustainability, and precision, making them ideal for production lines where accuracy is paramount.

At GP Reeves, we are dedicated to advancing positive displacement technology to the highest standards, providing tailored solutions for every application. Whether a piston, rotary, or diaphragm pump best suits your manufacturing process, our systems are designed to ensure cutting-edge precision and repeatability. With a GP Reeves dispense system, you can count on extensive care and superior quality in every aspect of your assembly.