Servo or Pneumatic: Which Dispenser Holds Its Volume?

Applying material to a surface requires precision, efficiency, and consistent quality. At GP Reeves, we have built expertise in volumetric dispensing and precision dispensing since our founding in 1971, growing to provide global industry leaders with a range of effective dispensing solutions. Our typical fluid dispensing systems use positive displacement pneumatic or servo dispensers. Below, we explore the differences between these two technologies and how each contributes to the success of your production line.

Positive Displacement Dispensing: How Volumetric Dispensing Works

At GP Reeves, consistency and reliability are top priorities, which is why we focus on the development of positive displacement dispense systems. These systems only need to be set once, eliminating the continuous adjustments required by timed-pressure dispensing. Positive displacement dispensers are also unaffected by external environmental conditions, making them ideal for materials that change viscosity with temperature or humidity. One common type of positive displacement dispenser is the rod system. These systems transfer material under pressure into and out of a measuring chamber using pneumatic or servo-powered dispense rods. The design ensures a consistent, repeatable dispense. The rods are paired with a piston (in pneumatic systems) or a linear actuator (in servo systems), which controls the transfer volume. The dispense rate is directly proportional to the diameter of the dispense rod and its speed. That relationship is represented by the following model, where Q represents the flow rate, Vp is the piston motion velocity, and Dp is the piston diameter.

Two Methods of Positive Displacement Dispensing

With rod-style positive displacement dispensing, there are two common methods: pneumatic and servo-powered. Understanding the distinction is key to selecting the best option for your material delivery needs. Pneumatic rod-style systems use linear motion to dispense material, while servo-powered systems convert rotational motion into linear motion. Despite the difference, both methods offer high accuracy, reliability, and efficiency across a variety of production environments.

Basics of Pneumatic Dispense Systems

Pneumatic rod-style dispensers use a linear position sensor with PID controls, along with compressed air, to drive the dispense rod. The air pressure moves the rod, which displaces the material. Linear position sensors track the rod’s location, providing real-time data on the distance traveled between two points of motion. Operators can program a specific dispense volume, which correlates directly to the rod’s movement distance. The PID controls continuously monitor the piston rod’s position within the dispense chamber and adjust air pressure accordingly, ensuring a steady dispense rate. This system offers a high level of accuracy, but the reliance on air pressure means the dispensing rate may not be as consistent as in servo-powered systems.

Basics of Servo-Powered Dispense Systems

Servo-powered positive displacement rod-style dispensers electromechanically convert the rotary motion of a motor into linear motion. The conversion happens through a ball screw within the linear actuator, which adjusts dispensing speed and affects the overall torque of the system. The motor directly controls the speed and force of the actuator, enabling precise movement. In this type of system, the servo motor drives the dispense rod, which moves material out of the measuring chamber. The system delivers repeatable, consistent dosage volumes with each dispense. Operators can program the desired flow rate and volume, and the servo motor executes those parameters through controlled rotary motion. Unlike pneumatic systems, servo-driven dispensers maintain their programmed rate and volume regardless of external conditions, ensuring consistent performance even in fluctuating atmospheres.

Choosing Pneumatic vs Servo

Now that you are familiar with the basic principles of pneumatic and servo-powered positive displacement systems, you can make a more informed decision about which suits your production needs. To simplify the process, we have outlined the key considerations of each, so you can compare the benefits they offer your assembly process.

Servo

• Automatically adjusts rotary force to compensate for changes in temperature, air pressure, or material viscosity
• Electromechanically calculates the distance required for the piston rod to move
• Ideal for applications where verifiable dispense volumes are critical
• Offers greater control without the need to modify the air cylinder size
• Capable of maintaining tighter tolerances
• Easier to operate, integrate, and fine-tune

Final Thoughts Choosing Your Volumetric Dispensing System

The decision between a servo or pneumatic system often depends on the specifics of your application, and it may ultimately come down to operational preference and your preferred programming method. Both pneumatic and servo-powered positive displacement dispensers deliver accuracy and efficiency. With proper maintenance and adherence to safety guidelines, both can significantly improve your production process. To explore which option is right for you, contact our team of dispensing expertsto discuss your servo or pneumatic positive displacement system needs.