Applying material to a surface can be a complex task. Operators want to achieve great levels of precision, accomplish operational efficiency, and obtain the highest quality results possible. GP Reeves has accumulated a wealth of experience in precision dispensing since its founding in 1971, and since then, our team has grown to provide global industry leaders with a variety of effective dispensing solutions. Our typical fluid dispensing solutions involve positive displacement pneumatic or servo dispensers. Join us for a deep dive into these concepts, where we’ll explain servo vs pneumatic dispensing and how they contribute to the success of your production line!

Positive Displacement Dispensing

GP Reeves prioritizes consistency and reliability, which is why we specialize in the cutting-edge development of positive displacement dispense systems. Positive displacement systems must only be set once, so continuous readjustment involved in timed-pressure dispensing isn’t necessary. Additionally, positive displacement dispensers will not be influenced by external environmental conditions. This is especially important when working with materials that might change viscosity under certain conditions, such as temperature or humidity.

One type of positive displacement dispenser is a rod system. These types of positive displacement dispensers work by transferring material under pressure into and out of a measuring chamber utilizing pneumatic or servo-powered dispense rods. These systems ensure a consistent and repeatable dispense of material. The dispense rods are paired with a piston (for pneumatic systems) or a linear actuator (for servo systems) which then controls the transfer volume. The rate of dispense is directly proportional to the diameter of the dispense rod and the dispense rod speed, as shown in the following model, where Q is the flow rate, Vp the piston motion velocity, and Dp the diameter of piston.

Methods of Positive Displacement Dispensing

With rod-style positive displacement dispensing, there are two common methods of dispensing. It’s important to distinguish between the two to determine the best method for your material delivery. Pneumatic versions of rod-style positive displacement dispense systems naturally possess linear motion, while servo-powered versions dispense systems convert rotational motion to linear motion. Although they might be different, both methods provide accuracy, reliability, and an efficient method for effective material dispense.

Basics of Pneumatic Dispense Systems

Pneumatic rod-style dispensers utilize a linear position sensor with PID controls as well as compressed air to move the dispense rod. The air pressure is what pushes the dispense rod, displacing the material. Linear position sensors monitor the location of the dispense rod and can give a distance range between two points of changed position. For pneumatic dispensing systems, operators can program a certain dispense volume which directly correlates to a distance for the dispense rod to move. The PID controls continuously monitor the location of the piston rod throughout the dispense chamber and adjust the amount of air pressure applied, maintaining a steady dispense rate. Though the system is extremely accurate, the use of air does mean the rate is not as consistent as a servo-powered system.

Basics of Servo-Powered Dispense Systems

Servo-powered positive displacement rod-style dispensers work by electromechanically converting the rotary motion of a motor into linear motion. A ball screw within the linear actuator is used to reduce or increase the dispenser speed and thus impact the torque force of the overall dispensing system. This is all converted into linear motion via the linear actuator. Therefore, the motor influences the speeds and force of the actuator.

In terms of material dispensing, this type of rod-style positive displacement system depends on the servo motor to move the dispense rod, which then moves material out of the measuring chamber. The dispenser does this repeatedly with a consistent dosage volume at each dispense.

With servo-driven systems, an operator programs a certain desired speed of flow and dispense volume, and the servo motor will produce these results based on a certain rotary motion of its servo. So, no matter what the external atmosphere may comprise, the servo will continue to operate at its programmed rate and volume.

Choosing Pneumatic vs Servo

Now that you’re aware of the basic principles surrounding pneumatic and servo positive dispensing systems, you can better determine which type of dispense system is most optimal for your production needs. To make this decision even easier, we’ve laid out the main considerations of each system so you can easily see the benefits they bring to your assembly process.


  • Uses PI loop controls, where an operator gives a range of distance, and the system will actuate within that range.
  • Requires air pressure in the measuring of distance
  • Cylinder size change required for differing levels of control
  • Often less costly
  • Commonly used in the production of electronics


  • Will automatically adjust rotary force to accommodate for changes in temperature, air pressure, or material viscosity
  • Electromechanically determines the distance that the piston rod must move
  • Most desired when verifiable dispense volumes are a concern
  • Provides more control without needing to change the size of the air cylinder
  • Can hold tighter tolerances
  • Easier to operate, integrate, and tune

Final Thoughts

Although the decision to choose a servo vs pneumatic dispensing system may be based upon the conditions of your application, it can ultimately come down to an operational preference and favored programming method. Both pneumatic and servo powered positive displacement dispensers will provide outstanding accuracy and efficiency to your application. As long as they are properly maintained and the operator is aware of directions and safety recommendations, both options of material dispensing can substantially improve your production method. To get your own servo or pneumatic positive displacement system, get in touch with our team of dispensing experts today!

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