Peristaltic pumps use rotating rollers pressed against special flexible tubing to create a pressurized flow. The media is moved through the tube with each rotating motion. A rotor with a number of 'rollers', 'shoes' or 'wipers' attached to the external circumference compresses the flexible tube.

As the rotor turns, the part of tube under compression closes (or 'occludes') thus forcing the fluid to be pumped to move through the tube. Additionally, as the tube opens to its natural state after the passing of the cam ('restitution') fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract.

The tubing in peristaltic pumps is often replaceable or disposable. Some manufacturers will give standard choices of materials for tubing or hose including Autoprene, Silicon, and other polymer materials. Silicone rubber is often used in laboratory applications when abrasive and caustic fluids or gases are used. The inner diameter of the tubing is a consideration when working with highly viscous fluids since it will directly affect the flow rate.

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The individual components of peristaltic pumps include a pump head, drive, and tubing. Peristaltic pumps are also referred to as flexible member pumps, flexible tube pumps, dispensing pumps, or dosing pumps.

1. Flow control for Peristaltic pump

The principal limitation of the peristaltic pump is that its fluid delivery is not absolutely uniform. There is a trade-off with the tubing diameter between uniform delivery and lifetime and convenience. For some applications, this is not a problem but for others it is.

Operating a peristaltic pump without any type of flow monitoring or flow control typically has the following disadvantages:

  • Pumps require frequent calibration to correlate flow rate and pump speed;
  • Flow can vary as much as 10-30 percent due to variations in operating pressures;
  • Process optimization is difficult since flow for each process step is uncontrolled;
  • Low- or no-low-flow conditions may occur due pump or other failures leading to damage or scrapped wafers.

One of the possible solutions consists of implementing a closed-loop flow control system that may increase overall tool uptime. Tools operators will no longer need to calibrate the peristaltic pumps, because the controller automatically increases or decreases the pump speed to meet the flow rate requirements.

A closed-loop flow control system will maintain a constant flow rate at a desired flow set-point by increasing or decreasing the pumping speed of the peristaltic pump.

For closed-loop flow control application, the flowmeter must respond quickly to flow changes and must not be affected by the presence of bubbles in the fluid stream.

Implementing a closed-loop flow control system can have the following advantages:

  • Eliminates the need for frequent pump calibrations and increases tool uptime;
  • Maintaining a constant flow of fluid at the desired flow rate Allows for process optimization during each step by controlling fluid flow;
  • Provide process alarms for low or no-low flow conditions;
  • Minimizes fluid waste