Peristaltic pumps have become one of the fastest-growing types of positive displacement pumps in the worldwide marketplace. These "tubing pumps" traditionally were used almost exclusively for fluid-handling applications in the medical lab. But times are changing, and peristaltic pumps today serve diverse industries, including chemical process control, pharmaceutical processing, wastewater treatment, and food and beverage.

According to Barnant (Barrington, IL), a leader in peristaltic pump technology, the popularity of peristaltic pumps can also be attributed to their effective design, which integrates an electric motor to turn a set of rollers.

"The pump motor performs a critical function and must perform reliably," reports Brad Blum, OEM design engineer at Barnant, which for decades has turned to Pittman® brush and brushless dc gearmotors.

The rollers compress and release a flexible tube as they pass across the tube. This squeezing action creates a vacuum, which then draws fluid through the tubing to achieve the pumping action. Because the flexible tubing is the only wetted part, corrosion of parts is avoided and maintenance and cleanup become easy.

In addition to its flagship Masterflex® pump line, Barnant offers more than 4,000 products and a specialized capability to custom-design process pump and fluid control solutions. Motors generally are selected, in part, based on the size and formulation of a system's tubing and the required speed of the pump to achieve a desired flow rate.

"But the application will additionally guide us regarding motor design and performance," Blum adds. The issues of size and noise, for example, usually come into play. "With an increasing emphasis on compact product designs, we strive generally to incorporate the smallest possible motor. And spur gears represent our preferred choice for their low noise factor."

When Customization Is Standard

According to Blum, in many cases "standard" motor products will necessarily get customized for an application. He gives high marks to the willingness of the Pittman products team to go the extra miles.

"As examples, a motor may have application-specific mounting configurations, depending on how it will be coupled to the pump head; encoders may be specified for control applications to ascertain flow rates or dispensed amounts of fluid; and other modifications may be needed," he says.

Among the brush-commutated and brushless dc gearmotors finding homes in Barnant pump systems:

Pittman brush dc gearmotors (Series GM8000, GM9000, and GM14000). These can achieve output torque up to 175 oz-in. with the standard sintered steel spur gearing (and output torque up to 500 oz-in. by incorporating select gear ratios and high-strength gears).

Series GM8000 gearmotors provide a range of 11 standard reduction ratios from 6.3:1 to 1803.6:1; Series GM9000 gearmotors offer 12 ratios from 5.9:1 to 4732.5:1; and Series GM14000 gearmotors feature four ratios from 5.9:1 to 218.4:1. "The gear ratios provide us with the means to achieve variable flow rates," Blum notes.

Armatures are skewed to minimize magnetic cogging, even at low speeds. Two-pole permanent magnet stators are constructed with ceramic magnets enclosed in heavy-gauge steel return rings. Diamond-turned commutators contribute to optimized brush life.

Pittman brushless dc gearmotors (ELCOM ST® N2300). These slotted brushless motors incorporate internal Hall sensor feedback for linear speed-torque characteristics, high starting torque, and variable speed control (with appropriate control electronics). Their 6-slot lamination design serves to deliver high power, fast acceleration, consistent operation, and long service life. Speeds up to 8,000 rpm and continuous torque up to 49 oz-in. (75 oz-in. with heat sink) can be achieved.

These types of dc motors have proven well-suited for Masterflex pump applications that require "very long life and more power in a smaller package," according to Blum. They are more compact (2.3 in. diameter) and shorter (standard stack lengths 1/2 in., 1 in., 1-1/2 in., and 2 in.) compared with brush motor models.

Encoders are among the customization options tapped by Barnant, depending on application, and advances for these devices have been significant.

Out of the Lab, Into the Real World

For example, a newly patented Pittman 35mm ROSE (Reflective Optical Sensing) encoder features PC board-based modular design for compactness and an unprecedented capability. Instead of requiring discrete modules for individual line-count applications, this incremental encoder can uniquely achieve multiple line counts using only one module.

Multitracked code discs enable the widest range of resolutions (192, 200, 250, 256, 360, 400, 500, and 512 counts per revolution) using minimal parts.

All the various innovations in motor components and pump systems have served to keep pace with a burgeoning number and types of applications over the years. And underscoring how far peristaltic pumps have traveled from the medical laboratory, Blum cites the following real-world case from Barnant customer files (with Pittman brush dc motor onboard).

"A whiskey manufacturer called one of our application specialists because the distiller sought to automate the system," recounts Blum. "The customer had traditionally tested the density of whiskey using a manual syringe, but now wanted a pump for greater efficiencies. Specific requirements were for a noncontaminating, self-priming, and easy-to-clean pump. We recommended a Masterflex CL tubing pump as the solution.

"The outcome was good all around," Blum says. "The fluid only contacts the tubing, so the cell is always clean; the self-priming pump makes getting a sample much easier; and cleaning the pump means simply throwing the tubing away. And experience tells us that the Pittman motor will perform reliably over time."