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Modular design enhances air-powered pump's flexibility

Modular design enhances air-powered pump's flexibility

Brecksville, OH--Engineers first developed air-operated pumps and gas boosters about 50 years ago. These useful devices were put to work in a tremendous range of applications that require liquid transfer at both high and low pressure. They also turn up as gas boosters (intensifiers) in industries that need to handle gasses and volatile liquids at varying pressures and flows.
Across the years since the invention of air-operated pumps, tremendous changes have taken place in the world--but not in the design of air-operated pumps. George Cantley, Sprague engineering manager at Teledyne Fluid Systems, along with his colleagues, saw that lack of change as an opportunity.

Air-operated pumps consist of an air motor that drives a pumping element. As the air motor's piston reciprocates, it drives the smaller pump piston. Pump output pressure varies with the ratio of the two pistons' areas, and the pressure of the air that drives the motor. Manufacturers typically sell these pumps into niche markets, and offer them as integral motor/pump units.

These drawings show output modules that produce very different output pressures. Notice the variations in pump-piston diameter and pump cylinder-wall thickness.

Examining conventional air-operated pumps, Cantley appreciated that each combined two distinct functions: drive power and the delivery of pressurized liquid or gas. By performing those functions with interchangeable modules, Cantley, and his colleagues in marketing, believed Teledyne Fluid Systems could offer air-operated pumps with superior performance and improved flexibility.

The result of his work, the PowerStar(R) 4, consists of a single air-motor module that can drive eight different high-pressure modules. Integral pilot/directional valves in the motor module and check valves in the pump module handle the passage of drive air and the pumped medium. Developed in a project that required somewhat less than two years, the air-operated pump--or perhaps more properly, pump system--uses an air motor with a four-inch-diameter piston. The piston reciprocates within a composite cylinder made from epoxy and filament-wound fiberglass. Gel-coating the cylinder's ID and using a Teflon(R) piston seal energized by an O-ring allows the motor to operate on dry shop air.

Openings in the bulkheads on either end of the motor permit users to screw pump modules' pistons into the air motor's piston. Coaxial, stepped counterbores in the bulkheads allow the motor to receive pump cylinders of two different diameters. Changing pump piston diameter, and changing the diameter and wall thickness of the cylinder within which the pump piston reciprocates, creates output modules with different output pressures.

Modularity enables a single air motor to drive eight different pumping modules. This system can produce liquid at pressures from zero to 33,000 psi.

The motor of the PowerStar 4 can drive a single pump module, or it can be set up in a double-ended configuration. In that arrangement, the PowerStar 4 can drive two pump modules of identical output, or pumps of different output. That latter arrangement can be used (for example) to generate two streams of different liquids at a fixed ratio for a mixing system.

Cantley and his colleagues found that the module designed to provide the highest output pressure (33,000 psi) presented some special problems. Engineers needed to minimize diametral clearance between the stainless steel piston and its cylinder, also made from stainless steel. This combination--not a great surprise--caused galling. Surface-hardening the cylinder solved the problem. "The process brought the surface up to about Rockwell 70," says Cantley.

In addition, a seal retaining ring on the high-pressure module experienced considerable wear under test. On one memorable Thanksgiving evening, Cantley stopped by Teledyne Fluid Systems' lab to check on the 33,000 psi module as it pumped oil during a life test. He found the lab a half-inch deep in oil. To solve the problem, he and his colleagues replaced the ring with a thicker one made from 17-4 stainless.

Stainless steel components and Teflon(R) seals, used throughout the pump modules, help make them suitable for essentially all likely applications. Four threaded fasteners secure the pump modules to the air motor. Pump enclosures fit over the motor exhaust ports, and the cool, expanding exhaust exits the pump module enclosure after passing through a sound-absorbing material. This arrangement employs the volume inside the pump housing as a muffler. Cantley and his associates use the exhaust air to cool the liquid pump module, which can run hot. Furthermore, heat from the high pressure pump module prevents ice formation at the motor exhaust, a common problem in conventional air-driven pumps. PowerStar 4 can move 6 gpm in a double-ended configuration. "That's a lot of flow for a small, air-driven pump," says Cantley.

Additional details...Contact George A. Cantley, Teledyne Fluid Systems, 10195 Brecksville Road, Brecksville, OH 44141, (216) 838-7511

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