Power Transmission and Motion Control

Technology Focus part 1

Net- worked Flow
by Jean Thilmany

When it comes to valves, unlike television, plenty of cable isn't necessarily a good thing.

So when two Defense Energy Supply Center fuel depots in Jacksonville, Fla., automated their fuel-handling systems, they got rid of some of the wire.

The depots transfer aviation and marine diesel fuel to other stations and refuel U.S. defense aircraft, ships, and vehicles.

Two Defense Energy Supply Centers in Jacksonville, Fla., recently upgraded to an automatic valve system that consists of actuators connected to a master unit via an Ethernet network.

"We were working with a system that originally required just tons of cabling and wiring for each valve," said Tim Haines, construction superintendent for EnGlobal Design Group of Houston, the design engineering and installation contractor for the system. "We wanted a network system where the valves could be controlled with only two wires."

The solution EnGlobal chose to get rid of the clutter was to use MX actuators controlled by Master Station II network control units from Flowserve Flow Control of Irving, Texas.

The larger of the two facilities at Jacksonville, the Northside Fuel Depot, received 94 actuators and three network control units. The other Jacksonville site, the Mayport Fuel Depot, got 42 actuators and one network control unit. The actuators at each site are connected to the master units over an Ethernet network that was already in place before the changeover went into effect.

The fuel-handling upgrade gave the supply centers greater fueling process accountability and more control in safety management, Haines said.

Filling bottles at the rate of hundreds every minute, you have to keep everything running smoothly. Jerky movements can cause bottles to jam, and then you're into downtime. What's more, system crashes from any cause can damage gears and require expensive repairs.

That's why Elmar Industries, a Depew, N.Y., manufacturer of machines that can fill bottles with food, beverages, or pharmaceuticals, has added mechanical torque limiting devices in addition to the electronic limit switches already on its Monoblock filler/capper machines. The company installed two different mechanical torque limiting devices, supplied by Zero-Max Inc. of Plymouth, Minn., to safeguard separate machine functions: the motorized height adjustment mechanism and the timing screw that moves bottles through the system. The machines can fill and cap 600 containers a minute.

The original design used electronic limit switches to control torque on the height adjustment mechanism. The electronic limit switches, attached to cables by pin connectors, sometimes did not stand up in use, according to Russell Wozniak, project engineer for Elmar. He decided to back up the limit switches with mechanical torque limiters.

Wozniak installed an H-TLC torque limiter, which operates by a spring-loaded pin and detent design, between the motor and the shaft leading to the height adjuster mechanism. The H-TLC reacts to predetermined load setpoints. When the device experiences overload, the pin disengages from a detent, a mechanism that locks and unlocks movement, detaching the drive and shutting down the system. The H-TLC is completely mechanical and is adjustable to different torques. After an overload is corrected, it can be reset quickly and the machine restarted.

A different torque limiter, called a Torque Tender, was installed on the feed screw that sends bottles into the system for filling. Wozniak installed the second device to protect the timing screw mechanism in the main gear drive. If a jammed bottle stops the rotation of the timing device, the Torque Tender instantly disengages the timing screw, shutting down the filler.

The Torque Tender acts as a positive drive coupling during normal machine operation. Input power transfers to a rigidly held pawl, a sliding bolt that permits motion in one direction but prevents it in another, and rotates the outer drive housing and the shaft to which it is connected. If a jam results in unacceptable load, the excessive torque causes the pawl to rotate out of its detent. The assembly is thereby disconnected from the outer drive housing and cuts power to the system to shut it down. The Torque Tender can be reset manually, returning the pawl back into its detent and re-engaging the driveshaft.

Respiratory patients who require home oxygen therapy have traditionally had just two choices for ambulatory therapy: compressed oxygen systems and liquid oxygen systems. Both work just fine, but have the major disadvantage of requiring tanks that need to be replaced or refilled.

A third choice for home therapy, an oxygen concentrator, extracts some air from the room and separates the oxygen from other gases, eliminating the need for tanks. But, traditionally, the concentrator has been a stationary unit about the size of a large suitcase, requiring an electrical connection.

Inogen Corp. of Goleta, Calif., has developed an oxygen concentrator that can be run as either a stationary or portable unit. It is lightweight, offers long battery life, and low noise—three areas that patients defined as keys to improving their quality of life, according to Inogen.

Scroll compressors use true rotary motion, letting them be balanced for nearly vibration-free use.

The company was able to achieve these three goals by replacing the industry-standard piston pump with a rotary scroll compressor as its prime mover, according to Geoff Deane, Inogen's vice president of engineering and chief technology officer. The scroll compressor, which delivers more than 80 percent volumetric efficiency while drawing less than 40 watts, was developed by Air Squared of Broomfield, Colo.

Critical performance criteria for the compressor included low noise and vibration, long life, oil-free operation, light weight, low energy use, and the accuracy of flow and pressure.

"Until we came upon Air Squared's rotary scroll compressor, a piston pump was the only device that came close in the pressure and size range we needed, and it would have required work to isolate the noise and vibration caused by valves and balance issues," Deane said.

The core of the rotary scroll compressor consists of two identical meshed scrolls (involute spirals), which form right- and left-hand components. One scroll is indexed or phased 180 degrees with respect to the other to allow the scrolls to mesh. This indexing motion creates crescent-shaped pockets between the involutes of the meshed scrolls and the base plates to which they're affixed. Air entering the pump gets trapped in these pockets. As the scrolls rotate, the pockets follow the spiral inward, getting progressively smaller and compressing the air. The air is exhausted through a discharge outlet at the center of the scrolls. No valves are needed because the discharge outlet is isolated from the inlet; this reduces noise. And, because the scroll compressors use true rotary motion, they can be dynamically balanced for nearly vibration-free operation, further reducing the noise of the unit.

The scroll compressor inside the Inogen One weighs two pounds, including its motor, and measures 4.5 in. x 3 in x 3.3 in. The Inogen One unit in its entirety weighs less than 10 pounds, including its battery, and measures about 12 in. x 6 in. x 12 in.

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