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Intelligent control wards off breakdowns.

Plastics manufacturers and pharmaceutical companies are preventing equipment failure and scheduling maintenance downtime more conveniently by replacing their control valves with the StarPac intelligent control valve system developed by the StarSystems division of Valtek Inc. (Provo, Utah). This noninvasive system measures and controls the flow, pressure, and temperature within fluid-processing loops.

The StarPac system consists of two pressure sensors, each body mounted upstream and downstream of the valve seat. These are used to measure the pressure drop within the valve. A position sensor is located on the valve yoke to measure the stem position, which indicates to what degree the valve is open.

Valtek technicians also locate a thermowell in the valve body within the minimal wall thickness. A thermocouple measures temperature for fluid density correction and vapor pressure to predict choked flow.

Sensor signals are sent to the StarPac's electronics package, where they are converted to digital and analog information. Algorithms to convert the valve pressure data into full-line pressure data were calculated by Dennis O'Hara, senior project engineer at Valtek. "We also developed software that enables StarPac to work with most digital communication protocols, interfacing with either a personal computer, for local site control, or a plant-wide distributed-control system," said O'Hara. Starpac is equipped with an internal relay for manual mode operation when necessary. The StarPac data logger and totalizer provide information to produce historical trends of valve and process performance.

StarPac can function in temperatures ranging from cryogenic to 1200[degrees]F and pressures ranging from vacuum to 20,000 psi with liquids, gases, and slurries. Cape Industries Inc. (Wilmington, N.C.) uses StarPac to control the flow of the viscous high-temperature polymer it uses to make dimethyl terephthalate (DMT). DMT from the plant is used to make film, polyester fibers, bottle resin, and engineered plastics.

In an environmentally driven application, a StarPac valve was installed by pharmaceutical manufacturer Merck & Co. Inc.'s Rahway, N.J., bulk pharmaceutical plant to control water flow to a hydrochloric acid scrubber. Inadequate flow could cause the scrubber to fail and release emissions.

O'Hara is currently developing an expert version of Starpac that wifl inform operators how the valve is performing while on-line. "The expert version will display valve information, such as whether the valve's packing is leaking, in plain English. This will eliminate the need for graphs and charts and for site visits by service technicians," O'Hara said.

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Title Annotation:control valves from Valtek Inc.
Author:Valenti, Michael
Publication:Mechanical Engineering-CIME
Date:Jul 1, 1993
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