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Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical vegetation and refineries. Fischer is also a part-time college professor. He is the principal reliability advisor for Fischer Technical Services. He could additionally be reached at bobfischer@fischertechnical.com.
One of Dirty Harry’s famous quotes was: “A man’s got to know his limitations.” diaphragm seal illustrates why you should know your management valve’s limitations.
A shopper lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in too much heat from the prevailing burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product however the burners were guzzling 110 gallons of propane each hour. Given the excessive price of propane at that plant, there were, actually, millions of incentives to preserve energy and cut back prices.
Figure 1. Operation of a cross linked air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers book could be discovered online at https://online.flippingbook.com/view/852569. Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
A capital challenge to retrofit smaller burners was being written. One of the plant’s engineers known as for a worth estimate to alter burner controls. As we mentioned their efforts to reduce back gasoline utilization, we realized smaller burners won’t be required to unravel the problem.
Oxidizer temperature is mainly decided by the place of a “combustion air” control valve. Figure 1 shows how opening that valve increases strain within the combustion air piping. Higher stress forces more air through the burners. An “impulse line” transmits the air pressure to one side of a diaphragm within the “gas control valve” actuator. As air strain on the diaphragm increases, the diaphragm moves to open the valve.
The gas valve is automatically “slaved” to the combustion air being supplied to the burner. ไดอะแฟรม is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to hold up flame stability at considerably lower fuel flows as a end result of there’s a restricted vary over which any given diaphragm spring actuator can present correct control of valve place. This usable management range is named the “turndown ratio” of the valve.
In this case, the plant operators not wanted to totally open the fuel valve. They needed finer decision of valve place with a lot decrease combustion air flows. The diaphragm actuator wanted to have the flexibility to crack open and then management the valve utilizing significantly lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the fuel valve actuator — using the prevailing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No important downtime. Only a number of inexpensive components and minor rewiring were required to keep away from wasting “a fistful of dollars.”

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