Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical vegetation and refineries. Fischer can also be a part-time faculty professor. He is the principal reliability advisor for Fischer Technical Services. He may be reached at
One of Dirty Harry’s famous quotes was: “A man’s got to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A consumer just lately known as for help downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in too much warmth from the existing burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product however the burners had been guzzling one hundred ten gallons of propane every hour. Given the high cost of propane at that plant, there have been, literally, millions of incentives to preserve vitality and scale back prices.
Figure 1. Operation of a cross linked air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers e-book could be discovered online at 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. เกจวัดแรงลม of the plant’s engineers called for a value estimate to change burner controls. As we mentioned their efforts to reduce gasoline utilization, we realized smaller burners might not be required to resolve the issue.
Oxidizer temperature is mainly decided by the position of a “combustion air” management valve. Figure 1 reveals how opening that valve increases pressure within the combustion air piping. Higher stress forces more air via the burners. An “impulse line” transmits the air strain to one side of a diaphragm in the “gas control valve” actuator. As air strain on the diaphragm increases, the diaphragm moves to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being provided to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for stable flame.
The plant was unable to maintain flame stability at considerably lower gas flows as a end result of there is a limited vary over which any given diaphragm spring actuator can present correct control of valve place. This usable management range is called the “turndown ratio” of the valve.
In this case, the plant operators no longer needed to totally open the gasoline valve. They wanted finer decision of valve place with much decrease combustion air flows. The diaphragm actuator needed to find a way to crack open after which control the valve utilizing significantly lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the fuel valve actuator — utilizing the prevailing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. No vital downtime. Only a few inexpensive components and minor rewiring had been required to keep away from wasting “a fistful of dollars.”

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