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 be a part-time school professor. He is the principal reliability advisor for Fischer Technical Services. He could additionally be reached at
One of Dirty Harry’s famous quotes was: “A man’s received to know his limitations.” This story illustrates why you have to know your management valve’s limitations.
A consumer lately referred to as for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in an extreme amount of warmth from the present burners. All attempts to lower temperatures had ended in unstable flames, flameouts and shutdowns. The greater temperatures didn’t hurt the product however the burners had been guzzling one hundred ten gallons of propane every hour. Given the excessive value of propane at that plant, there have been, literally, tens of millions of incentives to conserve power 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 may be discovered on-line at Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
เครื่องมือวัดpressure to retrofit smaller burners was being written. One of the plant’s engineers known as for a value estimate to alter burner controls. As we discussed their efforts to reduce back fuel utilization, we realized smaller burners won’t be required to unravel the issue.
Oxidizer temperature is mainly determined by the place of a “combustion air” control valve. Figure 1 exhibits how opening that valve will increase stress within the combustion air piping. Higher strain forces extra air by way of the burners. An “impulse line” transmits the air stress to 1 facet of a diaphragm in the “gas management valve” actuator. As air stress on the diaphragm will increase, the diaphragm strikes to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being supplied to the burner. Diaphragm spring tension is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to keep up flame stability at significantly decrease gasoline flows because there’s a restricted vary over which any given diaphragm spring actuator can present accurate management of valve position. This usable control range is called the “turndown ratio” of the valve.
In this case, the plant operators not wanted to totally open the fuel valve. They wanted finer decision of valve position with a lot decrease combustion air flows. The diaphragm actuator wanted to have the ability to crack open and then management the valve utilizing considerably decrease pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to permit recalibration of the gas valve actuator — utilizing the present burners.
Dirty Harry would definitely 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 elements and minor rewiring have been required to save lots of “a fistful of dollars.”


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