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 obtained to know his limitations.” This story illustrates why you should know your control valve’s limitations.
A shopper recently known as for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much heat from the existing burners. All attempts to lower temperatures had resulted in unstable flames, flameouts and shutdowns. The greater temperatures didn’t hurt the product but the burners have been guzzling a hundred and ten gallons of propane every hour. Given the excessive value of propane at that plant, there have been, literally, millions of incentives to conserve power and reduce 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 may be found online at Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
A capital project to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a worth estimate to alter burner controls. As we discussed their efforts to reduce gasoline utilization, we realized smaller burners won’t be required to resolve the problem.
Oxidizer temperature is principally determined by the position of a “combustion air” management valve. Figure 1 shows how opening that valve will increase strain within the combustion air piping. Higher strain forces extra air by way of the burners. An “impulse line” transmits the air strain to one aspect of a diaphragm within the “gas management valve” actuator. As air strain on the diaphragm increases, the diaphragm strikes to open the valve.
The gas valve is routinely “slaved” to the combustion air being provided to the burner. Diaphragm spring rigidity is adjusted to ship the 10-to-1 air-to-gas ratio required for stable flame.
The plant was unable to hold up flame stability at significantly decrease fuel flows as a result of there’s a restricted vary over which any given diaphragm spring actuator can present correct control of valve place. This usable control range is named the “turndown ratio” of the valve.
In this case, the plant operators no longer needed to totally open the gas valve. They needed finer decision of valve position with a lot decrease combustion air flows. ราคาเกจวัดแรงดันลม wanted to have the ability to crack open and then control the valve using considerably lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the gasoline valve actuator — utilizing the present burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No important downtime. Only a few inexpensive components and minor rewiring were required to keep away from wasting “a fistful of dollars.”

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