Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical plants and refineries. Fischer can be a part-time college 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 want to know your management valve’s limitations.
A client lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much warmth from the existing burners. All attempts to lower temperatures had led to unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product however the burners have been guzzling 110 gallons of propane every hour. Given the high cost of propane at that plant, there were, literally, tens of millions of incentives to preserve energy and reduce costs.
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 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. One of the plant’s engineers called for a price estimate to change burner controls. As we mentioned their efforts to reduce gasoline usage, we realized smaller burners might not be required to unravel the problem.
Oxidizer temperature is mainly determined by the position of a “combustion air” management valve. Figure 1 reveals how opening that valve will increase strain in the combustion air piping. Higher pressure forces extra air via the burners. An “impulse line” transmits the air strain to 1 side of a diaphragm within the “gas control valve” actuator. As air pressure on the diaphragm will increase, the diaphragm moves to open the valve.
The gas valve is mechanically “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 keep up flame stability at significantly decrease gasoline flows as a outcome of there’s a limited vary over which any given diaphragm spring actuator can provide accurate management of valve place. This usable management range is named the “turndown ratio” of the valve.
In this case, the plant operators not needed to totally open the fuel valve. They needed finer decision of valve place with much decrease combustion air flows. The diaphragm actuator wanted to have the ability to crack open and then control the valve using 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 — utilizing the existing burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. จำหน่ายเกจวัดแรงดัน . No important downtime. Only a few inexpensive components and minor rewiring had been required to save “a fistful of dollars.”

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