Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can additionally 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 well-known quotes was: “A man’s obtained to know his limitations.” This story illustrates why you need to know your management valve’s limitations.
A shopper recently called for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much warmth from the prevailing burners. All makes an attempt to decrease temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product but the burners were guzzling 110 gallons of propane every hour. Given the high price of propane at that plant, there have been, literally, hundreds of thousands of incentives to conserve energy and reduce prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers guide can 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 called for a value estimate to change burner controls. As we discussed their efforts to scale back gasoline utilization, we realized smaller burners might not be required to solve the problem.
Oxidizer temperature is mainly determined by the place of a “combustion air” management valve. Figure 1 reveals how opening that valve increases stress within the combustion air piping. Higher pressure forces more air via the burners. An “impulse line” transmits the air strain to 1 facet of a diaphragm in the “gas control valve” actuator. As air stress on the diaphragm increases, the diaphragm moves to open the valve.
ราคาเพรสเชอร์เกจ is mechanically “slaved” to the combustion air being equipped to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain flame stability at considerably decrease fuel flows because there’s a restricted vary over which any given diaphragm spring actuator can provide correct control of valve place. This usable control vary is identified as the “turndown ratio” of the valve.
In this case, the plant operators now not needed to completely open the gasoline valve. They wanted finer decision of valve position with a lot decrease combustion air flows. The diaphragm actuator wanted to find a way to crack open and then control the valve using significantly decrease pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to permit recalibration of the gasoline valve actuator — using the existing burners.
Dirty Harry would definitely approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No significant downtime. Only a few inexpensive components and minor rewiring were required to save “a fistful of dollars.”

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