Fischer: Know your valve’s limitations 

Robert L. เกจวัดแรงดันsumo , P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can also be a part-time college professor. He is the principal reliability marketing consultant for Fischer Technical Services. He could also be reached at
One of Dirty Harry’s well-known quotes was: “A man’s received to know his limitations.” This story illustrates why you have to know your control valve’s limitations.
A shopper recently referred to as for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in an excessive quantity of warmth from the present burners. All makes an attempt to decrease temperatures had resulted in unstable flames, flameouts and shutdowns. The greater temperatures didn’t hurt the product but the burners had been guzzling 110 gallons of propane each hour. Given the excessive price of propane at that plant, there were, actually, millions of incentives to conserve vitality and cut back costs.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers e-book can be found on-line 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 alter burner controls. As we discussed their efforts to reduce fuel utilization, we realized smaller burners may not be required to resolve the issue.
Oxidizer temperature is principally determined by the place of a “combustion air” management valve. Figure 1 reveals how opening that valve increases pressure in the combustion air piping. Higher stress forces extra air via the burners. An “impulse line” transmits the air stress to a minimal of one aspect of a diaphragm within the “gas control valve” actuator. As air stress on the diaphragm increases, the diaphragm moves to open the valve.
The gas valve is mechanically “slaved” to the combustion air being supplied 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 maintain up flame stability at significantly lower gas flows as a end result of there is a limited vary over which any given diaphragm spring actuator can present accurate management of valve place. This usable control range is called the “turndown ratio” of the valve.
In this case, the plant operators no longer needed to completely open the gas valve. They wanted finer decision of valve place with a lot decrease combustion air flows. The diaphragm actuator needed 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 undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. ร้านซ่อมเครื่องวัดความดัน . Only a few cheap elements and minor rewiring had been required to save heaps of “a fistful of dollars.”

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