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 is also 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 got to know his limitations.” This story illustrates why you have to know your management valve’s limitations.
A shopper just lately referred to as for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in too much heat from the present burners. All attempts to decrease temperatures had ended in unstable flames, flameouts and shutdowns. The higher temperatures didn’t harm the product however the burners were guzzling one hundred ten gallons of propane every hour. Given the high cost of propane at that plant, there were, actually, tens of millions of incentives to conserve vitality and scale back costs.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers e-book could 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 venture to retrofit smaller burners was being written. One of the plant’s engineers called for a worth estimate to alter burner controls. As we discussed their efforts to scale back fuel utilization, we realized smaller burners may not be required to resolve the problem.
Oxidizer temperature is mainly determined by the position of a “combustion air” control valve. เกจแรงดันน้ำ reveals how opening that valve will increase pressure within the combustion air piping. Higher strain forces extra air by way of the burners. An “impulse line” transmits the air strain to one side of a diaphragm in the “gas control 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 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 maintain flame stability at considerably lower gas flows because there’s a limited range over which any given diaphragm spring actuator can present 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 wanted to totally open the gasoline valve. They wanted finer resolution of valve position with much lower combustion air flows. The diaphragm actuator wanted to be able to crack open after which control the valve utilizing 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 prevailing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No significant downtime. Only a couple of inexpensive elements and minor rewiring had been required to avoid wasting “a fistful of dollars.”

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