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 additionally be a part-time school professor. He is the principal reliability consultant for Fischer Technical Services. He could also 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 should know your control valve’s limitations.
A client lately referred to as for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in an extreme amount of warmth from the prevailing burners. All attempts to lower temperatures had resulted in unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product however the burners were guzzling one hundred ten gallons of propane every hour. Given the excessive cost of propane at that plant, there have been, actually, tens of millions of incentives to conserve vitality and cut 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 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.
ที่วัดแรงดันน้ำ 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 solve the problem.
Oxidizer temperature is basically determined by the place of a “combustion air” control valve. Figure 1 exhibits how opening that valve will increase strain within the combustion air piping. Higher pressure forces extra air via the burners. An “impulse line” transmits the air pressure to 1 side of a diaphragm within the “gas management valve” actuator. As air stress on the diaphragm will increase, the diaphragm strikes to open the valve.
The gas valve is automatically “slaved” to the combustion air being supplied to the burner. Diaphragm spring tension is adjusted to deliver the 10-to-1 air-to-gas ratio required for stable flame.
The plant was unable to maintain flame stability at significantly decrease gasoline flows because there is a restricted range over which any given diaphragm spring actuator can present correct management of valve place. เกจวัดแก๊สlpg is named the “turndown ratio” of the valve.
In this case, the plant operators no longer needed to fully open the gasoline valve. They wanted finer resolution of valve place with a lot lower combustion air flows. The diaphragm actuator wanted to find a way to crack open after which management the valve utilizing considerably decrease pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gas 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 challenge. No burner replacements. No vital downtime. Only a number of inexpensive components and minor rewiring have been required to save “a fistful of dollars.”

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