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 also be a part-time college professor. He is the principal reliability consultant 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 should know your control valve’s limitations.
A shopper just lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in an excessive amount of warmth from the existing burners. เกจวัดแรงดันดิจิตอล makes an attempt to lower temperatures had ended in unstable flames, flameouts and shutdowns. The higher temperatures didn’t harm the product however the burners have been guzzling 110 gallons of propane each hour. Given the high cost of propane at that plant, there have been, actually, millions of incentives to preserve vitality and cut back costs.
Figure 1. Operation of a cross linked air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers book could be discovered 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 referred to as for a value estimate to alter burner controls. As we mentioned their efforts to scale back fuel utilization, we realized smaller burners may not be required to resolve the problem.
Oxidizer temperature is mainly decided by the place of a “combustion air” control valve. Figure 1 reveals how opening that valve will increase stress in the combustion air piping. Higher stress forces extra air via the burners. An “impulse line” transmits the air pressure to one facet of a diaphragm within the “gas control valve” actuator. As air stress on the diaphragm increases, the diaphragm strikes to open the valve.
The gasoline valve is routinely “slaved” to the combustion air being provided to the burner. Diaphragm spring tension 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 considerably lower gas flows because there is a limited vary over which any given diaphragm spring actuator can provide accurate management of valve position. This usable control vary is known as the “turndown ratio” of the valve.
In this case, the plant operators no longer needed to totally open the fuel valve. They wanted finer decision of valve position with much decrease combustion air flows. The diaphragm actuator wanted to have the ability to crack open and then control the valve using considerably decrease pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the fuel valve actuator — using the existing burners.
Dirty Harry would undoubtedly 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 parts and minor rewiring were required to avoid wasting “a fistful of dollars.”


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