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 be a part-time school professor. He is the principal reliability advisor for Fischer Technical Services. He may be reached at
One of Dirty Harry’s famous quotes was: “A man’s got to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A client recently called for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much warmth from the present burners. All attempts to decrease temperatures had resulted in unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product however the burners were guzzling 110 gallons of propane every hour. Given the excessive price of propane at that plant, there were, actually, hundreds of thousands of incentives to conserve vitality and scale back costs.
pressure gauge วัด แรง ดัน . 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 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 venture to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a price estimate to vary burner controls. As we discussed their efforts to scale back gas utilization, we realized smaller burners won’t be required to resolve the problem.
Oxidizer temperature is principally determined by the place of a “combustion air” management valve. Figure 1 exhibits how opening that valve increases strain in the combustion air piping. Higher pressure forces extra air through the burners. An “impulse line” transmits the air pressure to 1 aspect of a diaphragm in the “gas management valve” actuator. As air pressure on the diaphragm will increase, the diaphragm moves to open the valve.
The fuel valve is automatically “slaved” to the combustion air being provided to the burner. Diaphragm spring rigidity is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to take care of flame stability at significantly lower gas flows as a outcome of there’s a restricted range over which any given diaphragm spring actuator can provide accurate management of valve position. This usable management vary is called the “turndown ratio” of the valve.
In this case, the plant operators not wanted to totally open the gasoline valve. They needed finer resolution of valve place with a lot lower combustion air flows. The diaphragm actuator needed to find a way to crack open and then control the valve utilizing significantly 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 prevailing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No important downtime. Only a quantity of cheap parts and minor rewiring were required to save “a fistful of dollars.”

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