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 is also a part-time school professor. He is the principal reliability marketing consultant for Fischer Technical Services. He may be reached at
One of Dirty Harry’s famous 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 just lately referred to as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in too much warmth from the existing burners. All 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 had been guzzling 110 gallons of propane each hour. Given the high cost of propane at that plant, there were, literally, tens of millions of incentives to conserve energy and reduce prices.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers guide 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.
A capital project to retrofit smaller burners was being written. One of the plant’s engineers called for a worth estimate to change burner controls. As we mentioned their efforts to minimize back fuel utilization, we realized smaller burners may not be required to solve the problem.
Oxidizer temperature is mainly decided by the position of a “combustion air” management valve. Figure 1 reveals how opening that valve will increase pressure within the combustion air piping. Higher stress forces more air via the burners. An “impulse line” transmits the air strain to one facet of a diaphragm in the “gas management valve” actuator. As air pressure on the diaphragm will increase, the diaphragm strikes to open the valve.
The gasoline valve is automatically “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 steady flame.
The plant was unable to maintain flame stability at considerably lower gas flows as a end result of there’s a restricted vary over which any given diaphragm spring actuator can present correct control of valve place. This usable control range is named the “turndown ratio” of the valve.
In this case, the plant operators not needed to totally open the gasoline valve. They needed finer resolution of valve position with a lot lower combustion air flows. The diaphragm actuator wanted to have the ability to crack open and then control the valve using considerably lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gas valve actuator — using the existing burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” เกจวัดแรงดันแก๊สlpg . No burner replacements. No important downtime. Only a couple of inexpensive components and minor rewiring were required to save “a fistful of dollars.”

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