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 be a part-time faculty professor. He is the principal reliability consultant for Fischer Technical Services. He may be reached at bobfischer@fischertechnical.com.
One of Dirty Harry’s well-known quotes was: “A man’s received to know his limitations.” This story illustrates why you should know your control valve’s limitations.
เกจวัดอาร์กอน known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much heat from the prevailing burners. All makes an attempt to lower temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t hurt the product however the burners had been guzzling 110 gallons of propane each hour. Given the excessive cost of propane at that plant, there were, literally, millions of incentives to conserve vitality and scale back prices.
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 on-line at https://online.flippingbook.com/view/852569. 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 price estimate to alter burner controls. As we discussed their efforts to reduce fuel utilization, we realized smaller burners won’t be required to solve the problem.
เครื่องมือวัดความดัน is mainly determined by the place of a “combustion air” management valve. Figure 1 exhibits how opening that valve will increase stress in the combustion air piping. Higher pressure forces extra air by way of the burners. An “impulse line” transmits the air stress to 1 side of a diaphragm within the “gas management valve” actuator. As air stress on the diaphragm increases, the diaphragm moves to open the valve.
The fuel valve is mechanically “slaved” to the combustion air being supplied to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to hold up flame stability at considerably lower gas flows as a result of there’s a limited range over which any given diaphragm spring actuator can present correct management of valve position. This usable management range is called the “turndown ratio” of the valve.
In this case, the plant operators now not needed to completely open the fuel valve. They needed finer resolution of valve position with much decrease combustion air flows. The diaphragm actuator needed to be able to crack open after which control the valve utilizing significantly lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gasoline 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 venture. No burner replacements. No significant downtime. Only a number of inexpensive components and minor rewiring have been required to save lots of “a fistful of dollars.”
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