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 is also a part-time faculty professor. เกจวัดแรงดันดิจิตอลราคา is the principal reliability advisor 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 have to know your control valve’s limitations.
A shopper lately called for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in an excessive amount of heat from the prevailing burners. All makes an attempt to lower temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t harm the product but the burners have been guzzling 110 gallons of propane each hour. Given the high cost of propane at that plant, there were, actually, millions of incentives to preserve power and reduce prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers e-book could 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 venture to retrofit smaller burners was being written. One of the plant’s engineers called for a worth estimate to change burner controls. As we discussed their efforts to scale back gasoline utilization, we realized smaller burners won’t be required to solve the issue.
Oxidizer temperature is basically decided by the position of a “combustion air” management valve. Figure 1 exhibits how opening that valve increases pressure within the combustion air piping. Higher stress forces more air via the burners. An “impulse line” transmits the air strain to at least one side of a diaphragm in the “gas management valve” actuator. As air strain on the diaphragm increases, the diaphragm moves to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being equipped to the burner. Diaphragm spring rigidity is adjusted to deliver the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to keep up flame stability at considerably lower gas flows as a outcome of there’s a limited range over which any given diaphragm spring actuator can provide correct management of valve position. This usable control vary is known as the “turndown ratio” of the valve.
In this case, the plant operators not needed to fully open the gas valve. They needed finer resolution of valve place with much decrease combustion air flows. The diaphragm actuator wanted to be able to crack open after which control the valve using significantly decrease pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to permit recalibration of the gas valve actuator — using the present burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No vital downtime. Only a quantity of inexpensive elements and minor rewiring were required to save lots of “a fistful of dollars.”

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