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 college professor. He is the principal reliability consultant for Fischer Technical Services. He could also be reached at
One of Dirty Harry’s well-known quotes was: “A man’s received to know his limitations.” This story illustrates why you want to know your control valve’s limitations.
A shopper recently referred to as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much warmth from the existing burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product however the burners had been guzzling one hundred ten gallons of propane each hour. Given the excessive price of propane at that plant, there have been, literally, hundreds of thousands of incentives to preserve energy 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 may be found 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 referred to as for a worth estimate to change burner controls. As we discussed their efforts to minimize back gas utilization, we realized smaller burners might not be required to solve the issue.
Oxidizer temperature is principally decided by the position of a “combustion air” control valve. Figure 1 exhibits how opening that valve increases stress in the combustion air piping. Higher strain forces extra air through the burners. An “impulse line” transmits the air strain to one aspect of a diaphragm in the “gas control valve” actuator. As air pressure on the diaphragm will increase, the diaphragm moves to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being provided to the burner. เกจวัดแรงดันpcp is adjusted to deliver the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to take care of flame stability at considerably decrease fuel flows as a end result of there is a restricted vary over which any given diaphragm spring actuator can provide accurate control of valve place. This usable control vary is known as the “turndown ratio” of the valve.
In this case, the plant operators now not needed to fully open the fuel valve. They needed finer resolution of valve position with much lower combustion air flows. The diaphragm actuator wanted to find a way to crack open after which control the valve utilizing considerably lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the gas valve actuator — utilizing the existing burners.
Dirty Harry would definitely approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No vital downtime. Only pressure gauge nuova fima ราคา and minor rewiring had been required to save “a fistful of dollars.”

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