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 also be a part-time school professor. He is the principal reliability consultant 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 need to know your management valve’s limitations.
A shopper just lately referred to as for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in an extreme amount of heat from the present burners. All makes an attempt to decrease temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product however the burners had been guzzling 110 gallons of propane each hour. Given the excessive value of propane at that plant, there have been, literally, hundreds of thousands of incentives to conserve energy and cut back costs.
Figure 1. Operation of a cross linked air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers book can be found on-line at Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
weksler pressure gauge ราคา to retrofit smaller burners was being written. One of the plant’s engineers called for a value estimate to vary burner controls. As we mentioned their efforts to reduce gasoline usage, we realized smaller burners might not be required to unravel the issue.
Oxidizer temperature is basically decided by the position of a “combustion air” management valve. Figure 1 shows how opening that valve will increase pressure within the combustion air piping. Higher pressure forces more air by way of the burners. An “impulse line” transmits the air strain to at least one facet of a diaphragm within 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 equipped to the burner. Diaphragm spring tension is adjusted to deliver the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to maintain flame stability at considerably decrease fuel flows as a end result of there is a limited range over which any given diaphragm spring actuator can provide accurate management of valve position. This usable control range is named the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to completely open the gasoline valve. They wanted finer resolution of valve position with a lot decrease combustion air flows. The diaphragm actuator wanted to have the ability to crack open after which management the valve using significantly lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the fuel 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 vital downtime. Only a quantity of cheap components and minor rewiring were required to avoid wasting “a fistful of dollars.”

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