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 can additionally be a part-time college professor. He 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 received to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A client lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much warmth from the prevailing burners. All makes an attempt to lower temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product but the burners had been guzzling 110 gallons of propane every hour. Given the high cost of propane at that plant, there were, literally, millions of incentives to conserve energy and scale back prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers 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 challenge 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 scale back gas usage, we realized smaller burners won’t be required to unravel the issue.
pressure gauge digital ราคา is principally determined by the position of a “combustion air” control valve. Figure 1 shows how opening that valve increases pressure in the combustion air piping. Higher strain forces more air via the burners. An “impulse line” transmits the air stress to a minimal of one side of a diaphragm within the “gas management valve” actuator. As air strain on the diaphragm increases, the diaphragm strikes to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being supplied to the burner. Diaphragm spring tension is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain flame stability at significantly decrease gas flows as a result of there is a restricted range over which any given diaphragm spring actuator can present correct control 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 totally open the fuel valve. They wanted finer resolution of valve place with much decrease combustion air flows. The diaphragm actuator needed to find a way to crack open and then control the valve utilizing considerably lower 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 definitely approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. No vital downtime. Only a number of inexpensive parts and minor rewiring had been required to keep away from wasting “a fistful of dollars.”

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