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 is also a part-time college professor. He is the principal reliability advisor for Fischer Technical Services. He may 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 called for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in an excessive amount of warmth from the existing burners. All makes an attempt to decrease temperatures had led to unstable flames, flameouts and shutdowns. เกจวัดแรงดันไอน้ำ didn’t harm the product however the burners have been guzzling one hundred ten gallons of propane each hour. Given the excessive value of propane at that plant, there were, literally, tens of millions of incentives to preserve energy and reduce costs.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers e-book may 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.
A capital project to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a price estimate to vary burner controls. As we discussed their efforts to scale back gas utilization, we realized smaller burners won’t be required to solve the problem.
Oxidizer temperature is mainly determined by the place of a “combustion air” control valve. Figure 1 exhibits how opening that valve will increase pressure in the combustion air piping. Higher pressure forces extra air via the burners. An “impulse line” transmits the air strain to at least 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 routinely “slaved” to the combustion air being supplied to the burner. Diaphragm spring pressure is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to take care of flame stability at considerably decrease gas flows as a result of there is a limited vary over which any given diaphragm spring actuator can present correct management of valve place. This usable management vary is known as the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to totally open the gasoline valve. They needed finer resolution of valve position with much lower combustion air flows. The diaphragm actuator needed to have the ability to crack open and then management the valve using significantly lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to permit recalibration of the gasoline valve actuator — utilizing the prevailing 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 significant downtime. Only a quantity of inexpensive elements and minor rewiring were required to save “a fistful of dollars.”

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