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 school professor. He is the principal reliability consultant for Fischer Technical Services. He may 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 should know your control valve’s limitations.
A shopper recently referred to as for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much heat from the present burners. เครื่องมือที่ใช้วัดความดัน 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 a hundred and ten gallons of propane each hour. Given the high value of propane at that plant, there were, actually, millions of incentives to preserve vitality 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 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 known as for a price estimate to change burner controls. As we discussed their efforts to scale back gas utilization, we realized smaller burners won’t be required to resolve the issue.
Oxidizer temperature is basically determined by the place of a “combustion air” management valve. Figure 1 exhibits how opening that valve will increase strain in the combustion air piping. Higher strain forces more air by way of the burners. An “impulse line” transmits the air pressure to one aspect of a diaphragm within the “gas management valve” actuator. As air pressure on the diaphragm will increase, the diaphragm moves to open the valve.
The gas valve is automatically “slaved” to the combustion air being supplied to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to keep up flame stability at significantly lower gasoline flows because there’s a limited vary over which any given diaphragm spring actuator can provide accurate control of valve place. This usable control vary is called the “turndown ratio” of the valve.
In this case, the plant operators now not wanted to fully open the fuel valve. They wanted finer decision of valve position with a lot lower combustion air flows. The diaphragm actuator needed to have the ability to crack open after which management the valve using considerably 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 prevailing 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 a couple of inexpensive parts and minor rewiring were required to save tons of “a fistful of dollars.”

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