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 be a part-time school professor. He is the principal reliability advisor for Fischer Technical Services. He could also be reached at
เกจวัดแรงดันน้ำประปาราคา of Dirty Harry’s well-known quotes was: “A man’s obtained to know his limitations.” This story illustrates why you have to know your control valve’s limitations.
A shopper lately known as for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in an extreme quantity of heat from the present burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product but the burners had been guzzling 110 gallons of propane each hour. Given the high value of propane at that plant, there have been, literally, tens of millions of incentives to preserve energy and scale back costs.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers book could 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 venture to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a price estimate to alter burner controls. As we mentioned their efforts to reduce gasoline usage, we realized smaller burners won’t be required to solve the problem.
Oxidizer temperature is mainly determined by the position of a “combustion air” control valve. Figure 1 shows how opening that valve increases pressure within the combustion air piping. เกจวัดแรงดันไนโตรเจน via the burners. An “impulse line” transmits the air stress to a minimal of one facet of a diaphragm in the “gas management valve” actuator. As air stress on the diaphragm increases, the diaphragm strikes to open the valve.
The gas valve is mechanically “slaved” to the combustion air being equipped to the burner. Diaphragm spring tension is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain up flame stability at considerably decrease gas flows as a result of there is a restricted range over which any given diaphragm spring actuator can present accurate control of valve position. This usable control vary is named the “turndown ratio” of the valve.
In this case, the plant operators now not needed to fully open the gasoline valve. They wanted finer resolution of valve place with a lot lower combustion air flows. The diaphragm actuator needed to be able to crack open after which control the valve utilizing considerably decrease pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gas valve actuator — using 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 significant downtime. Only a few cheap elements and minor rewiring have been required to avoid wasting “a fistful of dollars.”

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