Equal percentage

When manipulating a stream whose flow is independently determined, such as flow of a product or a heat-transfer fluid from a fired heater, a three-way valve is used to divert the required flow to the heat exchanger. This does not alter the linearity of the process or its sensitivity to supply variations and even adds the possibility of independent flow variations. The three-way valve shomd have equal-percentage characteristics, and heat-flow control may be even more beneficial. 

FIG. 8-82 Installed flow characteristic as a function of percent of total system head allocated to the control valve (assuming constant head pump, no elevation head loss, and an R equal 30 equal-percentage inherent characteristic). 

Type of trim. Use equal percentage whenever there is a large design uncertainty or wide rangeability is desired. Use linear for small uncertainty cases. 

Limit max/min flow to about 10 for equal percentage trim and 5 for linear. Equal percentage trim usually requires one larger nominal body size than linear. 

If the air leakage rate does not comply with the class requirement, the test shall be extended to include an additional equal percentage of the total surface area. 

Decreasing AP with Increasing Load. AP at Maxi mum Load < 20% of Minimum LoadAP Equal-Percentage... 

Gas Process, Smalt Volume, Less Than 10 ft. of Pipe Between Control Valve and Load Valve Equal-Percentage... 

Proportional To Flow In Series Linear Equal- Percentage... 

You want to control the flow rate of a liquid in a transfer line at 350 gpm. The pump in the line has the characteristics shown in Fig. 8-2, with an 5 in. impeller. The line contains 150 ft of 3 in. sch 40 pipe, 10 flanged elbows, four gate valves, and a 3 x 3 control valve. The pressure and elevation at the entrance and exit of the line are the same. The valve has an equal percentage trim with the characteristics given in Table 10-3. What should the valve opening be to achieve the desired flow rate (in terms of percent of total stem travel) The fluid has a viscosity of 5cP and a SG of 0.85. 

A piping system takes water at 60°F from a tank at atmospheric pressure to a plant vessel at 25 psig that is 30 ft higher than the upstream tank. The transfer line contains 300 ft of 3 in. sch 40 pipe, 10 90° els, an orifice meter, a 2 x 3 pump with a 7 in. impeller (with the characteristic as given in Fig. 8-2) and a 3 x 2 equal percentage control valve with a trim characteristic as given in Table 10-3. A constant flow rate of 200 gpm is required in the system. 

Lambda hyperons. (Other hyperons do not appear in the matter). Moreover, an almost equal percentage of nucleons and hyperons are present in the stellar core at high densities. A strong deleptonization of matter takes place, since it is energetically convenient to maintain charge neutrality through hyperon formation rather than /3-decay. This can have far reaching consequences for the onset of kaon condensation. 

Chamcteristics. By changing the shape of the plug and the seat in the valve, different relationships between stem position and flow area can be attained. The common flow characteristics used are linear trim valves and equal-percentage trim valves as shown in Fig. 7.7. The term equal percentage comes from the slope of the /Ji, curve being a constant fraction off. 

Equal-percentage valves are often used when the pressure drop available over the control valve is not constant. This occurs when there are other pieces of equipment in the system that act as fixed resistances. The pressure drops over these parts of the process vary as the square of the flow rate. We saw this in the examples discussing control valve sizing. 

Furthermore, the survey data show that an about equal percentage of black and white respondents are employed in the Northeast (Table 4.4). Black respondents are nearly twice as likely their white peers to be employed in the South. In contrast, white respondents were more likely than their black peers to be employed in the Midwest and West. These patterns are not surprising given the strong concentration of black respondents employed in historically black colleges and universities (most of which are located in the South. 

Equal percentages (either 100% or lower) of all sample components pass through both columns and eventually reach the detector. 

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