PENN Controls Products Catalog

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b. To approximate the valve opening pressure (P OPEN ), add an approximate of 10 psi (0.7 bar) to the valve closing pressure. Note: Add an approximate of 20 psi (1.4 bar for 3/8in. valves. Figure 97: Valve opening pressure c. From the pressure-temperature chart for the selected refrigerant, read the refrigerant condensing pressure (P COND ) , also known as operating head pressure, corresponding to the selected condensing temperature. d. Subtract the valve opening pressure from the refrigerant condensing pressure. This calculation gives the head pressure rise. Figure 98: Refrigerant head pressure rise 3. Use the following steps to determine the available water pressure to the valve (P AVAIL ). This is the actual water pressure available to force water through the valve. a. Determine the inlet pressure (P IN ). This is the water pressure from city water mains, pumps, or other sources. b. Pressure drop through condenser (ΔP COND ) is the difference in water pressure between the condenser inlet and the condenser outlet. Obtain this information from the condenser manufacturer. c. Estimate or calculate the pressure drop through all associated piping (P LOSS ). d. Subtract ΔP COND and P LOSS from P IN . The result is P AVAIL . Figure 99: Available water pressure 4. Select the correct valve size from the flowcharts by locating a point on a chart that satisfies the flow, the head pressure rise above opening point, and the pressure drop across the valve. Metric conversions Use these equations to convert between U.S. and S.I. units. • 1 dm 3 /s = 3.6 m 3 /h = 15.9 U.S. gal. /min. = 13.2 U.K. gal. /min. • 1 bar = 100 kPa = 0.1 MPa = 1.02 kg/cm 2 = 0.987 atm = 14.5 psi V246 flowcharts The maximum recommended differential water pressure across a valve is 60 psig (4.1 bar). 267 Refrigeration Products Catalog

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