Archive for January, 2011

Discharge-Bypass Valves Operation

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Discharge-Bypass Valves Operation

Discharge-bypass valves (DBV) respond to changes in downstream or suction pressure (see Fig. 11-37). When the evaporating pressure is above the valve setting, the valve remains closed. As the suction pressure drops below the valve setting, the valve responds and begins to open. As with all modulating-type valves, the size of the opening is proportional […]

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Discharge-Bypass Valves

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On many air-conditioning and refrigeration systems it is desirable to limit the minimum evaporating pressure. This is so especially during periods of low load either to prevent coil icing or to avoid operating the compressor at lower suction pressure than it was designed for. Various methods of operation have been designed to achieve the result—integral […]

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Nonadjustable ORO/ORD system operation

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Nonadjustable ORO/ORD system operation

The nonadjustable ORO head pressure-control valve and the ORD pressure-differential valve offer the most economical system of refrigerant side head-pressure control. Just as the ORI/ORD system simplified this type of control, the ORO/ORD system offers the capability of locating the condenser and receiver on the same elevation (see Fig. 11-36). By making these two valves […]

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Head-Pressure Control Valve Brazing procedures

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Any of the commonly used brazing alloys for high-side usage are satisfactory. It is very important that the internal parts be protected by wrapping the valve with a wet cloth to keep the body temperature below 250°F (121°C). Also, when using high-temperature solders, the torch tip should be large enough to avoid prolonged heating of […]

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ORD valve operation

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ORD valve operation

The ORD valve is a pressure differential valve. It responds to changes in the pressure difference across the valve (see Fig. 11-34). The valve designation stands for opens on rise of differential pressure. Therefore, the ORD is dependent on some other control valve or action for its operation. In this respect, it is used with […]

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ORO valve operation

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ORO valve operation

The ORO head pressure-control valve is an outlet pressure–regulating valve that responds to changes in receiver pressure. The valve designation stands for opens on rise of outlet pressure (see Fig. 11-33). The inlet and outlet pressures are exerted on the underside of the seat disc in an opening direction. Since the area of the port […]

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Head-Pressure Control Valves Operation

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Head-Pressure Control Valves Operation

The ORI head pressure-control valve is an inlet pressure regulating valve. It responds to changes in condensing pressure only. The valve designation stands for opens on rise of inlet pressure. As shown in Fig. 11-32, the outlet pressure is exerted on the underside of the bellows and on top of the seat disc. Since the […]

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Head-Pressure Control Valves

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Design of air-conditioning and refrigeration systems using air-cooled condensing units involves two main problems that must be solved if the system is to be operated reliably and economically. These problems are high-ambient and low-ambient operation. If the condensing unit is properly sized, it will operate satisfactorily during extreme-ambient temperatures. However, most units will be required […]

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OBIT valve test and operating pressures

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As with other pressure valves, it is possible to introduce nitrogen or carbon dioxide in an idle system to check for correct pressure settings. The usual precautions for working with gases apply here. The standard factory setting for the 0/50 psig range is 30 psi. For the 30/100 psig range, it is 60 psig. Since […]

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