What is the operating force on a water regulating valve installed in a water-cooled condenser?

The correct choice for the operating force on a water regulating valve installed in a water-cooled condenser is high side pressure. This is because the water regulating valve is designed to maintain the proper flow of water through the condenser, which is crucial for effective heat exchange.

In a water-cooled condenser, the refrigerant or gas typically operates under high pressure on the high side of the system. As this high-pressure refrigerant is condensed, the regulating valve operates by responding to the pressure changes in the system. Therefore, the high side pressure directly influences the valve's operation, ensuring that the flow of cooling water is adjusted based on the thermal load requirements in order to maintain efficient operation of the condenser.

Other forces, such as low side pressure or variable pressure, would not serve as the primary operating mechanism for the valve in this context. A constant temperature does not directly exert force on the valve either; instead, it is the pressure differential created by the high side that effectively modulates the valve's opening and thus regulates water flow.