Which of the following is NOT a common pumping arrangement for condensate return?

The correct answer is hydraulic, as it is not typically classified as a common arrangement for condensate return in HVAC systems. Instead, condensate return is most commonly achieved through gravity, pressure differential, or electric pumping setups.

Gravity systems rely on the natural force of gravity to move condensate from low points to drainage points, making them simple and energy-efficient for short distances. Pressure differential systems utilize differences in pressure to facilitate condensate flow, often using traps and other components to maintain proper pressure and flow dynamics.

Electric pumps, while they require power, are another prevalent method to manage condensate return, especially in situations where gravity is insufficient or when condensate needs to be pumped upward against gravity.

Hydraulic arrangements, on the other hand, are less commonly associated with condensate return because they usually refer to systems that utilize pressurized liquids to transmit power or perform work, not specifically for the return of condensate. Hence, this option stands out as not fitting the typical pumping solutions used in condensate return processes.