What must occur before a hydraulic pressure reading can be shown on the gauge after an accumulator installation?

The correct answer is that the fluid side of the accumulator must be charged before a hydraulic pressure reading can be shown on the gauge. This is because an accumulator functions by storing energy in the form of pressurized fluid. When the fluid side is charged, it allows the system to generate hydraulic pressure, which subsequently can be measured by the pressure gauge. Without this initial charging, there would be no fluid pressure in the accumulator, and therefore no reading would be available on the gauge.

In hydraulic systems, it is essential that the accumulator is filled with fluid because it enables proper functioning as a pressure stabilizer and energy storage device. A lack of fluid would mean that the accumulator cannot perform its intended role within the hydraulic circuit.