A constant pressure range is maintained in the potable water system of many vessels by using __________.

Correct Answer: Option C — an air-cushion in the hydro-pneumatic tank

Hydro-pneumatic tanks utilize an air cushion to maintain constant pressure in potable water systems. As the pump fills the tank, the air is compressed. This compressed air acts as a spring, providing a steady discharge pressure and preventing the pump from cycling on and off too frequently.