What must be installed in piping sections to relieve pressure from trapped liquid LP-Gas?

The correct answer is the hydrostatic relief valve. This type of valve is specifically designed to alleviate pressure buildup that can occur when liquid propane gas is trapped within the piping. When LP-Gas is subjected to temperature increases, it can expand and create dangerous levels of pressure. The hydrostatic relief valve automatically opens at a preset pressure, allowing excess liquid gas to escape safely, thus preventing potential rupture or failure of the piping system.

In contrast, an emergency shutoff valve is meant to completely shut down the flow of gas in case of an emergency but does not serve the function of relieving trapped pressure. A pressure gauge is useful for monitoring the pressure in the system, but it does not actively relieve any pressure. A gas meter is designed to measure the amount of gas being used but does not play a role in managing pressure within the piping system. Thus, the hydrostatic relief valve is essential for safety in handling liquid LP-Gas by preventing hazardous pressure conditions.