Which item is installed on propane cylinders to allow excess pressure to escape?

A relief valve is specifically designed to allow excess pressure to escape from propane cylinders. It functions as a safety mechanism to prevent dangerous over-pressurization. When the pressure inside the cylinder exceeds a preset limit, the relief valve opens automatically, allowing gas to vent safely until the pressure returns to normal levels. This helps to avert potential hazards such as explosions or ruptures of the cylinder.

In the context of propane cylinders, ensuring that the pressure is maintained within safe limits is critical for safe handling and operation. The relief valve is calibrated for specific pressure ranges according to safety regulations, ensuring that it operates effectively to protect both the cylinder and users.

Other components mentioned, such as frangible plugs, blowout disks, and purge valves, serve different purposes and are not specifically designed for the same function as the relief valve in mitigating pressure buildup.