The pressure relief valve is typically installed on the boiler or reasonably close to the boiler outlet with:

A pressure relief valve is a critical safety device designed to prevent excessive pressure from building up in a boiler, which could lead to dangerous conditions or even catastrophic failure. It is important for the pressure relief valve to be installed directly on the boiler or as close as possible to the boiler outlet without any intervening valves. This positioning is crucial because it allows the relief valve to immediately and effectively respond to any pressure increase within the system.

When the pressure rises above the set pressure of the valve, the valve must open quickly to release steam or water, bringing the pressure back down to a safe level. If there were any other valves (such as a manual shutoff valve) installed between the boiler and the relief valve, there is a risk that these valves could inadvertently remain closed during an over-pressure event, preventing the relief valve from functioning properly, which would compromise safety.

Therefore, ensuring that there is no obstruction, such as a shutoff valve, between the boiler and the relief valve is paramount for the effective operation and safety of the boiler system. This installation practice guarantees that the pressure relief valve can do its job without impediment when it is needed most.