What is a key feature of a temperature and pressure relief valve?

A temperature and pressure relief (TPR) valve is designed to protect a water heater from potentially dangerous conditions caused by excess temperature or pressure. One of its key features is that it must have a relief capacity that is not less than the heat input of the water heater. This requirement ensures that, in the event of overly high temperature or pressure, the valve will be able to release sufficient water to prevent the tank from rupturing or causing an explosion.

Correctly sizing the valve with respect to the heat input ensures effective emergency action when the operational limits are exceeded. If the relief capacity were less than the heat input, the valve might not effectively manage the situation, leaving the system vulnerable to catastrophic failure.

The other options either do not adequately address the critical safety function of the valve or present misconceptions about its requirements. The thermal tolerance of a TPR valve is indeed important, but what's pivotal is its ability to handle the specific heat input. The necessity of a discharge pipe relates to the safe direction of released water, while the requirement for regular manual operation is not a standard practice for TPR valves. They are designed to operate automatically when conditions necessitate their function.