The machinery systems on board ship consist of several safety features for safe and smooth operation of the ship and also for the safety of its personnel. Relief valve is one such important safety device which is used in almost all the machinery systems which deal with extremely high pressures. These high pressures often tend to go over the predetermined limits and the over pressure thus created is the pressure just above the maximum allowable working pressure (MAWP) or designed working pressure.

There are systems onboard a ship which are operated by pneumatics or hydraulics and sometimes even air or electronics. For this reason, the relief valve by construction and operation should be such that even in case of failure of the control system, relief valve must lift to safeguard the system from over pressurized