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