Section 56(4)(a) in The West Bengal Factories Rules, 1958
(a)a suitable safety valve or other effective pressure relieving device of adequate capacity to ensure that the maximum permissible working pressure of the pressure vessel shall not be exceeded. It shall be set to operate at a pressure not exceeding the maximum permissible working pressure and when more than one protective device is provided, only one of the devices used be set to operate at the maximum permissible working pressure and the additional device shall be set to discharge at a pressure not more that 5 per cent in excess of the maximum permissible working pressure;