(4)Safety devices. - Every pressure vessel shall be fitted with-(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 need be set to operate at the maximum permissible working pressure and the additional device shall be set to discharge at a pressure not more than 5 per cent in excess of the maximum permissible working pressure;(b)a suitable pressure guage with dial range not less than 1.5 times the maximum permissible working pressure, easily visible and designed to show at all times the correct internal pressure and marked with a prominent red mark at the maximum permissible working pressure of the pressure vessel;(c)a suitable nipple and globe valve connected for the exclusive purpose of attaching a test pressure guage for checking the accuracy of the pressure gauge referred to in clause (b) of this sub-rule;(d)a suitable stop valve or valves by which the pressure vessel may be isolated from other pressure vessels or plant or source of supply or pressure. Such a stop valve or valves shall be located as close to the pressure vessel as possible and shall be easily accessible; and(e)a suitable drain cock or valve at the lowest part of the pressure vessel for the discharge of the liquid or other substances that may collect in the pressure vessel:Provided that it shall be sufficient for the purpose of this sub-rule if the safety valve or pressure relieving device, the pressure gauge and the stop valve are mounted on a pipe line immediately adjacent to the pressure vessel and where there is a range of two or more similar pressure vessels served by the same pressure load only one set of such mountings need be fitted on the pressure load immediately adjacent to the range of pressure vessels, provided they cannot be isolated.
