Ros 'pop' safety valve, c 1904. This is a

Ros 'pop' safety valve, c 1904. This is a sectioned example of the pop safety valve patented by R L Ros in 1902 and 1904. At the top of the surrounding casing, beside the main valve, there is a cap on which the escaping steam exerts sufficient presure to relieve the valve spring, so permitting the valve to open wide and give a free escape of steam.