Safety Relief Valve Weighted valves were sensitive to bouncing from the rough riding of early locomotives. One solution was to use a lightweight spring rather than a weight. This was the invention of Timothy Hackworth on his Royal George of 1828.Owing to the limited metallurgy of the period, Hackworth's first spring valves used an accordion-like stack of multiple leaf springs. These direct-acting spring valves could be adjusted by tightening the nuts retaining the spring. To avoid tampering, they were often shrouded in tall brass casings which also vented the steam away from the locomotive crew.