page_title: Safety valve
section_title: Direct spring valves
hierarchical_section_title: Safety valve / Development of the safety valve / Direct spring valves
caption_attribution_description: A working replica of Robert Stephenson's's 1830 locomotive Planet which ran on the Liverpool and Manchester Railway. Seen here at the Manchester Science Museum.
context_page_description: A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve, which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits. Pilot-operated relief valves are a specialized type of pressure safety valve. A leak tight, lower cost, single emergency use option would be a rupture disk.
  Safety valves were first developed for use on steam boilers during the Industrial Revolution. Early boilers operating without them were prone to explosion unless carefully operated.
  Vacuum safety valves are used to prevent a tank from collapsing while it is being emptied, or when cold rinse water is used after hot CIP or SIP procedures.
  When sizing a vacuum safety valve, the calculation method is not defined in any norm, particularly in the hot CIP / cold water scenario, but some manufacturers have developed sizing simulations.
context_section_description: 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.
caption: Locomotive Planet (1830), with a brass-cased direct spring valve
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