Safety valve is a valve that works automatically to release the excessive pressure. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits. Safety Valve is mainly installed in a chemical plant, electric power boiler, gas storage tank, preventing the pressure vessels from exploding or damaging.

safety_valve

Characteristics & operation of safety valve

  • Safety valves are also known as Pressure Relief Valves.
  • They are mainly of two types –
    • Spring Loaded Safety Valves
    • Pilot Loaded Safety Valves
  • The purpose of its existence is to ensure the safety of Life and Pressurized equipment (e.g. Boiler). For a Safety Valve, continuous operation under any condition, is highly desirable.
  • This valve must never be confused as any kind of regulatory valve. As it does not regulate the flow of fluid (particularly steam), it only helps in maintaining the pressure within the Boiler by the venting out the Steam as the latter goes up the safety limit.
  • Another important point to be considered is that, two Safety valves are mounted on the Steam Drum. And both of them are installed at a different pressure.
  • Let us suppose, for a Steam Boiler of 1 TPH capacity and 10.54kg/cm2 (150 PSI) working pressure. Two Safety valves of same size are mounted on the Steam Drum , one at 11 kg/cm2 and the other at 11.5kg/cm2.

Also read – Why Do We Need Safety Valve in Boiler?

This pressure difference has two advantages –

  1. Both safety valves if set at same temp. Then at the time of high pressure rise in Steam Boiler both of them will open up and release Steam, leading to high steam quantity loss.
  2. When steam pressure goes up even after automatic opening up of first Safety Valve, the second Safety valve opens up to reduce the Steam Drum pressure.
  • The operating principle of Safety Valve is such that it is mounted at the top of Steam Drum and its disc rests at the bottom applying a downward static pressure greater than the working pressure of the Steam drum. But as the pressure rises in the Steam Drum, the steam applies the upward pressure and lifts up the disc, at the disc reaches the maximum height. The outlet valve gets opened and the steam gets released to the atmosphere through this opening.
  • Sizing of both the Safety valves must be such that the overall flow through both the valves must be more than the steam flow through the Boiler outlet connection.
  • It only works when the pressure inside the steam drum rises above the set limit.
  • Some of the common problems encountered during Safety Valve operation are damage of Seat & Disc, Corrosion, and presence of foreign Particles, Simmering, Porous Gasket and Loosened Nuts Bolts due to Vibrations.

 

We at Thermodyne, provide the Full Lift Spring Loaded Safety Valve to ensure maximum safety of Boiler Operation.

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