A safety valve is a valve that functions as a protective equipment from the process of explosion or damage, which is mainly installed in pressure vessels such as chemical plants, electric kettles, and gas storage tanks.

The Safety Valve is also a type of valve that automatically acts when the valve inlet pressure rises to a predetermined pressure, to open valve discs and remove liquids (steam or gas); and when the pressure drops to the specified value, to close the valve disc again. The safety valve is referred to as a final safety device that controls pressure and releases a certain amount of liquid by itself without the support of electrical power.

The safety valve also supports energy industry safety and also safety, security of our lives.
For a more complete explanation the function of the safety valve is:

1. The "Nozzle" in the Safety Valve starts to receive pressure higher than the inlet valve side.
2. When the pressure becomes higher than the set pressure, "Disc" starts to lift and remove the liquid.
3. When the pressure decreases to a predetermined pressure, the spring forces close the "Disc".
• (Role of spare parts)
• Nozzle --- Pressure Entrance
• Disc ----- Lid
• Spring --- Pressure Controller
Clasification Of Safety Valve

 

Generally, the safety valves are referred to the Spring-loaded Pressure-relief valves, the most common type ( See the left figure ).

 

Pilot-operated Pressure-relief Valves are composed of Pilot Assy and Main Valve. Although Spring-loaded Pressure-relief valves adopts the force of the spring against the inlet pressure, the reliving pressure and reseating pressure of the Pilot-operated Pressure-relief Valves is controlled by Pilot Assy, which acts nearly as same as Spring-loaded Pressure-relief valves. There is no adjusting function in the Main Valve.

 

In case the design pressure of the pressure vessel is set at very low pressure, Dead-weight Pressure-relief valve adjusts relieving pressure only by the disc weight.

SAFETY VALVE OPERATION

Safety Valves used within the Building Services Industry follow a design that uses an applied force (a spring) to directly oppose the system force.

This valve design utilises three states;

  1. Equilibrium
    • The equilibrium state is where the closing forces, ie applied by the spring and any back pressure, is in ‘equilibrium’ (balanced) with the opening forces, ie applied by the system pressure.  The disc and seat are ‘just’ in contact so flow has not started but about to start
 
  1. Fully open
    • The fully open state is where the valve can pass the maximum capacity at the specified overpressure.  It follows of course, that for the valves to open, the system force must exceed the equilibrium force, ie overcome the applied spring and back pressure force.
      Some designs of Safety Valve, like the NABIC Figure 500, achieve a higher discharge flow rate by having a higher disc lift and larger discharge size
 
  1. Fully closed
    • The fully closed state is where the valves is fully closed, ie nil leakage.  The closing force exceeds the opening force, ie the opening force is lower than the equilibrium force
 
 

Safety Valve Application

Safety valves issue excess amounts of air, water or steam from water tanks or piping systems such as heaters - hot domestic water - and solar heating systems.

Connection to solar heating / heating systems
The safety valve must be installed above the boiler or heat exchanger. There should be no isolation ball valve or reduction in the area between the safety valve and other heat / heat exchangers. The discharge pipe (at least 15 mm internal diameter) of the safety valve must end with a drain with an open and visible release hole.

Connection to domestic water
Safety valves for hot domestic water must be installed in cold water pipes for hot water tank heat exchangers. There should be no isolation ball valve or reduction in the area between the safety valve and other heat / heat exchangers. The drain pipe from the safety valve must end in the drain with an open and visible drain hole.

Inspection and drying
Turn the handle to the first notch, and the valve fully opens. Valves can be checked, and the system can be drained from water through a safety valve. Rotate and the valve acts as a normal safety valve.