Safety valve principle

What is the principle of safety valve?

  • The safety or safety relief valve is the primary type of device used to prevent overpressure in industry.
  • When a specific maximum pressure is reached, the safety valve opens, safely decreasing the excess pressure by releasing a volume of fluid from within the plant.
  • A safety valve is a critical component used in various industrial applications to protect equipment and systems from excessive pressure. 
  • Its primary function is to release excess pressure by opening when the pressure exceeds a predetermined set point, thereby preventing catastrophic failures or explosions.

What is the construction of safety valve in boiler?

The safety valve is composed mostly of three components: a nozzle, disc, and spring. Through the nozzle, pressurised steam enters the valve and is then threaded to the boiler. The disc serves as the nozzle’s lid, opening or shutting in response to pressure from the boiler. The amount of pressure can be adjusted by modifying the spring’s tension.

Construction of a safety valve

Safety valve principle 1
  • The construction of a safety valve typically consists of several key components. The valve body is the main housing that contains all the internal parts and connections. 
  • It is usually made from durable materials such as cast steel or stainless steel to withstand high pressures and temperatures.
  • The valve seat is a crucial part that provides a tight seal when the valve is closed. 
  • It is typically made from materials such as stainless steel or brass and is designed to resist wear and corrosion. 
  • The valve disc or plug is the component that moves up and down to control the flow of fluid. 
  • It is usually made from materials that can handle high temperatures and pressures, such as stainless steel or hardened alloys.
  • To ensure proper functioning, safety valves often include a spring mechanism. The spring applies a force on the valve disc or plug, keeping it closed until the pressure exceeds the set point. 
  • Once the pressure surpasses the set point, the force of the spring is overcome, and the valve opens, allowing the excess pressure to be released.
  • Safety valves also have an adjustment mechanism that allows for setting the desired pressure at which the valve should open. 
  • This can be achieved through adjusting the tension of the spring or using additional components like a lever or weight system.
  • The construction of a safety valve involves robust materials, precise engineering, and reliable mechanisms to ensure the valve operates effectively and provides essential protection against overpressure situations.

What are the components of a safety valve?

Key components of the construction of a safety valve

  • The device is composed of a cast iron body with two branch pipes.
  • Over the valve seat, two distinct valves are positioned.
  • Two pivots are used to position a lever over the valve.
  • A spring ensures that the lever remains firmly in place.
  • One end of the spring is attached to the lever, while the other end is attached to the valve body.
  • With the aid of spring force, the valve is maintained in place.
  • In addition to the main components, safety valves may incorporate features such as a bonnet, which provides protection and insulation, and a blowdown ring, which helps to control the release of pressure when the valve opens.

What is the working principle of safety valve?

Safety valve principle 2
  • The safety valve is initially closed, with a spring or other mechanical force holding the valve disc or plug tightly against the valve seat.
  • When the pressure inside the system or equipment reaches a predefined set point, it overcomes the spring’s force, forcing the valve upwards off the seat.
  • The opening formed by the valve’s raising allows excess pressure to be discharged from the system.
  • The pressurized fluid or gas goes out to a safe location, such as an exhaust pipe or a designated outlet, after passing through the safety valve.
  • When the pressure drops below the set point, the spring or mechanical force continues to apply a downward push on the valve disc, allowing it to close.
  • The reseating of the valve restores the seal, stopping any additional fluid or gas discharge.
  • The safety valve functions as a fail-safe mechanism, ensuring that pressure release happens when the pressure exceeds the set point, hence preventing system or equipment damage or failure.
  • Regular maintenance and testing are required to ensure the safety valve’s correct operation and reliability in protecting against overpressure conditions.
  • Safety valves have been designed to be repeatable and reliable, offering an important precaution against excessive pressure in a variety of industrial applications.

The following describes the functions of the various sections of the safety valve:

  1. The function of the Nozzle is that of the Pressure Entrance 
  1. Disc serves the role of Lid.
  1. The role of the spring is that of a pressure controller.

What are the different types of safety valves?

Categories of safety valves

There are three different categories of safety valves 

  • Spring loaded pressure relief valves
  • Pilot-operated Pressure-relief Valves
  • Dead-Weight Pressure-relief Valves

What is spring loaded pressure relief valve?

Spring-loaded Pressure-relief Valves

Safety valve principle 3
  • Typically, when we talk about safety valves, we’re talking about the most popular kind Spring-loaded Pressure-Relief valves.
  • The “Disc” is intended to be pressed against the inlet pressure by the spring’s load. 
  • Depending on the fluid type steam, gas, or liquid a bellows model is offered to remove the back pressure consequences.

What is a pilot operated relief valve?

Pilot-operated Pressure-relief Valves

Safety valve principle 4
  • The main valve and pilot assembly make up pilot-operated pressure-relief valves. 
  • Although spring-loaded pressure-relief valves use the force of the spring to overcome the inlet pressure, pilot-operated pressure-relief valves use a pilot assembly to control the reliving and reseating pressure, which functions almost identically to spring-loaded pressure-relief valves. The Main Valve does not have an adjustable feature.
  • Pilot-operated pressure-relief valves, which are used in harsh conditions like high pressure, have larger size variations than spring-loaded kind.

What is a deadweight safety valve?

Dead-Weight Pressure-relief Valves

Safety valve principle 5
  • Dead-weight pressure-relief valves only change relieving pressure by the disc weight in the event that the design pressure of the pressure vessel is set at a very low pressure. 
  • When the internal pressure of a pressure vessel decreases to a negative pressure, the vacuum relief valve has been using this functional characteristic to absorb the pressure.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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