How Does a Safety Valve Work?

The working principle is based on the balance of pressure and spring force. When the pressure in the system is below the set pressure value, the spring force keeps the disc closed and the fluid is not discharged. If the pressure exceeds the set pressure level, the pressure force overcomes the spring, the disc lifts and the fluid is discharged. At this time, the pressure starts to drop. When the pressure drops back to a safe level, the spring closes the disc again and the system returns to normal.

What is a Safety Valve (Relief Valve)?

A relief valve is a safety element that reduces pressure and protects equipment by discharging fluid when the pressure in a system exceeds a specified safe level. It is mainly used in pressure-generating equipment such as pumps, pressure vessels, pipelines, compressors, and hydraulic systems.

It protects the system from explosion, leakage, equipment damage and personnel safety risks.

Why Use It?

A relief valve is vital in the following situations:

Risk

Role of the Relief Valve

Equipment may be damaged if the pressure rises uncontrollably

Discharges excess pressure

Pump dead heading

Protects the pump from overloading

Pressure increase due to thermal expansion

Reduces pressure to a safe level

Sudden pressure surges in the installation

Ensures system safety

Human and environmental safety

Prevents accidents

A pressurized system without a relief valve poses a serious hazard.

Structure (Basic Components)

A relief valve usually consists of the following parts:

  • Valve body
  • Inlet and outlet connections
  • Piston or disc (part that sits on the valve seat)
  • Spring → Maintains the set pressure
  • Set screw → Determines the operating pressure
  • Cover and guiding system

Thanks to the tight closing of the disc with the spring on the valve seat, there is no flow passage during normal operation.

How Does It Work?

The working principle is based on the balance of pressure and spring force:

  1. When the pressure in the system is below the set pressure value:
    • The spring force keeps the disc closed
    • Fluid is not discharged
  2. If the pressure exceeds the set pressure level:
    • The pressure force overcomes the spring
    • The disc lifts and fluid is discharged
    • Pressure starts to drop
  3. When the pressure drops back to a safe level:
    • The spring closes the disc again
    • The system returns to normal

These processes take place very quickly and provide continuous control.

Relief Valve Types

Type

Usage Feature

Spring-loaded

The most common type, in pumps and hydraulic systems

Pilot-operated

High flow rate and precise pressure control

Thermal relief

Only for thermal expansion pressure

Vacuum relief

Protects against negative pressure

Safety Valve (PSV)

With sudden opening and closing in pressure vessels

Selection Criteria

The following parameters should be considered when selecting a relief valve:

  • Set pressure (safety pressure)
  • Min./Max. operating pressure
  • Fluid type (corrosive, viscous, gas, steam)
  • Discharge flow rate
  • Material selection (SS, bronze, cast iron, PTFE gasket, etc.)
  • Standard requirements such as ATEX, API, ASME