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What Is a Safety Valve? Structure, Working Principle & Detailed Classification

03/05/2026

WHAT IS A SAFETY VALVE? STRUCTURE, WORKING PRINCIPLE AND DETAILED CLASSIFICATION

WHAT IS A SAFETY VALVE?

A Safety Valve is a mechanical device designed to automatically release excess pressure in a system when the pressure exceeds a preset limit.

👉 When system pressure rises above the setpoint → the valve opens automatically → releases fluid → reduces pressure → protects equipment and personnel.

Safety valves are mandatory in systems such as:

Steam boilers
Pressure vessels
Compressed air systems
Oil & gas systems
Chemical processing plants
Industrial factories

SAFETY VALVE STRUCTURE

A typical safety valve consists of the following main components:

1. Body

Main pressure-retaining shell
Materials: cast iron, carbon steel, stainless steel (SS304, SS316)
Connection: threaded or flanged

2. Disc

The key sealing element
Contacts the seat to stop flow

3. Spring

Provides closing force
Adjustable to set opening pressure

4. Stem

Transfers force between spring and disc

5. Seat

Ensures tight sealing
Materials: metal or PTFE

6. Bonnet

Protects internal components

7. Adjusting Screw

Used to set the valve opening pressure

WORKING PRINCIPLE OF A SAFETY VALVE

The operation is based on the balance between system pressure and spring force:

Normal condition:

Pressure < set pressure
Spring keeps the disc tightly closed
Valve remains fully shut

Overpressure condition:

Pressure > spring force
Disc lifts
Valve opens and discharges fluid

Pressure recovery:

Pressure returns to safe level
Spring pushes disc back
Valve closes

👉 This is a fully automatic mechanism, requiring no external control.

TYPES OF SAFETY VALVES

1. Based on operating principle

a. Spring Loaded Safety Valve

Most common type
Operates using spring force
Suitable for steam, gas, liquid

b. Lever Safety Valve

Uses a weighted lever
Less common
Typically for low-pressure systems

c. Pilot Operated Safety Valve

Controlled by a pilot valve
High accuracy
Suitable for high-pressure systems

2. Based on application (VERY IMPORTANT)

🔥 Safety valves for steam (Steam Service)

Type: Pop Safety Valve
Feature: rapid full opening
Materials: carbon steel / stainless steel
Application: boilers

👉 Essential for boiler systems

💧 Safety valves for water (Liquid Service)

Type: Relief Valve
Feature: gradual opening
Application: water systems, HVAC, fire protection

⛽ Safety valves for oil & fuel

Materials: SS316 / carbon steel
Seat: metal or PTFE
Requirement: high tightness, explosion safety

💨 Safety valves for compressed air

Type: safety or relief valve
Typical pressure: 6–10 bar
Application: air compressors, tanks

☣️ Safety valves for chemicals

Materials: SS316, PTFE-lined
Corrosion-resistant
Used in chemical industries

3. Based on connection

Threaded safety valve
Flanged safety valve
Welded safety valve

4. Based on pressure rating

PN10 / PN16 / PN25 / PN40
Class 150 / 300 / 600 / 900

DIFFERENCE BETWEEN SAFETY VALVE AND RELIEF VALVE

Criteria	Safety Valve	Relief Valve
Medium	Gas / Steam	Liquid
Opening	Sudden (pop action)	Gradual
Application	Boilers	Water, oil systems

ADVANTAGES OF SAFETY VALVES

✔ Protects system from overpressure
✔ Fully automatic operation
✔ High reliability
✔ Fast response
✔ Prevents explosion risks

DISADVANTAGES

❌ Requires periodic inspection
❌ May clog in dirty media
❌ Spring fatigue can affect accuracy

INDUSTRIAL APPLICATIONS

Safety valves are widely used in:

Steam boilers
Power plants
Compressed air systems
Oil & gas industry
Chemical plants
Food & pharmaceutical industries
HVAC systems
Pressure vessels

HOW TO SELECT A SUITABLE SAFETY VALVE

1. Based on medium

Steam → carbon steel / stainless steel safety valve
Water → relief valve
Air → safety valve
Chemicals → SS316 + PTFE

2. Based on working pressure

Set pressure slightly above operating pressure (~10–15%)

3. Based on material

SS304: clean water
SS316: chemicals / seawater
Carbon steel: steam

4. Based on standards

ASME
API 526 / API 527
DIN / JIS

CONTACT PHUC MINH ENGINEERING

Phuc Minh Engineering Co., Ltd specializes in supplying:

Spring-loaded safety valves
Steam safety valves
Air safety valves
Chemical safety valves
Flanged and threaded safety valves

🌐 Website: pm-e.vn
📧 Email: info@pm-e.vn
📱 Hotline: +84 907 450 506 – +84 902 720 814 – +84 979 737 351 – +84 902 800 728

CONCLUSION

Safety valves are critical components in any pressurized system. Selecting the correct type based on medium (steam, liquid, gas, chemicals) ensures:

✔ System safety
✔ Prevention of dangerous overpressure incidents
✔ Longer equipment lifespan
✔ Reduced maintenance costs

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