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

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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

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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.

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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

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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

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💧 Safety valves for water (Liquid Service)

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

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⛽ Safety valves for oil & fuel

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

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💨 Safety valves for compressed air

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

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☣️ Safety valves for chemicals

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

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3. Based on connection

• Threaded safety valve
• Flanged safety valve
• Welded safety valve

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4. Based on pressure rating

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

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DIFFERENCE BETWEEN SAFETY VALVE AND RELIEF VALVE

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ADVANTAGES OF SAFETY VALVES

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

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DISADVANTAGES

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

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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

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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

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2. Based on working pressure

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

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3. Based on material

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

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4. Based on standards

• ASME
• API 526 / API 527
• DIN / JIS

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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

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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