WHAT IS A PRESSURE REDUCING VALVE (PRV)? STRUCTURE, WORKING PRINCIPLE AND DETAILED CLASSIFICATION

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WHAT IS A PRESSURE REDUCING VALVE?

A Pressure Reducing Valve (PRV) is a device used to reduce high inlet pressure to a lower, stable outlet pressure, ensuring safe and efficient system operation.

👉 The valve operates automatically, without the need for electricity or external control.

👉 When inlet pressure fluctuates → the valve self-adjusts → maintains constant downstream pressure.

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ROLE OF PRESSURE REDUCING VALVES IN SYSTEMS

PRVs are used to:

• Reduce excessive supply pressure
• Maintain stable downstream pressure
• Protect equipment (pumps, gauges, valves)
• Prevent pipe rupture and leakage
• Improve energy efficiency

👉 Without a PRV, excessive pressure can damage pipelines and system components.

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STRUCTURE OF A PRESSURE REDUCING VALVE

A typical PRV consists of the following components:

1. Body

• Main pressure-retaining housing
• Materials: cast iron, carbon steel, stainless steel (SS304, SS316)

2. Disc / Plug

• Regulates flow
• Controls pressure reduction

3. Spring

• Provides adjustable set pressure

4. Diaphragm or Piston

• Senses downstream pressure
• Controls valve movement

5. Stem

• Transfers force to the disc

6. Seat

• Ensures tight sealing

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WORKING PRINCIPLE OF A PRV

The valve operates based on force balance between spring force and downstream pressure:

Normal condition:

• Outlet pressure equals set pressure
• Valve modulates opening to maintain stability

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When outlet pressure decreases:

• Spring force becomes dominant
• Valve opens further
• Flow increases → pressure rises

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When outlet pressure increases:

• Downstream pressure exceeds spring force
• Valve closes partially
• Flow reduces → pressure drops

👉 Result: stable and constant outlet pressure, regardless of inlet pressure variations.

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TYPES OF PRESSURE REDUCING VALVES

1. Based on operating principle

a. Direct Acting PRV

• Uses spring and diaphragm
• Simple design
• Cost-effective

👉 Suitable for small systems (water, air)

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b. Pilot Operated PRV

• Uses a pilot control valve
• High accuracy and stability

👉 Suitable for large systems, especially steam applications

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CLASSIFICATION BY APPLICATION (VERY IMPORTANT)

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🔥 1. PRV for Steam

• Type: steam pressure reducing valve
• Mechanism: diaphragm or pilot operated
• Materials: carbon steel / stainless steel
• Application: boilers, steam systems

👉 Essential for maintaining stable steam pressure

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💧 2. PRV for Water

• Type: direct acting or diaphragm type
• Materials: brass, cast iron, stainless steel
• Application: water supply, HVAC

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💨 3. PRV for Compressed Air

• Type: air regulator / PRV
• Typical pressure: 6–10 bar
• Application: air compressors, pneumatic systems

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⛽ 4. PRV for Oil & Fuel

• Materials: SS316 / carbon steel
• Requirements: tight sealing, fire safety

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☣️ 5. PRV for Chemicals

• Materials: SS316, PTFE-lined
• High corrosion resistance

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DIFFERENCE BETWEEN PRV AND SAFETY VALVE

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ADVANTAGES OF PRVs

✔ Maintain stable pressure
✔ Fully automatic operation
✔ Protect system components
✔ Improve energy efficiency
✔ Reduce vibration and noise

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DISADVANTAGES

❌ Requires proper sizing
❌ Sensitive to dirt and debris
❌ Spring wear affects accuracy

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INDUSTRIAL APPLICATIONS

PRVs are widely used in:

• Steam systems
• Water supply systems
• Compressed air systems
• Oil & gas industry
• Chemical plants
• Food & beverage industry
• HVAC systems

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HOW TO SELECT A SUITABLE PRV

1. Based on medium

• Steam → steam PRV
• Water → diaphragm PRV
• Air → regulator
• Chemicals → SS316

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2. Based on pressure

• Select appropriate inlet & outlet pressure
• Avoid oversizing or undersizing

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3. Based on flow rate

• Determine required flow capacity
• Select correct valve size (DN)

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4. Based on standards

• DIN / JIS / ANSI
• API

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CONTACT PHUC MINH ENGINEERING

Phuc Minh Engineering Co., Ltd specializes in supplying:

• Steam pressure reducing valves
• Water PRVs
• Air pressure regulators
• Chemical PRVs
• Control pressure 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

Pressure Reducing Valves are essential components in modern industrial systems:

✔ Maintain stable pressure
✔ Protect equipment
✔ Extend system lifespan
✔ Reduce operating costs