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What Is a Pressure Reducing Valve (PRV)? Structure, Working Principle & Types

03/05/2026

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

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.

What Is a Pressure Reducing Valve (PRV)? Structure, Working Principle & Types

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.

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

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

When outlet pressure decreases:

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

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.

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)

b. Pilot Operated PRV

Uses a pilot control valve
High accuracy and stability

👉 Suitable for large systems, especially steam applications

CLASSIFICATION BY APPLICATION (VERY IMPORTANT)

🔥 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

💧 2. PRV for Water

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

💨 3. PRV for Compressed Air

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

⛽ 4. PRV for Oil & Fuel

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

☣️ 5. PRV for Chemicals

Materials: SS316, PTFE-lined
High corrosion resistance

DIFFERENCE BETWEEN PRV AND SAFETY VALVE

Criteria	Pressure Reducing Valve (PRV)	Safety Valve
Function	Pressure regulation	Overpressure protection
Operation	Continuous	Emergency only
Application	Control systems	Safety systems

ADVANTAGES OF PRVs

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

DISADVANTAGES

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

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

HOW TO SELECT A SUITABLE PRV

1. Based on medium

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

2. Based on pressure

Select appropriate inlet & outlet pressure
Avoid oversizing or undersizing

3. Based on flow rate

Determine required flow capacity
Select correct valve size (DN)

4. Based on standards

DIN / JIS / ANSI
API

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

CONCLUSION

Pressure Reducing Valves are essential components in modern industrial systems:

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

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