Safety Valve vs. Relief Valve: What’s the Difference? (PRV, PSV, SRV Explained)

What is the difference between a safety valve and a relief valve?

The main difference between a safety valve and a relief valve is how they respond to overpressure.

A safety valve opens suddenly and fully at a defined set pressure to prevent catastrophic failure.
A relief valve opens gradually in proportion to rising pressure to control and stabilize system pressure.

Both are types of pressure relief valves (PRV, PSV, or SRV) and both require proper pressure relief valve testing to verify performance.

Pressure relief valve testing may also be referred to as in situ testing, leak testing, or valve calibration, depending on the method used or the aspect of performance being evaluated.

How This Relates to Pressure Relief Valve Testing

As outlined in pressure relief valve testing best practices, both safety valves and relief valves are tested to verify:

• Set pressure (often referred to as valve calibration)
  
• Opening behavior (pop action vs. proportional response)
  
• Seat integrity (commonly evaluated through leak testing)

In many cases, this testing is performed in situ (in-line), meaning the valve remains installed in the system during testing.

These terms—in situ testing, leak testing, and valve calibration—do not represent completely different tests.

They describe different perspectives of the same pressure relief valve testing process.

Pressure Relief Valve Terminology (Global Definitions)

In global industries, safety valves and relief valves fall under a broader category:

• PRV (Pressure Relief Valve): General umbrella term
  
• PSV (Pressure Safety Valve): Common in oil & gas and process industries
  
• SV (Safety Valve): Typically used in steam systems
  
• SRV (Safety Relief Valve): Combines both response types
  
• PRD (Pressure Relief Device): Includes valves and rupture disks

All of these require pressure relief valve testing—whether described as in situ testing, calibration, or leak verification—to ensure proper operation.

Quick Answer: Safety Valve vs. Relief Valve

The main difference between a safety valve and a relief valve is:

• A safety valve provides emergency protection and opens instantly at set pressure
  
• A relief valve regulates pressure and opens gradually as pressure increases

Both are pressure relief valves that require consistent testing, calibration, and verification of sealing performance

What Is a Pressure Relief Valve?

A pressure relief valve (PRV / PSV / SRV) is a mechanical device that releases excess pressure when a system exceeds its allowable limit.

Pressure relief valves are installed to:

• Prevent equipment damage
  
• Protect personnel
  
• Maintain safe operation
  
• Meet regulatory requirements (ASME, API, PED)

Pressure relief valve testing ensures:

• The valve opens at the correct set pressure (calibration)
  
• The valve reseals properly (leak performance)
  
• The valve operates correctly in service (in situ verification)

What Is a Safety Valve?

A safety valve (SV or PSV) is designed for emergency overpressure protection.

How a safety valve works:

• Remains closed until set pressure is reached
  
• Opens suddenly and completely (“pop action”)
  
• Releases full discharge capacity
  
• Reseats after pressure drops

Safety Valve Testing Considerations

When performing pressure relief valve testing on safety valves:

• Set pressure verification confirms proper pop action (calibration)
  
• Reseating performance confirms proper sealing (leak testing)
  
• Testing may be performed in situ to verify real operating conditions

All of these are part of the same pressure relief valve testing process.

What Is a Relief Valve?

A relief valve (PRV in liquid service) is designed for pressure control during normal operation.

How a relief valve works:

• Opens gradually near set pressure
  
• Modulates flow as pressure increases
  
• Maintains stable system pressure
  
• Closes when pressure normalizes

Relief Valve Testing Considerations

For relief valves, pressure relief valve testing focuses on:

• Set pressure accuracy (calibration)
  
• Proportional response behavior
  
• Sealing performance (leak testing)

Testing may also be performed in situ to evaluate performance under operating conditions.

Safety Valve vs. Relief Valve: Core Difference

The core difference between a safety valve and a relief valve is how they respond to pressure.

• A safety valve “pops” open instantly
  
• A relief valve opens gradually and proportionally

This difference directly affects:

• System design
  
• Valve selection
  
• How pressure relief valve testing results are interpreted

Safety Valve vs. Relief Valve Comparison Table

The following table summarizes the key differences between a safety valve and a relief valve:

How Pressure Relief Valve Testing Differs by Valve Type

Pressure relief valve testing follows the same overall process but evaluates different behaviors.

Safety valve testing (SV / PSV):

• Verify pop action at set pressure
  
• Confirm proper reseating (leak performance)
  
• Evaluate blowdown

Relief valve testing (PRV):

• Verify set pressure and modulation behavior
  
• Confirm stable operation
  
• Evaluate sealing performance (leak testing)

In both cases, calibration, leak verification, and in situ testing are part of the same testing framework—not separate tests.

Pressure Relief Valve Testing: Key Takeaways

• Safety valves and relief valves are both pressure relief valves (PRV, PSV, SRV)
  
• The key difference is how they open under pressure
  
• Pressure relief valve testing includes calibration, leak verification, and often in situ testing
  
• These terms describe different aspects of the same testing process, not separate procedures
  
• Proper testing ensures safety, compliance, and reliable system performance

FAQ: Safety Valve vs. Relief Valve

Do safety valves and relief valves require different tests?

No, safety valves and relief valves do not require different tests. Both use the same pressure relief valve testing process, but the results are evaluated differently based on valve behavior.

What is in situ pressure relief valve testing?

In situ testing refers to pressure relief valve testing performed while the valve remains installed in the system.

What is leak testing for a pressure relief valve?

Leak testing in pressure relief valves evaluates how well the valve reseals after opening and whether it maintains proper seat tightness below the set pressure.

What is valve calibration in pressure relief valve testing?

Valve calibration refers to verifying or adjusting the set pressure at which the valve opens.

Accurate Pressure Relief Valve Testing Requires the Right Setup

Field testing introduces variables that can impact accuracy and consistency.

That’s why accurate setpoint verification and defensible documentation are critical when testing both safety valves and relief valves.

Today’s facilities expect:

• Defensible, audit-ready documentation
• Digital reporting (not handwritten notes)
• Accurate setpoint verification
• Minimal downtime
• Repeatable, consistent data across technicians 

The challenge is achieving all of that in real field conditions.

The AccuTEST System is designed to remove the variability from in-line pressure relief valve testing by enabling:

• Real-time digital data capture for accurate, traceable results
• Automated test sequences that reduce technician variability
• Smooth, controlled force application with a motor (not a hand jack) for consistent loading
• Branded PDF reports for clear, professional documentation
• One-technician operation to improve efficiency in the field
• Remote U.S.-based support when it’s needed

If you’re evaluating how your team tests safety valves and relief valves, it may be time to move toward a more controlled, repeatable testing approach.

Request a live demo of the AccuTEST System and see how modern testing improves accuracy and efficiency.

• Category: Pressure Relief Valve, Safety Valve Testing