Safety Valve vs Relief Valve: What Is the Difference?

Safety valves and relief valves are both used to protect industrial equipment and piping systems from excessive pressure. Although they have similar pressure protection functions, they are not always used in the same applications.

Understanding the difference between a safety valve and a relief valve is important when selecting pressure protection equipment for boilers, pressure vessels, pipelines and industrial process systems.

This guide explains the key differences between safety valves, relief valves and safety relief valves, as well as the main factors to consider when selecting one.

1. What Is a Safety Valve?

A safety valve is a pressure protection device designed to automatically release pressure when the system reaches a predetermined set pressure.

Safety valves are commonly associated with applications involving compressible fluids, such as steam and gases.

When the pressure reaches the set point, the valve opens to discharge the excess pressure. Once the pressure falls to a safe level, the valve can close again.

Typical applications include:

• Steam boilers
• Power plants
• Pressure vessels
• Steam systems
• Gas systems
• Petrochemical processes

Safety valves are especially important in systems where uncontrolled pressure increases could create serious equipment or process hazards.

2. What Is a Relief Valve?

A relief valve, also known as a pressure relief valve in many applications, is designed to protect a system from excessive pressure by relieving excess fluid.

Relief valves are commonly used with liquids, where the pressure response and valve opening characteristics differ from typical steam or gas applications.

Typical applications include:

• Pumps
• Liquid pipelines
• Chemical processing
• Hydraulic systems
• Water systems
• Industrial process equipment

The valve opens when the system pressure reaches the specified set pressure and discharges fluid to reduce the pressure.

3. Safety Valve vs Relief Valve

The main difference is related to the type of fluid and opening characteristics.

However, terminology can vary between industries, standards and manufacturers. Some products are designed as safety relief valves and can be used for both liquid and compressible-fluid applications.

Therefore, the actual valve specification and applicable standards should always be checked rather than selecting a valve based only on its name.

4. What Is a Safety Relief Valve?

A safety relief valve combines characteristics of both safety and relief valves.

Depending on the design and application, it can be used for pressure protection in systems containing liquids, gases or steam.

Safety relief valves are commonly used in industries where the process conditions can vary or where a flexible pressure protection solution is required.

For example, industrial plants may use safety relief valves in:

• Chemical processing
• Oil and gas
• Petrochemical plants
• Power generation
• Pressure vessels
• Process piping

The appropriate valve design should be selected according to the medium, pressure, temperature, required capacity and applicable standards.

5. How Does a Safety or Relief Valve Work?

The basic operating principle is relatively simple.

Under normal operating conditions, the valve remains closed and allows the process system to operate at its normal pressure.

When system pressure reaches the specified set pressure, the valve begins to open and releases part of the process medium.

This reduces the system pressure and helps prevent excessive pressure from damaging equipment.

Important parameters typically include:

• Set pressure
• Operating pressure
• Relieving pressure
• Blowdown
• Flow capacity
• Temperature
• Connection size
• Pressure rating
• Material compatibility

Correct sizing and setting are essential for effective pressure protection.

6. How to Choose the Right Valve?

When selecting a safety valve or relief valve, start with the actual process conditions.

Consider:

Medium

Is the system handling:

• Steam?
• Gas?
• Air?
• Water?
• Oil?
• Chemical liquid?

Pressure

Check:

• Normal operating pressure
• Set pressure
• Maximum allowable working pressure
• Required relieving pressure

Temperature

The operating and relieving temperatures can affect material selection, sealing and valve performance.

Flow Capacity

The valve must be capable of relieving enough fluid to protect the equipment under the defined overpressure scenario.

Materials

Wetted materials should be compatible with the process medium and operating conditions.

7. Common Industrial Applications

Safety and relief valves are used across many industries.

Oil & Gas
Used for pressure protection in pipelines, processing equipment and pressure vessels.

Chemical & Petrochemical
Protect process equipment from excessive pressure caused by process disturbances or thermal expansion.

Power Generation
Safety valves are widely used in steam and boiler systems.

Steel Manufacturing
Used in high-pressure process and utility systems.

Water Treatment
Relief valves can be used to protect pumps, pipelines and liquid systems.

For demanding applications, products from established manufacturers such as Crosby and Consolidated are commonly considered for industrial pressure protection applications.

8. Safety Valve Selection Checklist

Before requesting a quotation, prepare the following information:

• Process medium
• Normal operating pressure
• Set pressure
• Maximum allowable pressure
• Operating temperature
• Required flow capacity
• Valve inlet and outlet size
• Connection type
• Valve material
• Applicable standards

Providing complete process information allows the supplier to determine the appropriate valve type and configuration.

Safety Valve or Relief Valve: Which One Do You Need?

The choice between a safety valve and relief valve depends primarily on the process medium, pressure conditions, required relieving capacity and application.

As a general guideline:

Steam / Gas → Safety Valve

Liquid → Relief Valve

Mixed or specific pressure protection requirements → Safety Relief Valve

However, this is only a starting point. Actual selection should be based on the equipment requirements, applicable standards and manufacturer specifications.

If you need help selecting a safety valve or relief valve, provide the medium, pressure, temperature, flow requirement and connection size. Our team can help check the suitable configuration and provide a quotation.