Understanding what a relief valve is starts with its core purpose: protecting pressurized systems from dangerous overpressure conditions. When system pressure rises above a preset limit, the valve opens to safely divert gas, lowering pressure and preventing equipment damage, or failure. In simple terms, what is a relief valve? It’s an automatic safety release that keeps your system within safe operating limits.

In this guide, we explain how relief valves work, common types, where they’re used, and the benefits they deliver. We also clarify related terms customers often ask about, so you can make confident, informed decisions.

How Relief Valves Work

A relief valve is set to open at a specific pressure, called the set point. As system pressure approaches that set point, the internal mechanism begins to lift and allows flow out of the valve. Once pressure falls below the reseat value (often known as blowdown), the valve closes and normal operation resumes. Put simply, what does a pressure relief valve do? It senses when pressure gets too high and automatically vents enough to bring it back down safely.

Key components include:
• Spring or pilot mechanism that determines the set pressure
• Valve body, seat, and sealing surfaces that prevent leakage when closed
• Disc or poppet that lifts to permit flow during overpressure
• Inlet and outlet connections sized for the required relief capacity
• Adjustment mechanism for precise calibration and testing

Many designs use soft seats for tight sealing and o-rings to fine-tune opening and reseating behavior.

PRVs: Relief Valves vs. Pressure Reducing Valves

If you’re wondering “what is PRV?”, it’s commonly used to refer to both pressure relief valves and pressure reducing valves, so context matters. A relief valve protects against high pressure; a reducing valve controls and lowers downstream pressure during normal operation.

Customers often ask what is a pressure reducing valve and how it differs from a relief valve. A pressure reducing valve is designed to lower and maintain downstream pressure at a set level during normal operation. It throttles flow to keep system pressure below the setpoint, even as inlet pressure fluctuates. By contrast, a relief valve sits as a safety device and remains closed under normal conditions; it opens only when pressure exceeds the safe limit.

To avoid confusion: if the goal is safety and overpressure protection, you need a relief valve. If the goal is controlled system pressure, you need a pressure reducing valve. Understanding what is a relief valve and what is a pressure reducing valve ensures you pick the right solution for your application.

Types of Relief Valves

Relief valves are engineered for different media, pressures, and system behaviors. Common types include:

• Spring-loaded relief valves: A calibrated spring keeps the disc closed until system pressure exceeds the set point. Simple, robust, and widely used for steam, gas, and liquids.
• Pilot-operated relief valves: A small pilot controls a larger main valve, delivering precise set pressure, minimal leakage, and stable operation across broad flow ranges. Ideal for high-pressure and hydraulic services.
• Differential pressure relief valves: Open based on pressure difference between two points, protecting filters, heat exchangers, and vessels from excessive differential pressure.

If you’re evaluating what is a relief valve that’s best for your system, consider whether spring-loaded simplicity or pilot control precision is better suited to your conditions.

Check out our complete offering of relief valves here.

Where Relief Valves Are Used

Relief valves safeguard equipment and personnel across many sectors:

• Industrial process systems: Reactors, storage tanks, pump discharge lines, and compressors rely on relief valves to manage upset conditions and transient spikes. Water and wastewater facilities use them to protect pumps and piping from surge events. Fire protection networks apply relief valves to prevent overpressure.
• HVAC and building systems: Chillers, boilers, and hydronic loops use relief valves to maintain safe pressures and guard against thermal expansion. Refrigeration circuits depend on them to prevent excessive pressure from temperature changes or compressor faults.
• Oil and gas: Wellheads, separators, pipelines, and gas processing equipment incorporate relief valves to meet safety standards and act as a last line of defense against overpressure incidents.

Benefits of Using Relief Valves

Relief valves deliver measurable safety and performance advantages. In practical terms, what does a pressure relief valve do for your operation? It reduces risk, protects assets, and stabilizes processes.

• Enhanced safety: Automatic overpressure protection helps prevent incidents by venting excess pressure before failures occur.
• Equipment protection: Limiting peak pressures extends the life of pumps, compressors, heat exchangers, and piping while reducing downtime and repair costs.
• Regulatory compliance: Relief valves support adherence to codes and standards such as ASME Boiler and Pressure Vessel Code, relevant API standards, and local mechanical codes. Proper selection, sizing, installation, and testing are essential for certification and insurance.
• Operational stability: Relief valves smooth out pressure excursions during transient conditions and help prevent nuisance trips and maintenance issues.

Frequently Asked Questions

How do you set the pressure on a relief valve?

Most spring-loaded valves use an adjustment screw to compress the spring. Technicians set the valve with calibrated gauges and follow manufacturer procedures. Pilot-operated designs are set by adjusting the pilot’s set point. Always verify set pressure with a test bench or in-situ testing per applicable code.

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

Safety valves typically refer to rapid-opening valves for compressible fluids like steam and gas, often with a “popping” action. Relief valves may open more gradually and are widely used for liquids. Many standards use the terms interchangeably; selection should match the fluid, service, and code requirements. Safety Relief Valves need to be certified by ASME or the National Board. Standard relief valves do not.

What information is needed to size a relief valve?

Key data include set pressure, allowable overpressure or build-up pressure, media type and properties, required relief rate (mass or volumetric flow), inlet temperature, backpressure, and connection sizes. For code compliance, include design pressure and applicable standards (such as ASME and API). Accurate sizing ensures proper capacity and reliable reseating.

Quick Reference: Relief Valve vs. Reducing Valve

Selecting the Right Valve for Your Application

With decades of experience, we help customers match the right technology to the application. Whether you need robust spring-loaded protection, precise pilot-operated control, or guidance on sizing and compliance, our team can support you from selection through commissioning.