How to Select Pressure Relief Valves for Industrial Plants

If a pump fails, production stops. If a control valve fails, the process drifts. But if a pressure relief valve (PRV) fails, people can get hurt.

Selecting the right safety device is not just about matching a pipe size. It is an engineering discipline that sits at the intersection of fluid dynamics, thermodynamics, and mechanical integrity. A valve that is too small won’t relieve pressure fast enough to prevent an explosion. A valve that is too big will “chatter”, destroying its own seat and causing leaks within seconds.

We see many facilities struggle with this complex choice. In this guide, we break down the critical engineering factors you must evaluate when choosing Pressure Relief Valves for industrial plants.

1. Know Your Fluid State (Gas, Liquid, or Steam?)

The first question isn’t “what pressure?”—it is “what phase?”

A valve designed for incompressible liquid (like water) behaves very differently from one designed for compressible gas (like nitrogen or steam).

• For Gases/Steam: You typically need a valve that “pops” open instantly to release maximum volume.
• For Liquids: You often need a relief valve designed for “trim” opening to prevent water hammer (a sudden pressure shockwave) that can rupture pipes.

The Rule: Never swap a liquid-trim valve for a gas-service valve without consulting a specialist. The flow characteristics are fundamentally different.

2. The “Hidden” Factor: Back Pressure

This is the most common trap in PRV selection.

When a valve opens, it usually vents into a discharge header pipe that is collected with other valves. This pipe might already have pressure in it from other processes. This is called Back Pressure.

Ideally suited for when venting directly to the atmosphere. However, if there is variable back pressure in the discharge pipe, it pushes against the valve disc, changing the set pressure. This makes the valve unreliable.

• Balanced Bellows PRVs: These contain a metal bellow that shields the moving parts from back pressure. If your discharge header pressure fluctuates, you must select a balanced bellows design.
• Pilot-Operated PRVs: For extremely high back pressures or when you need to operate very close to the set pressure, a pilot valve uses the system pressure itself to keep the valve sealed tight until the exact moment it needs to open.

3. Temperature and Material Compatibility

Selecting Pressure Relief Valves for industrial plants requires a deep look at the material compatibility table.

Standard Carbon Steel bodies (WCB) are fine for general utilities. However, if you are handling corrosive acids, sour gas (H₂S), or cryogenic fluids (LNG), standard materials will fail.

• High Temperature: Chrome-moly steels may be required to prevent metal creep.
• Low Temperature: Stainless steel (316) is often needed to prevent brittle fracture in cold climates or cryogenic services.

Tip: Always specify if your valve needs NACE compliance (for sour gas environments) to prevent sudden cracking of the valve body.

4. Sizing: The “Goldilocks” Principle

Sizing is where the math happens (specifically, API 520 calculations).

• Undersized: The valve opens, but pressure continues to rise because the valve can’t vent fluid fast enough. Result: Vessel failure.
• Oversized: The valve opens, vents too fast, pressure drops instantly, the valve slams shut, pressure rises again, and the valve pops open again. This rapid “chatter” destroys the valve internals and flange faces.

You need a valve that is sized exactly for your required relieving capacity—no more, no less.

5. Connection Types and Standards

Are you following API 526? This standard dictates the flange dimensions and center-to-face measurements.

• Why it matters: If you select an API 526 compliant valve, you know that years from now, you can swap it out with another brand’s API 526 valve and it will fit perfectly into the same pipe gap. It future-proofs your facility.

Conclusion: Trust the Specialists

There is no “off-the-shelf” solution for safety. Every PRV must be sized and selected for the specific tag number it serves.

ADYAA sells valves and calculates them. Our engineering team reviews your process conditions against the latest standards to ensure your Pressure Relief Valves for industrial plants will perform when the alarm bells start ringing.

Unsure if your current valves are sized correctly?  

Contact ADYAA for a Pressure Relief Audit. Speak to our technical team about API 520 sizing today.