How to choose the right relief valve for your industrial system

Selecting the right pressure relief valve is a critical factor in any industrial installation that handles fluids under pressure.

These valves protect equipment, people, and processes against unwanted pressure increases, ensuring the stability and proper operation of the system.

In this article, we will take a detailed look at how these valves work, what factors you should consider when choosing the most suitable model, and what solutions Valfonta offers for different industrial sectors.

What is a pressure relief valve?

A pressure relief valve is a device designed to open automatically when the pressure in a system exceeds a preset pressure, allowing the controlled release of fluid and preventing structural damage or accidents.

Its main function is to protect the system against overpressure that could compromise the integrity of pipes, vessels, pumps, or other critical components. Although they are often confused, relief valves and safety valves serve different functions.

While safety valves are designed to open immediately in extreme emergency situations, relief valves respond progressively to small pressure increases, providing more precise control and preventing sudden fluctuations in the system.

These valves are essential in industries such as chemicals, food, energy, and pharmaceuticals, where pressure control is vital for production processes to run correctly.

How does a pressure relief valve work?

The operating principle of a pressure relief valve is simple yet highly effective. Normally, the valve remains closed as long as the system pressure stays below the defined set point. When the inlet pressure exceeds this limit, the force of the fluid overcomes the resistance of the internal spring or actuator, causing the plug to open progressively​​.

This movement allows part of the fluid to escape, thereby reducing the pressure in the line until normal conditions are restored. Once equilibrium is restored, the spring returns the plug to its original position and the valve closes automatically.

In Valfonta models, such as the S1 or S2 excess pressure valves and the S3 relief valves, this operation is achieved through highly sensitive self-operated systems capable of working with steam, compressed air, inert gases, or liquids, ensuring effective control over a wide range of pressures and temperatures.

Key factors in choosing a relief valve

Fluid type

The first fundamental criterion is the type of fluid that will flow through the valve. Not all models are suitable for every medium.
Valfonta relief valves are designed to work with:

• Steam
• Compressed air
• Inert gases
• Industrial liquids​​​.

For example, for high-temperature steam, you will need a model that can withstand those extreme thermal conditions, such as the S3​.

For corrosive fluids, it may be advisable to choose valves made of AISI 316L stainless steel​​.

Working pressure range

Each valve has a specific pressure range within which it can operate safely and effectively. It is essential to know both the normal working pressure and the pressure peaks that may occur.

Examples of regulation ranges in Valfonta products:

• Model S1: from 0.1 to 15 barg​.
• Model S2: from 0.02 to 10 barg​.
  Model PRV53: from 0.5 to 10 barg​.
• Model PRV55: from 0.01 to 8 barg​.

Selecting a model that operates within the right range extends the service life of the valve and improves the safety of the entire system.

Operating temperature

Fluid temperature is another critical parameter.
Each diaphragm and gasket material has a safe operating temperature limit:

• NBR: -20ºC to 80ºC
• EPDM: -40ºC to 125ºC
• PTFE: up to 220ºC​​.

In steam or very hot fluid applications, you must make sure that both the body and the internal components of the valve can withstand the expected temperature.

Construction materials

The materials of the body and internal components will determine the valve’s resistance to corrosion, pressure, and temperature.

At Valfonta we use materials such as:

• RG10 bronze
  A216 WCB carbon steel
• A351 CF3M stainless steel​​​.
• Duplex or super duplex (on request)

For demanding environments or aggressive fluids, we recommend choosing versions made entirely of stainless steel.

Connections and regulations

Another aspect to consider is the valve’s connections:

• DIN PN16–PN40 flanges
• ANSI 150/300 flanges
• BSP or NPT threads​​.

It is also essential that the valves comply with current European regulations such as the Pressure Equipment Directive PED 2014/68/EU and, where applicable, ATEX certification for explosive atmospheres.

Types of Valfonta pressure relief valves

At Valfonta we offer a complete range of pressure relief valves to meet the needs of different industrial sectors. Each model is designed for specific fluid types, pressure ranges, and temperatures. Below is a summary of our most popular models:

In addition, all our models can be supplied with different sealing options (NBR, EPDM, PTFE, FKM) and connections to the most demanding industrial standards (DIN, ANSI, BSP, NPT).

Each product datasheet is available on our website so you can review all the detailed specifications, or you can contact our technical department directly for advice on the most suitable choice.

Pressure relief (or pressure-relieving) devices: which model to choose

Valfonta pressure relief devices (PRV54, PRV55, S1, S2, and S3) maintain upstream pressure and discharge the excess proportionally. To choose between them, first look at three data points:

• Set pressure. From 0.01 barg with the PRV55 and from 0.02 barg with the S2, up to 20 barg with the S3.
• Size. The PRV54 and PRV55 range from DN15 to DN25; the S2 goes up to DN100, and the S1 and S3 up to DN150 (on the S3, DN125 and DN150 on request).
• Fluid and temperature. With steam, the S1 and S3 work up to 220 °C and the PRV54 up to 210 °C.

If what you need is to protect equipment against overpressure, you need a safety valve, not a relief valve. You will find the full comparison of the range on our relief and excess pressure valves page.

Installation and maintenance tips

Prior cleaning of the circuit

Before installing the valve, it is essential to thoroughly clean the inside of the pipes to remove solid particles or impurities that could damage the internal components​​.

Strainer installation

 We recommend installing a strainer upstream of the valve to protect the seat and plug from solids carried by the fluid.

Horizontal mounting

Valfonta pressure relief valves must be installed in horizontal pipes, following the flow direction indicated by the arrow on the body​​.

Avoid mechanical stress

Pipe supports should be located as close as possible to the flanges, so that no weight or stress is placed on the valve or the actuator.

Proper control connection

On models that require an external pressure sensing point (such as the S1), it must be installed at least 1 meter from the valve, using suitable tubing​.

Overheating protection

In steam or hot liquid systems, it may be necessary to install a condensate water seal pot to protect the diaphragm​.

Periodic inspection

Although Valfonta relief valves require little maintenance, regular inspections are recommended to check for leaks, plug wear, or diaphragm deformation.

Set point calibration

If deviations in the opening pressure are detected, it is important to recalibrate the valve following the manufacturer’s instructions, adjusting the adjusting nut or screw​​.

Preventive component replacement

Under extreme conditions or intensive use, it may be advisable to replace gaskets and diaphragms after a certain number of opening/closing cycles, always using genuine spare parts kits.

Proper storage

If the valve is not installed immediately, store it in a dry place, protected from moisture, dirt, and extreme temperatures.

Relief valve start-up

To start operating a relief valve, careful steps must be followed to avoid problems such as water hammer, which can damage the system and the valve. Below are the basic start-up steps:

Benefits of properly adjusting the relief valve

These benefits make adjusting a relief valve an essential practice in any system that requires precise pressure control.

If you already know what your installation needs, see our range of pressure relief valves or the datasheet for the S3 pressure relief valve.