LESER Safety valves for all industrial applications

Safety valves for all industrial applications

LESER Safety valves for all industrial applications

LESER-API-Safety valve


Pressure valves according to API 526 with standardized capacities and dimensions

LESER-Pilotventil-Pilot valve-Safety valve

High Efficiency

Solutions for high plant efficiency

LESER-Thermal relief valve-Thermisches Sicherheitsventil-Safety valve

Compact Performance

Safety valves with compact dimensions and high connection variety

LESER-High Performance-Safety valve

High Performance

Safety valves for all industrial applications

LESER-Proportioning valve-Modulating valve-Safety valve

Modulate Action

Safety valves for low pressure dynamics


Best Availability

Additional products for higher plant availability

LESER-Clean Service-Type 483-Safety valve-Sicherheitsventil_01

Clean Service

Safety valves for food, beverage and pharmaceutical applications

LESER-Critical Service-PTFE valve-Safety valve-Sicherheitsventil

Critical Service

Safety valves with PTFE-lining for corrosive media

LESER-Heater valve-Heizungsventil-Safety-valve-Sicherheitsventil


Safety valves for heating systems


Basic Knowledge of Safety Valves

What is a Safety Valve?

The primary purpose of a safety valve is the protection of life, property, and the environment. A safety valve is designed to open and relieve excess pressure from vessels or equipment and to reclose and prevent the further release of fluid after normal conditions have been restored.

Safety Notice

A safety valve is a safety device and in many cases the last line of defence. It is important to ensure that the safety valve is capable of operating at all times and under all circumstances. A safety valve is no process valve or pressure regulator and should not be misused as such. It should have to operate for one purpose only: overpressure protection.

There is several reasons why the pressure in a vessel or system can exceed a predetermined limit. API Standard 521/ISO 23251 Sect. 4 provides a detailed guideline about the causes of overpressure. The most common are:

  • Blocked discharge
  • Exposure to external fire, often referred to as a “Fire Case”
  • Thermal expansion
  • Chemical reaction
  • Heat exchanger tube rupture
  • Cooling system failure

Each of the above-listed events may occur individually and separately from the other. They may also take place simultaneously. Each cause of overpressure also will create a different mass or volume flow to be discharged, e.g. small mass flow for thermal expansion and large mass flow in case of a chemical reaction. It is the user’s responsibility to determine a worst-case scenario for the sizing and selection of a suitable pressure relief device.

Types of Safety Valves

In the context of pressure relief devices, a fundamental distinction can be made between reclosing and non-reclosing devices. Safety valves are part of the reclosing devices and are differentiated based on their loading principle or controllability. 

In addition, a distinction can be made based on the function of the valves. Here, a distinction is made between relief valves (full lift)normal safety valves, and proportional safety relief valves.

There are two main types of safety valves: Spring-loaded safety valves and pilot-operated safety valves. Also relevant are so-called change-over valves, which ensure continuous system availability (not included in the illustration)

How does a Safety Valve work?

The function and design of safety valves differ depending on the main type or loading principle. Use the following buttons to navigate to the respective main type pages. There you will find the corresponding LESER safety valves as well as further information, for example on the function and design of the main types.

Sizing of Safety Valves

To ensure the greatest possible plant safety, the analysis of the conditions and requirements of an application and the corresponding dimensioning of a safety valve is crucial. Determining the necessary dimensions and flow cross-section of a safety valve is referred to as “sizing the safety valve”Numerous parameters are taken into account in this calculation.

Examples of relevant substance data:

  • Type and aggregate state of the medium
  • Design standard (DIN, API, AD, ASME)

Examples of relevant operating data:

  • Set pressure
  • The operating temperature of the medium
  • Required mass flow (e.g. 10,000 kg/hour)

Safety Valve Symbols

The main types of safety valves are identified by symbols. Therefore, there is not only one but several safety valve and safety valve symbols. They are often shown on safety valves or their packaging. In addition, they are used in technical drawings and schematics as well as system sketches – for example, in the description of DIN standards.

The following symbols are related with the main types of safety valves:

safety-valve-symbol             Spring-loaded Safety Valves and Pilot-operated Safety Valves

change-over-valve-symbol     Change-over Valves


What is a safety valve used for?

The primary purpose of a safety valve is to protect life, property, and the environment. Safety valves are designed to open and release excess pressure from vessels or equipment and then close again.

How does a safety valve work?

The function of safety valves differs depending on the load or main type of the valve. The main types of safety valves are spring-loaded, weight-loaded, and controlled safety valves.

What is the set pressure of a safety valve?

Regardless of the type or load, safety valves are set to a specific pressure at which the medium is discharged in a controlled manner, thus preventing overpressure of the equipment. In dependence on several parameters such as the contained medium, the set pressure is individual for each safety application.