Valves

Fail Open Vs Fail Close valves

What is fail open and fail close valve?

Terms like “Fail-Open” and “Fail-Close” are used to describe how valves behave under specific conditions, especially when there is a loss of power or control. In industrial processes, automation, and safety systems, these phrases are frequently used.

What is FO and FC valve?

Definitions

Fail Open (FO)

Fail Open Vs Fail Close valves1

A fail-open valve is a kind of valve that opens automatically and stays open when it loses power or control. To put it another way, the valve will turn to the open position in the event of a control system malfunction or a power outage, allowing fluid or gas to pass through the pipeline.

When a signal or power is lost, a valve would open and be said to fail open. To remain closed, these valves need air pressure. The valve will automatically open after the required air pressure has been removed. The air pressure source would be lost after a power outage, causing the valve to “fail” open.

Fail Closed (FC)

Fail Open Vs Fail Close valves 2

Fail closed means the valve will close if the signal is lost or stopped. Compared to the earlier example, this is the opposite. The valve automatically closes when power is removed since there is no longer a functioning air source, and air pressure is required to keep the valve open.

When it loses control or power, a fail-close valve is a type of valve that automatically closes (remains in the closed state). The valve will turn to the closed position in the event of a malfunction or power outage, preventing any fluid or gas flow in the pipeline.

What is the difference between fail close and fail open valves?

Differences

The main difference between fail-open and fail-close valves lies in their response to failures:

Fail-Open Valve: The valve opens in case of failure, allowing the flow to continue.

Fail-Close Valve: The valve closes in case of failure, stopping the flow.

Requirements

The decision between a fail-close valve and a fail-open valve is based on the application, safety factors, and process requirements. Among the things to take into account are:

Safety

A fail-safe system is necessary in some critical applications to avoid catastrophes or equipment damage. For safety, picking the right fail-open or fail-close valve can be essential.

Process control

It is necessary to assess the process needs and the effects of a flow disruption. For instance, fail-close valves may be required in emergency shutdown systems to rapidly stop the flow of dangerous materials.

Reliability

It is crucial that the valve function reliably under various circumstances, including failure scenarios. When required, the valve should function as planned.

What is the difference between fail open and fail close application?

Applications

Fail-Open Valve Applications

In applications where it is safer for the flow to continue even in the case of a failure, fail-open valves are frequently employed. Examples include transporting non-hazardous fluids, cooling systems, and water supply lines.

Fail-Close Valve Applications 

In order to stop the discharge of dangerous materials, fail-close valves are frequently utilized in crucial processes and safety systems. Examples include safety relief valves, gas pipelines carrying flammable materials, and emergency shutdown systems.

Designing Fail-Open and Fail-Close Valves

In order to accomplish the intended functions of fail-open and fail-close valves, the design of these valves must require the use of distinct mechanisms.

Fail-Open Valve Design

Fail Open Vs Fail Close valves 3
  • When power or control is present, fail-open valves often use springs or other mechanical devices to hold the valve in the closed position. When a mechanism malfunctions, it releases, allowing the valve to open against the force of the fluid or gas flow.
  • Fail-open valves are built with a closed position as the default. While there is power or a control signal, the actuator or control system keeps the valve in the closed position. When there is a malfunction, the actuator releases the valve, which is then moved to the open position by a spring or other mechanical device.
  • In systems where it is safer to permit fluid or gas flow to continue in the case of a control system failure, fail-open valves are frequently employed. For instance, in cooling systems, it might be advantageous for the fluid to keep flowing even in the event of a power failure to prevent overheating.

Fail-Close Valve Design

Fail Open Vs Fail Close valves4
  • On the other hand, fail-close valves are intended to have a default open position. While there is power or a control signal, the actuator or control system keeps the valve in the open position. When a malfunction happens, the actuator releases the valve, which is then moved to the closed position by a spring or other mechanical device.
  • In situations where it is essential to halt the flow of fluid or gas right away in the event of a breakdown, fail-close valves are frequently employed. Fail-close valves, for instance, ensure that no hazardous compounds are released into the environment, protecting people and equipment in emergency shutdown systems or safety relief valves.

When selecting valves what factors are to be considered?

Factors Affecting Valve Selection

The selection of fail-open or fail-close valves for certain applications is influenced by a number of considerations.

Process safety

 A fail-close valve may be selected to prevent accidents and protect people and property in processes involving hazardous materials or critical circumstances.

System Requirements

The type of valve that should be used depends on the system’s unique requirements, such as flow control, pressure regulation, or cutoff capabilities.

Redundancy 

For increased security and dependability, redundant fail-open and fail-close valves may occasionally be employed.

Power supply

Especially in remote or crucial installations, the availability and dependability of the power source will affect the decision between a fail-open or fail-close valve.

Process Conditions

The material choice and design of the valve will be influenced by the characteristics of the fluid or gas being regulated, including pressure, temperature, and corrosiveness.

Fail-open and fail-close valves are crucial parts of automated systems, safety applications, and industrial processes. Their actions during malfunctions or power outages determine the system’s overall safety and dependability. To maintain optimal performance and protect people and equipment in a variety of applications, careful evaluation of process requirements, safety issues, and suitable valve design is required. Understanding the distinctions and making educated judgments are essential for successful and safe operation, whether choosing a fail-open or fail-close valve.

What is fail locked in last position?

Lock in last position (FL)

A “lock in last position” valve, also known as a “fail-last valve,” keeps its present state—whether it is open or closed—during a power outage or a system malfunction. It ensures stability, safety, and process control in safety-critical applications like fire suppression or emergency shutdown systems. Without requiring any outside power, the valve stays in place by mechanisms like mechanical locks or springs. By preventing rapid changes in flow, pressure, or material release, this feature improves operational safety and reliability across a range of sectors.

What is the difference between fail open and fail close valve symbol?

Fail Open Vs Fail Close valves 5
Fail Open Vs Fail Close valves 6

Fail-Open Vs Fail-Close Valves

AspectFail Open ValveFail Close Valve
FunctionAutomatically opens on power loss or system failureAutomatically closes on power loss or system failure
SafetyGenerally used in systems where a loss of fluid or pressure is saferGenerally used in systems where preventing fluid loss or pressure is safer
ApplicationsSteam systems, emergency relief, cooling water systemsProcess control, pipelines, oil and gas systems
Control LogicRequires external control (e.g., electric actuator) to closeRequires external control (e.g., electric actuator) to open
Pressure LossMay lead to pressure loss if the valve is open when a failure occursPrevents pressure loss if the valve is closed when a failure occurs
Fail PositionOpen by default, closed when activatedClosed by default, open when activated
Response TimeGenerally faster response time to fail openGenerally faster response time to fail close
MaintenanceEasier to inspect and maintain in fail-open positionEasier to inspect and maintain in fail-close position
ExampleEmergency relief valve in a steam systemValve in an oil pipeline to prevent leaks

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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