Smith Flow Control and Netherlocks have merged. We are now Sofis.

Smith valve interlocks

Smith interlocks effectively improve employee safety, protect your plant and equipment and reduce the risk of damage to the environment.

Ensure a safe sequence of your valve operations.

Improving process safety

Historically you use a Permit to Work (PtW) and documented instructions to control the sequence of process activities. However, this system is hostage to ‘human factor’ distractions. Operators can fail to interpret instructions correctly or ignore the system, which could lead to industrial accidents. Smith interlocks are simple, mechanical devices, which you can customise to implement a safe sequence of operation in any process activity.

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Valve interlocks on gearbox valves
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Mechanical valve interlock types

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Key interlocks for safe pigging operations


In many process industries, incorrectly performed operations can have catastrophic consequences. Energy, process and tank storage industries generally have a disciplined approach to design and operating practice, usually governed by well recognised international standards. While good practice begins with good design, many procedures involve human intervention and may fall subject to operator error. Distributed Control Systems, (DCS) cannot effectively regulate such procedures. Smith valve interlocks can!

How can we help you?

With 30+ years of experience we can help you setting up safe valve operation sequences. Let us share the lessons we’ve learned with you by participating in HAZOP studies, sharing application knowledge and customized valve interlock solutions.

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Control system for safe valve operations

Safeguarding complex valve operations

To secure safe valve operating procedures, you might need to incorporate sensor signals into an interlocking sequence. If you need to ensure higher levels of process safety, we have various sequence control products available. They incorporate sensor information with traditional mechanical interlocking so you can reduce accidents and downtime.

Key management

With our new generation of intelligent interlock key management systems, you have various possibilities at your fingertips to optimise interlock and process performance. You can now utilise a vast array of additional data and intelligence, whilst ensuring safety of your operators and plant are held paramount.

Key management system for valve interlocks

Reference companies

Renowned companies use Smith interlocks as an industry standard to create a safer working environment.

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