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

Guiding You Through The Basic Principles Of Interlocking

Using NL Interlocks, you enforce and guarantee a predetermined valve operating sequence and eliminate human error.

Your Operators Are Guided Step By Step

Minimise Your Risk Of Human Error

When you choose Netherlocks Valve Interlocks, you eliminate human error. Using interlocks, you only allow the correct valve to be opened or closed in the correct sequence. You guide your operators every step of the way – there is no bypassing the system. Your valves are operated using a linear key, taking your operators through a specific process, following a predefined sequence, with unique keys for each step. Netherlocks Valve Interlocks are used as an industry standard by renowned companies like Total, BP, ADCO and Shell to create a safer working environment.

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Netherlocks Valve interlock on multi rotation valve

Discover the basics of valve interlocks

You should use Netherlocks Valve Interlocks where safe and ‘right-first-time’ valve operation is required. Your applications may include pressure relief valves (PSV), pig launching and receiving, inert gas systems, pump start up, flare lines, boiler blow-down, ‘2 out of 3‘ and decoking.

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A Product For All Your Process Requirements

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valve interlocks securing pressure relief valves


75% of the accidents in the process industry happen during startups, shutdowns and maintenance. In 50% of these accidents, root cause is incorrect operation of manual isolation valves. There are many applications where Netherlocks interlocks are an added value by protecting people, the environment or company assets.

Netherlocks Safety Systems and Smith Flow Control have merged. We are now Sofis.
Valve interlock key unit for controlling complex valve operations

Safeguarding complex valve operations

Valve interlocks are frequently used to secure linear valve operating sequences (open valve A, B and C and close in reversed order: C, B, A). Sometimes you must deviate from this linear procedure and repeat steps or return to previous steps, not in reversed order. Sequence control products guarantee these non-linear steps in a valve operating sequence.

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.

Valve interlock start key release is based on key detection and compressor inputs

Reference companies

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

BASF logo small
BP logo small
Sabic logo small
Shell logo small
Saudi Aramco logo small
Petronas logo small
Fluor logo greyscale
Chevron logo small

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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