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Trapped Key Interlocks

Trapped Key Interlocks are mechanical locking devices used to control safety-critical operating procedures. The interlocks can be fitted to a wide range of control devices including power switches, access doors and hatches, as well as valves of all types. The transfer of keys from one interlock to another compels operators to follow predetermined sequences of operation. Here are a couple of examples:


Alcatraz valve wheel interlockCritical valve process systems, e.g. PSV safety relief valves or pig launcher receiver systems incorporate a series of valves which are used to maintain the safety integrity of the process. Inadvertent or unauthorized operation of these valves can lead to massive system failures, leakage of hazardous gases or fluids and ultimately, explosion. Fitting these valves with key interlocks ensures that valves can only be operated under controlled conditions, and in the pre-determined sequence which they were intended.

Total Lockout offer a broad range of Valve interlock solutions – Lever operated valves, Wheel operated valves, Motorized valves, Pig trap and Pig launch / receiver.




Alcatraz bolt interlockIt’s normal for potentially dangerous machinery to have perimeter guards placed around it to keep workers away from the dangerous moving parts. Inevitably, when maintenance is required, workers must pass through the guarded area to work on  the machine. A key interlock system can keep workers safe by locking the guards in place. The key to unlock and open these guards is retained in the machine power isolating switch. In this way, the only way to unlock and open the guards is to switch off the power. The locks on the guards retain the key when the guard is open. This prevents power being restored to the machine until the workers have retreated from the guarded area.

View our range of Machine guarding products – Switch interlocks, Access control, Key exchange box, Timer delay interlock, Shoot bolt, Solenoid control interlock.

Greatly reduce the risk of accidental or unauthorized operation of equipment using a trapped key interlock system. Interlocks a designed to be permanently fitted to their host equipment, whether that is valves, switches or machine guards.

In the case of safety critical process pipeline valve systems, a risk assessment will determine the likely consequences of inadvertent valve operation. The same rules of risk assessment apply to manufacturing operations where cleaning and maintenance workers need periodic access to potentially dangerous moving parts. Integrating a key interlock system with guarding systems on machinery can provide a high integrity safety control system which compels workers for follow pre-determined steps which isolate energy sources while maintenance work takes place.

In high pressure working environments, where commitment to production deadlines may exist workers can become distracted, increasing the potential to make mistakes at crucial times. When operating machinery or process plant, even a simple mistake can have serious consequences – and not just for the individual doing the work.

If the consequences could lead to a major incident resulting in significant loss, whether that be loss of product, damage to equipment or injury or death to personnel, a trapped key interlock system from Total Lockout is the only viable solutions.

Key Interlocks have been in existence for almost 100 years. They provide a purely mechanical method of implement safe working practices, and unlike electronic control systems, are sometimes considered infallible. Even when power systems fail, the trapped key interlock system maintains a last line of defence against potential injury.

Because key interlocks are such a niche product, the pool of knowledge and expertise is small. At Total Lockout we have over 50 years of industry experience. We believe that by freely sharing information and knowledge negative preconceptions about the capability of interlocks can be overcome. In short, if people have experience or a basic understanding of Interlocks, they are more likely to consider using them for their potentially hazardous application.

Total Lockout have a range of key operated mechanical Interlocks that compel any Operator to adhere to a strict, pre-determined sequence of operation.

Operating keys with unique codes are passed from Interlock to Interlock within the system, making it impossible to not complete the work safely. Even if the Operator is unfamiliar with the task to be undertaken or becomes distracted in some way, the key Interlocks ensure the job is always completed correctly and safely.


consulting-imageTotal Lockout aims to simplify the implementation of key interlock systems by providing clear and concise advice. This is a two-way street, in the first stage we listen to your inquiry to fully understand your requirements, objectives and needs. Only when we understand your specific requirements can we give good, qualified advice.

Total Lockout offers a range of standard key interlock products either for valves and process equipment, electrical switchgear or machine guarding applications. This includes, valves interlocks for safety relief (PSV) systems and pig launchers and receivers. For machine guarding applications we offer Isolating Switch Locks, Solenoid Control interlocks and Timer Delay Units, keys exchange boxes, access door and gate interlocks.

We can design interlock systems for robot cells, millers, grinders, crushers and balers. Also industrial oven interlock systems, conveyors, shears and other cutting systems.

Our expertise as experienced engineers allows us to offer design capability for the most complex procedures and host equipment. In doing so, we can design out complexity and design-in simplicity and integrity.

If this service sounds attractive, please contact us to discuss your requirements.

We will provide you with fast, accurate unbiased advice and opinions on your application(s) and we offer this service free of charge.

We look forward to hearing from you!

If you’d like a visit to discuss your requirements, call the office or our UK partner Derwent James Ltd.

Once implemented, key interlocks are a simple concept to understand and use. The requirement for training is limited to installation, commissioning and periodic maintenance.

If you require training for key interlock systems contact us today to discuss your requirements.

Americas: (727) 608-4325

UK and Rest of World: +44 (0)1376 325506


We offer an interlock consultation service to evaluate your potential needs for key interlocks, both machine guard applications, switchgear and valve interlock systems.

The consultation usually begins with a telephone conversation to establish if a key interlock system is the most suitable and appropriate solution.

We can visit your workplace to carry out a survey of equipment to be interlocked. In the case of valve interlock systems, we also offer to carry out detailed dimensional survey of all valves. From this information gathered, we can design and manufacture the mounting kits required to fit the interlocks to the valves.

At all times, we communicate our findings and recommendations in an easy to understand way, making it easy for you to decide on the way forward.