Given that the car seal which is used for locking and sealing valves was originally designed for an entirely different application, some critical thought is needed to determine a specification that ensures that the device is fit for purpose.
The original car seal was designed to lock and seal railway cars that were transporting high value, tax generating goods, such as alcohol and tobacco across the railway network of the United States. The seal would deter opportunist theft and give evidence of tampering. The car seal is still widely used today for the same function and can be seen on the doors of shipping containers as they make their journeys aboard container ships and articulated lorries and semi-trailers.
In that application, the seal is a security measure, as opposed to a safety device.
The author has written many times about the subtle difference between safety and security, made more difficult when you consider that the French word sécurité means safety.
A device designed for the purposes of security needs to be sufficiently robust to not yield under attack from thieves. Whereas a safety device can be observed for its functional design to protect and thereby respected and not abused.
The car seal that has evolved for locking/sealing valves is very much a safety device. And because of this, the functional requirements which determine the materials of construction can be very different.
The valve car seal (safety device) needs to have a cable of sufficient length to wrap around the largest manual valve wheels. A meter length (39”) is generally regarded to be suitable. For small valves, excess cable can be cut off after fitting. The cable diameter can vary from 1.6mm to 5mm and car seals of these diameters are widely available today. That said, give some thought to the actual functional requirements of the cable diameter. The cable doesn’t need to provide a breaking strain measured in tonnes. It only needs to have adequate strength to not break during accidental or inadvertent attempts to turn a valve by hand and be cut without too much effort when the time comes to operate the valve. To that end, 2.5mm diameter is perfectly fit for purpose.
The size of the seal head needs to be big enough to display an 8 digit unique serial number and sometimes some bespoke client marking.
As for materials, valve car seals are often used in marine environments and therefore susceptible to accelerated corrosion. A stainless-steel multi-strand, 2.5mm diameter cable is best.
The head of the seal is traditionally made from zinc or aluminium and this is due to the method of construction being metal extrusion.
Where seals are to be used in Ex rated hazardous areas, users would be wise to choose a seal where the task of applying the seal to the valve will not generate a spark.
In conclusion, a valve car seal with 1000mm x 2.5mm cable and an aluminium head, color coded to indicate the status of the valve (red for closed, green for open) is everything you need for a successful car seal program.