From time to time valves need to be locked. The reasons can be varied. It might be necessary to isolate and vent pressure before maintenance engineers enter a vessel for cleaning. In another example, some valves need to be indefinitely locked off in order to provide continuity of process operations. Or perhaps operation of a number of valves must be carried out in a specific, predetermined sequence. Whatever the reasons, choosing the right valve lock that is appropriate for the application is not a complex task, but one that often holds uncertainty for those not experienced in this product selection.
Some valves are supplied with a built in padlock facility which makes the task of locking it quite straight forward. However, sometimes a padlock is not sufficient protection for the application.
Valves come in a wide range of shapes and sizes. Choosing the right locking device can seem a challenging task. But it doesn't have to be. It’s possible to filter out the right product by answering a few basic questions. No special knowledge about the specification or performance of the valve is needed.
Whether you have ball valves, gate valves, plug valves, globe valves or butterfly valves, there are two factors which determine what type of locking device is needed. These are the method of operation followed by the size of the valve.
Many valves are manually operated via a hand wheel, lever (wrench) or sometimes the valve might be power actuated e.g. electric motor, hydraulic or pneumatic actuator. Regardless of the method of operation, all valves can be locked out in some way.
Manual valves
For manual, wheel operated valves you can used a wheel lockout device, similar to those manufactured by Master Lock or Brady. They are designed to encapsulate the wheel of the valve thereby blocking access to the wheel and preventing operation. They come in a range of five sizes; the largest can cover a wheel of 350mm (14”) diameter. The wheel cover is secured in place using a safety padlock. Users can choose between four different colours to denote the process medium or perhaps the valve positional status.
If the valve wheel you need to lock is larger than 350mm, you can consider a cable lockout or padlock and chain. These work by threading the cable or chain around the rim of the valve and through the bonnet or perhaps a piece of adjacent pipe work or steel work.
Locking a lever operated valve can be slightly more challenging. The problem with lever operated valves (ball valve, plug valve, butterfly valve) is that they vary greatly from one manufacturer to another. The topworks design of the valve is rarely the same and this means that the locking device may not engage securely on the valve. To resolve this, Master Lock has developed an innovative lockout known as the Seal Tight™ valve lockout. It works by removing the valve lever and locking it away in a pouch which is wrapped around the body of the valve. Some valve locking devices can only lock the valve in a single position, usually the closed position.
Other valve lever lockouts work by attaching to the lever and physically blocking the turning movement of the valve.
Actuated valves.
If your valve is actuated, locking it off can actually be quite straight forward. For an electrical actuator, the device will have an on/off switch on board. The switch often has a padlock facility which can be used to secure the switch in the ‘off’ position.
For pneumatic or hydraulic actuated valves, blocking the flow of air or oil to the actuator will disable it. This can be done with a small diameter ball valve in the flow line. This valve can then be locked out with one of the lever locking devices described above.
On a note of caution, changing the operational function of actuated valves in this way should only be done in consultation with qualified process engineers.
Locking device integrity
At the start of this article we stated that there are two factors that determine which type of locking device is needed. However, you might like to also consider a third factor. That is the degree of protection against inadvertent operation. Let’s expand on this point.
Inadvertent operation could be regarded as accidental operation, deliberate procedural violation or vandalism.
If the location of the valve makes it a target for vandalism, this must be taken into consideration. In this scenario, a risk assessment should be undertaken. If the consequences present a risk of injury or death, then a high integrity locking device is needed. Equally, if the consequences of operation could result in a high cost loss, these circumstances may also lead you to consider a high integrity locking device.
So what is meant by a high-integrity locking device? This type of device, (normally referred to as an interlock) is very difficult to remove from the valve in as much as specialist tools would probably be needed. It would also be highly tolerant to abuse and attempts to defeat or override.
The device can be locked in both open and closed positions with a separate key corresponding to each locked position. Valve interlocks are often used in a set of multiple valve locks whereby the sequence of operation of a number of valves can be pre-determined through the coding of the keys.
So whether you are simply locking off a valve during a maintenance procedure or implementing sequential control over a number of valves, there is suitable device available.
Total Lockout (Safety) Ltd have produced a useful valve locking device selection guide to help you produce the right solution.
Ends…
Total Lockout (Safety) Ltd is a distribution and supply company specialising in lockout tagout systems. The company was formed in 2010 by Tim Hughes who has over 20 years’ experience in specifying industrial and process safety locking systems.
No comments:
Post a Comment