FEATURE PUMPS, VALVES & ACTUATORS THE BUILDING BLOCKS OF SYSTEM SAFETY


Joe Bush, Swagelok product manager, explains the benefits of block valves, and how to achieve zero pressure and zero flow for the safer maintenance of industrial fluid systems


P


roactive, ongoing industrial fluid system maintenance helps ensure


that systems are performing safely, reliably and consistently – all top priorities for plant managers, no matter the industry. Safety must be considered when


performing such maintenance. Often, maintaining fluid systems involves swapping out gauges or changing measurement devices, tasks that can pose a risk to maintenance technicians if the line is under pressure. Isolating an energised line is the first


step in safely performing this kind of maintenance, and technicians must have a safe means of doing so. Some specific locations that often require an isolation configuration include: • All components or devices that require


regular maintenance or replacement, including filters, valves, or transmitters • Systems, skids, or lines requiring


repair, replacement, or reconfiguration • Sections of main process pipes that


require servicing or maintenance for any reason • Instrumentation lines that come off


the main process line (e.g., sampling systems or grab sample stations) • Lines carrying calibration fluids in


sampling systems • Sampling streams that may be


Figure 2: A bypass loop used to isolate a fluid system line allows the process to continue functioning while performing maintenance, which is essential if downtime is not an option


ALTERNATIVE ACTUATOR SOLUTION FOR LARGER VALVES


Kinetrol has increased its product portfolio with the introduction of the Model 60 actuator, which means the company’s torque output coverage is now to over 40,000 Nm (350,000 lbf.in). The Model 60 is currently the largest actuator in the Kinetrol collection, adding to the sixteen units


already available, starting at 0.1 Nm. The unit is a single vane actuator, giving ‘direct drive’ rotary control. The one moving part construction minimises side loading, eliminates axial loading and increases life expectancy. The Model 60 also utilises Kinetrol’s preloaded, double-opposed, polyurethane lip seal and air consumption reducing/energy absorbent side plate technologies. This, coupled with a new end-stop design, extends the actuator’s life, reduces its energy consumption and maximises its operating speed. As with their existing actuator range, the new Model 60 benefits


from Kinetrol’s modular concept of control accessories. This allows the customer to choose from a range of options such as the AP (pneumatic), EL (electropneumatic) and DP3 positioners, safe and hazardous area limit switch boxes and the company’s distinctive clock-type spring fail- safe packs. Compared to traditional actuator types of this size, Kinetrol’s Model


60’s output torque, in double acting applications, is uniform across its operating cycle, facilitating more optimal sizing and providing a compact solution. In addition, Kinetrol’s spring design, for single acting applications, results in much lower torque output losses - further enhancing compactness and eliminating spring fatigue failure. A technical data sheet for the new Model 60 is available on the website,


and will feature in the new catalogue, which was published in January. Kinetrol


www.kinetrol.com


switched on or off As such, it has become an industry


standard to include two sequenced block valves before individual legs in fluid system design, enabling technicians to safely bleed out target lines before beginning any maintenance procedures. During the upfront design process, most


engineers follow one of two common approaches. The first involves the engineer adding a third valve between the two block valves to bleed or vent runoff pressure that may be leaking from the first block valve. The second option involves a similar setup, here using the third valve to divert the flow to a bypass loop around the leg of the system that is undergoing maintenance. Each design strategy has its benefits.


Figure 1: The common double-block-and-bleed (DBB) configuration safely isolates fluid system lines for ease of maintenance


This article will describe design options that can help ensure safe system isolation and maintenance.


ISOLATION OPTIONS Double block valve configurations have become the industry standard for a few reasons. In a system with only one block valve – i.e., with no backup – even the smallest leak across the valve seat can mean that pressure will build slowly in the line undergoing maintenance, creating a potential safety hazard. Featuring two valves, a double block


configuration ensures that even if one of the valves leaks across its seat, the next valve will serve as a backup. A good valve should not experience seat leak, but it can happen under certain circumstances. For instance, if a line is outside, sun and heat may raise the system pressure beyond the valve’s specified rating. Poor maintenance over the long term can also cause a seat leak. It is also possible that the wrong valve has been selected for positive shutoff. To maintain safety, the following


configurations can be considered. Basic Double-Block-and-Bleed (DBB).


The double-block-and-bleed valve (Figure 1) is one of the most common isolation configurations, and for a good reason: it is simple and effective. It is usually used to transition from a process line to an instrumentation line when using a process interface valve, or on a line leading to a device or instrument – a transmitter, for example. The three individual valves that make up the DBB may be configured as a single unit manifold, or as three separate components in the system’s design. The Bypass Loop. This option (Figure 2)


is more complex than the DBB. But by rerouting flow, the bypass loop configuration has the additional benefit of enabling the process to continue functioning while technicians perform maintenance. This is a good choice for applications in which excessive downtime is not an option.


16 FEBRUARY 2020 | PROCESS & CONTROL 


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