FEATURE PUMPS, VALVES & ACTUATORS
PEEK PERFORMANCE - OFFERING THE BENEFITS OF METAL AND PTFE
There are many contributors to poor temperature control across the process industries, with experts saying a different approach to control valve specification could lead to improvements. Darren Silverthorn, National Controls and Metering specialist at Spirax Sarco, explains why soft seats, particularly PEEK solutions, can potentially deliver benefits in demanding food and drink manufacturing environments
T
he wonderful world of engineering presents industry with plenty of
options when it comes to materials and components, and their ensuing benefits, such as improved uptime productivity and energy efficiency, as well as reduced costs. Selecting the right solution for your business can be daunting, and defaulting to the familiar isn’t uncommon. However, alternatives exist that can make improvements you didn’t know were possible. So, let me explain. Minimising product
higher the number, the lower the leakage. Different plug and seat materials are used to achieve the required leakage rate with metal typically used for class IV and soft materials like Polytetrafluoroethylene (PTFE) used for class VI. Metal seats and plugs tend to be the
‘PEEK has
wastage and spoilage is a key challenge in the food and drink industry. Many companies in the sector operate near maximum capacity, so process uptime is key. Poor temperature control can result in product spoilage, product burn-on and increased CIP (clean-in-place), which is a major frustration. Many don’t realise poor temperature control is often caused by control valve leakage and can be identified by these symptoms. However, the problem’s origin isn’t always obvious, and this is where control valve specification has a lot to answer for. Reduced leakage leads to better process control, and could negate the need for additional components like automatic isolation valves. Let’s go on to explore control valve leakage classifications.
proven itself in more
abrasive, hotter areas and is becoming the challenger material to consider’
default for food and drink applications as they are produced in various stainless- steel grades, of which the benefits are well-understood. However, with a metal seat and plug it is not possible to achieve class VI leakage. Generally, the softer the material, the better the
prevention of
leakage, therefore for class VI leakage,
materials such as Polytetrafluoroethylene, or
PTFE are used. But these materials generally tend to be less robust and therefore more prone to damage. As an engineer in the food and drink
industry, you most likely know of PTFE – a common example of a fluoropolymer material used for its sealing properties, low friction coefficient and chemical resistance. Although recognised for these properties, PTFE is restricted by its maximum operating temperature and robustness – both important considerations for steam-using applications. For these reasons, many default to
BEST IN LEAKAGE CLASS Class leakage refers to the leakage classifications defined by ANSI FCI 70-2 – an industry standard followed by control valve manufacturers. For globe valves, it defines the leakage amount allowed between the plug and seat when the valve is closed. The most common leakage classes are class IV and class VI, and the
more robust and commonly used materials such as stainless steel, and prevent increased leakage by installing automatic isolation valves. A more sophisticated PEEK solution has evolved in response to this, presenting an opportunity for food and drink manufacturers looking to enhance their process control. PEEK – or PolyEtherEtherKetone if you
24 DECEMBER 2019/JANUARY 2020 | PROCESS & CONTROL
The Spira-trol control valve is designed to meet the demands of today’s industries
want to get scientific – combines exceptional wear, chemical and heat resistance with the ability to provide class VI leakage. It can be continuously exposed to fluid temperatures up to 250°C and a maximum differential pressure of 19 bar. Working with steam, you need to know
that the components responsible for controlling it are completely reliable – these properties show PEEK can provide the reassurance required with the combined benefits of metal and PTFE seats discussed here, without compromise.
FROM THREE TO TWO In specifying a PEEK seat to reduce leakage and provide better process control, you also remove the need for additional automatic isolation valves. Yet a dedicated isolation valve is always needed for safety and maintenance, so essentially you would be reducing from three valves to two. This reduction can be made without compromise on safety by using double block and bleed isolation valve units, such as Spirax Sarco’s SafeBloc. By doing so, maintenance and process
managers not only remove the additional valve’s upfront cost, but also ownership costs via maintenance, compressed air or electricity consumption. By increasing your process’s reliability, you can enjoy peace of mind knowing leakage is much less likely to occur, reducing ensuing product spoilage and downtime effects. With steam being crucial to food and
drink processes, it’s easy to see why metal has been the go-to choice over PTFE. However, with PEEK having proven itself in more abrasive, hotter environments adhering to specific regulations, it’s really becoming the challenger material to consider. I would urge anyone responsible for control valves in these sectors to find out more.
Spirax Sarco
sxscom.uk/food_drink
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