FOOD & BEVERAGE
C
ontrol valve leakage is a major contributor to poor temperature control across process industries. However, a different approach to control valve specification could yield significant improvements. Darren Silverthorn, national controls and metering specialist at Spirax Sarco explains why PEEK soft seats can hugely benefit food and drink manufacturers.
Correctly specified control valves greatly
improve uptime, energy efficiency and productivity in industry, while reducing costs. Choosing the right solution for your process can be daunting, and without knowledge of alternatives that offer improvements, defaulting to familiar options is common and understandable. So, let me explain what improvements are possible.
common leakage classes are class IV and class VI – the higher the number, the lower the leakage. Different plug and seat materials can achieve the required leakage rate, with metal typically used for class IV and soft materials like PTFE used for class VI.
THE APPEAL OF SOFT SEATS Metal seats and plugs are often the default for food and drink applications as they are produced in a variety of stainless-steel grades, of which the benefits are widely understood across all
exceptional wear, chemical and heat resistance. It can be continuously exposed to fluid temperatures up to 250°C and a maximum differential pressure of 19 bar. Components responsible for controlling steam must be completely reliable – these properties show PEEK is, and combines the benefits of metal and PTFE seats previously discussed, without compromise.
industries. However, metal seats and plugs cannot FROM THREE TO TWO achieve class VI leakage.
In general terms, the softer the material, the better the prevention of leakage therefore for class VI leakage, materials like Polytetrafluoroethylene
LOSING TEMPERATURE CONTROL (PTFE) are used. However, these materials tend to Minimising product spoilage and wastage is a key challenge in the food and drink industry. With many companies in the industry operating near maximum capacity, 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. Poor temperature control is often caused by control valve leakage, and can be identified by these symptoms. However, the problem’s root cause isn’t always obvious, which is why control valve specification is key. Reducing leakage results in better control while also negating the need for additional components like automatic isolation valves.
BEST IN LEAKAGE CLASSIFICATION Class leakage refers to leakage classifications defined by ANSI FCI 70-2 – an industry standard for control valve manufacturers. For globe valves, it defines leakage amounts allowed between the plug and seat when the valve is closed. The most
20 DECEMBER/JANUARY ANUARY 2020 | FA
be less robust and more prone to damage. As an engineer operating within the food and drink industry, you might be familiar with PTFE – a common example of a fluoropolymer material used for its sealing properties, low friction coefficient and chemical resistance. Although recognised for the properties mentioned above, PTFE is restricted by its maximum operating temperature and robustness. Both are important considerations for steam-using applications. Consequently, many will default to more robust, commonly used materials like stainless steel, and prevent increased leakage through installing automatic isolation valves. A more sophisticated PolyEtherEtherKetone (PEEK) solution was
developed in response to this, giving food and drink manufacturers a huge opportunity to enhance their process control.
WHAT IS PEEK? PEEK provides class VI leakage while offering FACTORY&HANDLINGSOLUTIONS ORY&HANDLINGSOL UTIONS
Specifying PEEK seats to reduce leakage and improve process control removes requirements for additional automatic isolation valves. Although, it’s important to remember that a dedicated isolation valve is always needed for safety and maintenance, so essentially you would be reducing from three valves to two. This can be done without compromising through using all-encompassing double block and bleed isolation valve units, such as Spirax Sarco’s SafeBloc solution.
By doing so, maintenance and process managers remove the additional valve’s upfront costs and subsequent maintenance, compressed air or electricity costs. Improving process reliability means minimal chance of leakage, reducing the resulting effects of product spoilage and downtime. In conclusion, with steam crucial to many food and drink processes, it is understandable why metal is preferred to PTFE. However, with PEEK able to function more abrasive and higher temperature environments adhering to specific regulations, its status as a challenger material for the industry’s maintenance and process engineers is assured.
Spirax Sarco
www.spiraxsarco.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62
