FOCUS Chemicals & Pharmaceuticals
The importance of chemical
compatibility for control valves Kieran Bennett, Field Segment Manager for Hygienic – Food & Beverage applications at Bürkert, explains how control valves should be properly matched to the chemicals they come into contact with
A
signifi cant change increasingly seen in the valve market, particularly for hygienic applications, is the focus on
the chemical composition of the materials used in valve construction. Today, perhaps half of all users of process valves require a materials certifi cate, while nearly all diaphragm valve users consider it a necessity. In some cases, such as the pharmaceutical sector, every valve that comes into contact with the media requires full documentation and traceability. This increased requirement is unsurprising: not only does it give the customer reassurance, but it answers increasingly strong regulatory compliance. In sectors such as food and beverage and pharmaceuticals, whether for on-site check or compliance with FDA regulations, a valve user must prove the chemical composition. For the manufacturer of a PTFE diaphragm valve, for example, this means proving traceability to the original batch of manufacture of the chemicals and the quantity used.
Valve bodies
The chemical composition of the valve, mainly consisting of its body, seal and potentially the diaphragm that creates a barrier with the media, is an important factor for the quality and safety of the end product. Food and beverage manufacturers, for example, need to prove that there’s no shedding of traces of valve components, which can contaminate or impact the taste or odour of the product.
Valve material specification should include resilience to the chemicals it will be in contact with
Electro pneumatic ball valve
This means that clarifi cation of the valve’s chemical composition is fundamental, as well as its suitability for long-term use with the media it comes into contact with. The other main concern in valve material
specifi cation is resilience to the chemicals it comes into contact with in order to achieve the expected lifetime. For this reason, proving origin is also an important factor for customers to validate valve quality. For example, a manufacturer can be asked to provide a 3.1 material certifi cate, which could trace the composition of a stainless steel valve body to clarify carbon content. Lower quality valves can use stainless steel with a higher carbon content, generally making it more brittle and less robust, so validation is a sensible request.
Chemical compatibility Traceability is vital, but ensuring chemical compatibility can also be a matter of application experience. For example, in many dairies, nitric acid is used as part of the CIP (clean in place) process. Within a ball valve, typically two carbon graphite seals are used in the end caps; however, the material isn’t suitable for long-term use with nitric acid, which will degrade the seals, reducing the number of cycles the valve can perform in its lifetime. This is a commonly overlooked example and instead Bürkert would use an angled seat valve with a PTFE seal, suitable for use with nitric acid and ensuring that it can
24 December/January 2021 | Automation
achieve its seven million cycle lifetime. It is important to select the body and seal materials most eff ective for use with the chemicals in each specifi c application. PTFE is commonly used for seals, diaphragms, as well as valve bodies. Resistant to nearly all chemicals, including acids and alkalis, PTFE is an ideal choice for CIP applications. Its carbon-fl uorine bonds make it inert and therefore ideal for use with reactive and corrosive chemicals. It is, however, susceptible to cold fl ow, which is distortion under stress of high temperatures or temperature fl uctuations. Advanced PTFE can instead be specifi ed if the application includes extreme temperature changes or frequent sterilisation.
Alternatively for diaphragm use, GYLON is a third generation PTFE, used across the widest range of applications. With increased resistance to stress, it can be used with greater fl uctuations in temperatures as well as higher temperatures, and has a longer lifetime. EPDM is also frequently used for diaphragms and seals because of its resistance to ozone and hot water, as well as FKM which is often selected for its resistance to oil. Valve bodies are frequently brass or stainless steel, or a suitable hard plastic variant with suffi cient impact resistance. Polypropylene and polyethylene are commonly selected for their resistance to various organic solvents, acids, bases and salts while polyamide is appropriate for use with greases, oils, waxes and fuels. Meanwhile, PPS is ideal for use in high temperatures above 200 degrees centigrade.
The chemical composition of the valve components and the media fl owing through it are critical factors for a wide range of applications. The challenge can be complex so engaging the right application expertise is well advised.
CONTACT:
Burkert Fluid Control Systems
www.burkert.co.uk
automationmagazine.co.uk
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