The best metal butterfly valve lining for demanding media?

Figure 1 – Special design liner support

Figure 2 – Special design shaft seal

Lining a metal butterfly valve with a thermoplastic material, typically a fluorocarbon, means that media does not come into contact with any metal parts. This is particularly useful where corrosive liquids are being handled – for example, effluent, sludge or corrosive chemicals.

Thermoplastic liners are also chemically inert. This is useful where high purity media is required, for example in pharmaceutical and semiconductor high purity water applications.

Common valve lining materials
The main lining materials used for metal valves are:
• PTFE (PolyTetraFluoroEthylene)
• PFA (PerFluoroAlkoxy)

PTFE liners are isostatically compression moulded from sintered chips. PFA linings are melt-processible which provides a far less permeable liner that can also be precisely moulded. TFMTM PTFE incorporates a PerflouroPropyl Vinyl Ether (PPVE) modifier to the PTFE. This is a more advanced material which has the following improvements to PTFE.

• Reduced cold flow by factor of 3
• Firmer polymer structure
• Less permeable (factor 2) for chemicals and gases
• Weldable
• Smoother surface for machining
• More transparent
• Injection mouldable in special cases

The advantages of PFA and TFMTM lined butterfly valves are that they:

• work well with most corrosive media to protect metal butterfly valve parts
• can outperform more expensive alloy valves
• are suitable for multiple-product processing lines being unaffected by media changes
• are seldom affected by process temperature variations • are virtually impermeable

PFA and TFM Lined butterfly valves
GEMÜ 490 series lined metal butterfly valves are available with a moulded PFA or TFMTM body liners. These linings are achieved using the latest plastic injection moulding machines to form a precise lining locked to the valve body. This is integral to the valve’s corrosion resistance.

Special silicon backing
As can be seen in Figure 1 the valve body liner is backed by a specially design silicon rubber backing which provides the forces needed for effective media sealing downstream.

Special shaft seal system
Chemical handling requires specialist sealing to prevent leaks to atmosphere. A special 4 fold shaft seal system (Figure 2) is also incorporated to prevent dangerous media leaks.

GEMÜ 490 series key features and benefits:-
• High performance PFA or TFMTM lined metal butterfly valve
• Wide range of sizes from DN40 to DN900 (1½″ – 36″)
• PN3/10/16 bar media rated (depends on size)
• Suitable for use with temperatures up to +200 degrees Celsius
• Pneumatic, Motorised, Manual and bare shaft options
• Ideal for the distribution of Corrosive Chemicals, Effluents and Slurries
• The valve of choice for High Purity water applications in API Pharmaceuticals and Semiconductor plant

Tel: 01925 824 044

Published in Valve User Magazine Issue 50

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