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.
So what are the best liners for the job?
The main lining materials used for metal valves are:
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.
TFM™ PTFE incorporates a PerflouroPropyl Vinyl Ether (PPVE) modifier to the PTFE. This is a more advanced material which has the following improvements to PTFE:
The advantages of PFA and TFM™ lined butterfly valves are that they:
GEMÜ 490 series lined metal butterfly valves are available with a moulded PFA or TFM™ body liner. 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.
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.
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.