Mechanical seals often need to be used in chemical applications. When confronted
with some harsh chemicals, mechanical seals containing elastomers made of Viton, Kalrez
or Chemrez can't hold up. Because PTFE (polytetrafluoroethylene)or as most people know
it Teflon ® , has a 0-14 ph range it usually will hold up.
Like most materials every choice has an up and a down side. PTFE will handle
most chemical applications, chemical attack is no longer an issue. On the down side PTFE
wedges can cause fretting of your sleeve or shaft if you have not hard surfaced your shaft or sleeve (plasma coating).
The stationary element of your seal will require a PTFE gasket. It's not much good
to have a PTFE on the rotary and then use an elastomer on the seat. We have seen it done,
and because it is a static application some have gotten away with it, but it is not
recommended. Most commonly the seat will be a L-shaped or Clamped mount
style to allow space for a PTFE gasket to be used as the secondary sealing
element.
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