Reference Manual

10B −19
valves are on/off valves but are usually
equipped with positioners so that they can be
used as backup flow control valves.
Control Valve Selection
The following charts list Fisher valve selections for
a typical Kamyr process. Control valve metallurgy
has usually been 316 SST except for some valves
on the bleach plant. On the C/D, D1 and D2
extractions and stock flow to these stages, the
valves are usually titanium and sometimes 317
SST. More recently, the use of carbon steel valves
on steam and some filtrate service has been
considered. Metal seated ball valves are used
where the service requires a scraper seat (HD
design) such as white liquor and cooking
circulations on the digester. Metal seats are also
sued on throttling service that have high pressure
drops where the metal seat is more resistant to
erosive wear at the resultant high velocity. The
heavy duty butterfly valve (Special 8500) is used
almost exclusively for digester circulation
switching. The main features of this valve for this
service are the stellite bearings, double packing,
and extra heavy design shaft. There are no seats
in this valve so that it will not jam due to scale
buildup. It is also sometimes used on throttling
service where tight shutoff is not required, but
where there is a scaling tendency. The history of
valve selection has not been determined solely by
the process requirement but in many cases by
what valve technology was available at the time.
The choice is sometimes limited due to Kamyr’s
requirement for flanges on all except butterfly
valves.