The In-line Shutoff Valve is the perfect choice for situations where you need absolute dead tight shutoff.  The valve has a raised seat so there is no pocket in the line.  Other valves have a recess in which product can puddle and degrade.  The raised seat makes it so the line is completely drainable on either side of the seat.  Combine a line drain with the In-line Shutoff Valve and you have a perfect combination for polymer shut down.   This design uses the plunger seal so it can be used in high temperature / high pressure processes including 2500# @ 1000F.  Available in either full port or reduced port designs.