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Lift  Check  Valves
Butterfly  Check  Valves

Mechanical Science Volume 2 of 2
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TYPES OF VALVES DOE-HDBK-1018/2-93 Valves Flow to lift check valves must always enter below the seat.  As the flow enters, the disk or ball is raised within guides from the seat by the pressure of the upward flow.   When the flow stops or  reverses,  the  disk  or  ball  is  forced  onto  the  seat  of  the  valve  by  both  the  backflow  and gravity. Some  types  of  lift  check  valves  may  be  installed  horizontally.    In  this  design,  the  ball  is suspended by a system of guide ribs.  This type of check valve design is generally employed in plastic check valves. The  seats  of  metallic  body  lift  check  valves  are  either  integral  with  the  body  or  contain renewable seat rings.   Disk construction is similar to the disk construction of globe valves with either metal or composition disks.   Metal disk and seat valves can be reground using the same techniques as is used for globe valves. Piston  Check  Valves Figure 25   Piston Check Valve A piston check valve, illustrated in Figure   25,   is   essentially   a   lift check   valve. It   has   a   dashpot consisting of a piston and cylinder that  provides  a  cushioning  effect during  operation.   Because  of the similarity  in  design  to  lift  check valves,   the   flow   characteristics through  a  piston  check  valve  are essentially  the  same  as  through  a lift check valve. Installation is the same as for a lift check  in that  the  flow  must  enter from under the seat.   Construction of  the  seat  and  disk  of  a  piston check valve is the same as for lift check valves. Piston  check  valves  are  used  primarily  in  conjunction  with  globe  and  angle  valves  in  piping systems experiencing very frequent changes in flow direction.   Valves of this type are used on water, steam, and air systems. ME-04 Rev.0 Page 38







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