TYPES OF 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
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
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
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.