Figure 15-9.--Cross-sectional view of a gate stop valve rising
Figure 15-10.--Butterfly-type valve.
usually have a pointer or a gauge to indicate whether
the valve is in the open or closed position. Some gauge
To close the valve, turn the handle a quarter of a
valves have rising stems. In these valves, both the gate
turn to rotate the disk 90. The resilient seat exerts
and stem will move upward when the valve is opened.
positive pressure against the disk, which assures a tight
In some rising stem valves, the stem will project above
the handwheel when the valve is opened.
You will find that butterfly valves are easy to
maintain. The resilient seat is held in place by
mechanical means. Therefore, neither bonding nor
The butterfly-type valve (fig. 15-10) in certain
cementing is necessary. Since the resilient seat is
applications has some advantages over gate and globe
replaceable, the valve seat will not require any lapping,
valves. The butterfly valve is lightweight, takes up less
grinding, or machine work.
space than a gate valve or globe valve, is easy to
Butterfly valves serve a variety of requirements.
overhaul, and can be opened or closed quickly.
These valves are now being used in freshwater,
The design and construction of butterfly valves may
saltwater, JP-5 fuel, Navy special fuel oil, diesel oil, and
vary, but a butterfly-type disk and some means of
lubricating oil systems.
sealing are common to all butterfly valves.
The butterfly valve shown in figure 15-10 consists
of a body, a resilient seat, a butterfly-type disk, a stem,
Check valves permit liquids to flow through a line
packing, a notched positioning plate, and a handle. The
in one direction only. For example, they are used in
resilient seat is under compression when it is mounted
drain lines where it is important that there is no
in the valve body. The compression causes a seal to
backflow. Considerable care must be taken to see that
form around the edge of the disk and both upper and
valves are properly installed. Most of them will have
lower points where the stem passes through the seat.
an arrow, or the word INLET, cast on the valve body to
Packing is provided to form a positive seal around the
indicate direction of flow. If not, you will have to check
stem if the seal formed by the scat is damaged.