As water first enters the drinking
water system and into the pump
station, it passes through four
potentially different types of valves:
ball, check, gate, butterfly—the
workhorse valves of the entire system.
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provide complete 100% shutoff. The
ball valve, along with the butterfly
valve and plug valve, are part of the
family of quarter-turn valves. Ball
valves are durable and usually work to
achieve perfect shutoff even after years
of use. For this reason, they are an
excellent choice for shut-off applications (and are often preferred to gate
valves for this purpose). They offer the
fine control that may be necessary in
throttling applications, superior to a
check valve or a gate valve.
Check valves, by design, allow flow
in only one direction and are generally
used in the pump control application.
These valves allow water to move in
only one direction—into the pump station or treatment plant to be treated
and then out into the rest of the system.
Reverse flow produces the effect of having the valve close. Check valves are a
common and inexpensive means of
pump control and can be used in both
water and wastewater applications.
Gate valves are the most common
type of valve found in water distribution
systems and live up to their name. They
are the gatekeepers of the system and
are designed to be either fully open or
closed. The gate, or wedge, of the valve
is raised and lowered by a stem or
screw, which is operated by a hand
wheel or valve key. When fully open,
gate valves provide almost unrestricted
flow because the gates are pulled fully
out of the water path.
Butterfly valves can be either
modulating or open and closed, with
varying levels of openness, which make
them a suitable choice over gate valves
for modulating applications and filtration. Each butterfly valve consists of a
body in which a disk rotates on a shaft
to open or close the valve. Because the
disk of a butterfly valve stays in the
water path when in the open position,
the valve creates a higher resistance to
flow than a gate valve. Butterfly valves
are flow control devices and are often
used in the filtration process and to prevent backflow of water into the system.
As water leaves the treatment facility and travels throughout the rest of the
water distribution system, it flows