WHAT VALVES ARE USED
At first glance, it might appear that
virtually any type of shutoff valve would
work, but a closer look at the operating
conditions provides a broader picture.
These outlet valves, which are releasing
water, are doing so at huge volumes,
relatively high head pressures and at a
resulting high velocity. The combination
of output flow conditions can result in
severe damage from cavitation at the
valve outlet. This phenomenon can
rapidly destroy many types of valves, so
measures to abate the cavitation must
be taken either in valve selection or
piping design.
During the early part of the 20th century, standard valve types such as gate
and globe valves were given this flow
control job. But the effects of cavitation
destroyed them at an alarming rate. As
a result, engineers looked at new valve
designs, such as the Larner-Johnson
needle valve, to solve the problem. Other
solutions were also tried, included forcing air into the downstream flow of
standard valve types to keep cavitation
from occurring.
The needle valves, however, have
done a good job for many decades, yet
newer designs have now replaced many
of those work horses. Both fixed-cone
and jet-flow gate valve designs are now
used in such applications and are
currently being retrofit into existing
structures as funds permit.
The fixed-cone, or Howell-Bunger
valve, is a simple balanced design that
requires little energy to open or close.
The outlet of a fixed-cone valve is very
similar to the outlet of a fireman’s hose
nozzle or a high-end home garden hose
nozzle, in that the high water pressure is
squeezed around the periphery of the
stationary cone by changing the position
of the circular seat that is inset in the
inside diameter of the moveable sleeve.
The flow is regulated by adjusting the
amount of water pressure introduced
into the chamber behind the cone via a
regulated water inlet.
The jet-flow gate valve looks like a
large fabricated slab gate valve, similar
to some API 6D designs. However, the
secret to its energy-dissipating success
is in the flow chamber of the valve. As
THD Heavy Duty Actuator
AC & C
Rack & Pinion Actuator
Pneum
TRIAC
• 100–
THD H
• 7,000
Stainle
Pinion
180º P
Electric Actuator
Electr
WE/XE
• 500-2
• Single
• Integr
• On/O
• Optio
Sprin
• Weath
ATEX
• AWW
(513) 247-5465
FAX (513) 247-5462
e-mail: sales@a-tcontrols.com
www.a-tcontrols.com
9955 International Boulevard
Cincinnati, Ohio 45246
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