THE NOBLE GLOBE VALVE
exists today. Control system designers
took the original globe valve and morphed it into an automatic regulating
device to solve fluid control issues in a
more productive manner. Initially these
pressure-regulating globe valves were
developed to control steam in boilers
and pumps. These early regulating
valves, also known as governors, are
now called control valves and are used
worldwide in virtually every industry
requiring fluid control.
The design of globe valves also is
very adaptable to services other than
regulating or blocking a handwheel or
actuator. If you take a standard globe
valve, remove its handwheel and yoke
bushing and replace those with a calibrated spring or counterweight, the
globe becomes a pressure relief valve. If
you remove that same handwheel and
yoke bushing and replace them with a
float and lever, it becomes a level control valve. And probably the most visible
globe valve adaptation is the fire
hydrant, which is a globe valve with the
handwheel and yoke bushing replaced by
a long extension tube and a fireplug hat.
SMALLER IS BETTER
Unlike some of the other valve designs
such as the gate and butterfly, the globe
is not commonly manufactured in very
large sizes. This is partly because the
large area of the disc acting directly
upon the stem creates a much greater
force than what is created for a gate or
other on-off valve of the same size.
Larger globe valves operating at high-differential pressures almost always
require some mechanical assistance to
close under pressure, usually in the form
of a manual or motorized gear operator,
or in some cases, a hammer-blow handwheel. Due to the large surface area of
the valve disc and the pressure exerted
on the disc from below, large, low-pressure globe valves require additional
strength in bonnet designs to keep them
from flexing and leaking past the seats
while in the closed position.
While very large globe valves are not
common, small globe valves that fit in
the palm of your hand are. These small
valves, usually manufactured from solid
Figure 4. Y-pattern pressure-seal globe valve
barstock, are used extensively for
instrument valves in scientific environments, fluid sampling applications, or
anywhere that small-diameter, fluid regulation is required. Many are needle-disc types and provide very precise flow
control. Some are also fitted with various tubing connections to allow easy
connection to tubing lines. While most
globe valve stems are of the rotating
type, some have non-rotating stems to
lessen the possibility of stem galling.
The majority of globe valves are
designed for regulating flow, but some
specially designed, high-pressure, Y-pattern types are adept at tightly sealing
fluid flow in block or on-off service.
Because the disc moves down directly on
the seat, the thrust on the stem is transferred directly into the seating force.
This allows virtually all the actuator
output force to be used for sealing the
valve against leakage. Most often, these
high-pressure globes are built with pressure-seal instead of bolted bonnets. The
pressure-seal bonnet increases its seala-bility as the internal fluid pressure
increases.
Globe valves typically have a preferred flow direction, which is usually
confirmed by an arrow stamped or cast
into the outside of the valve body. For
most general plumbing and industrial
applications, the primary flow direction
is upward against the disc. This upward
flow is smoother on and around the disc,
and it provides free rotation of the disc
on the stem, which allows the valve to
find its proper seat or “fit” when closing. In some applications, such as high-
