put signal or position switch to give the
operator field visibility.
Certain steps can be taken to maximize the accuracy of the temperature
application. Considerations in regards
to that issue include the temperature
range of the actuator, the stroke length
of the valve (a shorter stroke requires
less fill fluid phase change to stroke the
valve, thus improving performance),
and the installed flow capacity (Cv) in
the valve body.
Additionally, many manufacturers
offer piloted temperature regulators
that provide reduced temperature spans
and, in many cases, larger line sizes for
higher flow rates.
STEAM TRACING
Stories abound of burst water lines
that occur when plants experience an
early freeze. This often results from
steam tracing lines not used because
an operator either fails to open the
necessary steam tracing valves or is
not aware of a weather forecast. Fortunately, products are available that can
eliminate this issue.
With steam tracing water lines,
both the bulb and capillary often can
be eliminated and the actuator allowed
to simply measure and react to the
ambient temperature. Using the example of the burst water line above, an
operator could set the temperature
regulator for 40° F ( 10° C), thus ensuring the valve will begin to open once
the temperature drops below that setting. Once the valve opens, steam will
begin to flow to the tracing lines, minimizing the risk of freezing the water
within the piping. Such valves not only
reduce the likelihood of human error,
they also provide dramatic utility cost
savings. The same valve that opens at
40° F ( 10° C) will then close as the
ambient temperature rises above that
level so costly steam will not be
allowed to flow into tracing lines when
not needed.
As with any industrial product, quali-
ty and accuracy of temperature regula-
tors varies from manufacturer to manu-
facturer. When selecting a valve for this
purpose, considerations should be:
; Is the thermal system fully sealed
and replaceable?
; What is the manufacturer’s stated accuracy?
; What “real world” accuracy can
be expected?
; Is the application suitable for a
commercial or industrial valve?
SENSING ELEMENTS
Numerous sensing bulbs are also available and can be tailored specifically to
the application to increase accuracy.
Finned bulbs (Figure 2), for example,
offer greater surface area (and thus
sensitivity to temperature changes) and
typically are applied on duct applications to control heating, cooling or
humidity within a structure.
“Dead zones” toward the capillary
end of a bulb often are used to ensure
temperature reading is in the desired
area of a tank or vessel (Figure 2).
Many customers will use a thermow-ell to facilitate installation and maintenance tasks.
INSTALLATION AND
MAINTENANCE
Understanding the cost advantages of a
self-contained temperature valve is
easy—both at the component level and
with installation labor costs. What’s a
little more complicated is troubleshooting issues. When a temperature control
failure in a control loop occurs, multiple
devices may be responsible and troubleshooting involves seeking out the
component causing the error. If a
mechanical valve is used, an operator
simply checks the setpoint on the valve
for accuracy. If that setpoint is correct,
the thermal system is tested. Components not working correctly can be
replaced. If testing proves the valve is
functioning, the heating/cooling fluid
supply is checked.
CONCLUSION
Mechanical temperature regulators can
provide a cost-effective and reliable
means to control temperature. When
they are appropriate for an application,
they also can simplify maintenance and
reduce both installation and operating
costs. VM
Figure 2—Finned bulb (top) and dead zone (bottom)
TIM GAINER is a regional manager for Jordan
Valve ( www.jordanvalve.com) in Cincinnati,
OH. He has been part of the Jordan Valve team for
over 15 years and has nearly 20 years of control
valve and regulator experience. Reach Gainer at
tgainer@richardsind.com.
