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 combination of liquid and vapor. I n operation, temperature changes at the
b u l b produce expansions or contractions of the medium filling the system,
w h i c h in turn causes expansion or contractions of the bellows. The movement
o f the bellows is transmitted to the valve disk by means of the valve stem.
The expansion movement of the bellows is opposed by an adjustable compression
spring.
The controlled temperature can be adjusted by changing the spring
compression.
6 . 2 . 2 Remote Control. Remote control of temperature may be affected by a
d i a p h r a g m - o p e r a t e d valve similar to that shown in figure 6-13. With this type
o f valve, signal air pressure from a pneumatic transmitter is applied in the
top chamber over the diaphragm. T h e air loading pressure changes in relation
t o temperature changes of the controlled medium, thereby operating the valve
t o control the flow as required.
6 . 3 M o i s t u r e C o n t r o l . E n e r g y conservation, prevention of pipe corrosion, and
r e d u c t i o n of insulation deterioration are possible by remote sensing of
damaged insulation. T h i s is possible through wiring embedded in the
i n s u l a t i o n surrounding a pipe. When moisture comes in contact with the
e m b e d d e d wire, the electrical conductivity of the wire is changed. this
c h a n g e is sensed and transmitted to a central monitoring station. The
d i s t a n c e to the disruption Is displayed to maintenance personnel on a video
d i s p l a y and on a strip recorder simultaneously (figure 6-14). This timely
method of immediate detection of a remote insulation break minimizes a
d i s r u p t i o n of service normally associated with location and repair efforts.
6-18
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