How the Posi-Pressure Control System Works
A normal steam system may modulate into a vacuum to control
temperature. A vacuum breaker is often installed to prevent this
condition. Once the vacuum breaker opens, temperature control is
accomplished by mixing air with the steam. The steam/air mixture results
in a lower temperature. However, even a vacuum breaker will not work if
condensate must be elevated to an overhead return, or if the return
system is pressurized.
The Posi-Pressure Control System acts as a vacuum
breaker. Instead of introducing air at atmospheric pressure, the
controller injects air at an elevated pressure. The user presets the
level of elevated air pressure at the time of installation. Rather than a
specific pressure, the controller maintains a specific differential
pressure across the steam trap. Even if a steam trap fails or other
causes change the condensate return pressure, the controller will sense
the difference and maintain the preset differential.
Minimum air usage
The Posi-Pressure Control System uses very little
air. The amount depends upon the size of the steam trap selected. Air
usage can vary from as little as 10 SCFH to 90 SCFH (0,3 to 2,5 Nm3/h)
or more on large systems. To put this in perspective, a 27 SCFH parcel
of air amounts to a 3-foot cube in one hour. Once the initial air is
introduced, only the leakage through the large vent bucket in the steam
trap must be considered. This air volume is so low that it is
practically undetectable in a deaerator.
Float and thermostatic traps are generally
recommended for use on modulated steam systems because they drain better
when there is no motive pressure other than the static head of
condensate. With a positive pressure always being maintained by the
Posi-Pressure Control System, an inverted bucket steam trap with its
inherent longer life expectancy can, and must, be used. Since air is
injected at a positive pressure, carbon dioxide (the real cause of
corrosion) is diluted and swept clear of the heat exchanger.