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.
Other advantages
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.