The water is all contained within the system and without suitable control it can manifest as liquid water and present problems throughout the system. However, with a higher input temperature the ambient air is capable of holding a significantly larger amount of water vapour. Pressure dew point temperatures are further elevated leading to more water being liberated in the parts of the compressed air system closer to the compressor, i.e. This graph shows the effect of a higher ambient air temperature. The graph below gives some indication of this temperature relationship. The situation is slightly improved if instead of operating at 25 the temperature of the ambient air is higher. Also in general there would be much more water vapour available which could be turned into liquid water. It should be obvious that ambient air with a higher realtive humidity would make this effect more likely. This is proably the reason why, on some humid days, the water traps and drains on a system seems to overflow and exhaust very quickly. It is only further down the system, where the air has had time to cool further, that the majority of the water will be liberated. In some high-use conditons, where the temperature of the air at the reciever has built up to temperatures above the pressure dew point, no water will be liberated for the water vapour leaden air. Looking at the curves more closely it is also possible to postulate as to why, under some high-usage conditions, that water is can be liberated in such large quantities downstream of the receiver – near the tools and processes for which the air is used. It can be clearly seen that even when mildly humid air is lightly compressed liquid water is produced. The ratio of water vapor partial pressure p v to water vapor pressure p s in saturated wet air with the same temperature is known as relative humidity, which is represented by. The graph shows this relationship for four value of ambient %RH, (50,60,70 and 80%). This graph provides an indication of the relationship between the pressure dew point temperature and the amount of compression the ambient air has been subjected to.
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