What happens in cold pipework
If pipework temperature falls below the dew point corresponding to local pressure, condensate may form. The relevant temperature is therefore not only at the dryer outlet but also at the coldest point along the entire path. Allow a suitable margin for fluctuations and measurement uncertainty.
Do not confuse pressure and atmospheric dew points
When air expands without a change in composition, water vapour partial pressure and dew point fall. A sensor downstream of pressure reduction may therefore show a much lower value than one in the main distribution system. Moisture has not necessarily been removed; the measurement conditions have changed.
What to check in practice
- Determine the lowest temperature the air will encounter along its path.
- Record pressure at the sensor and the sampling method.
- Assess the dryer at the worst combination of flow and inlet temperatures.
Example scenario
The air has a dew point of +3 °C at distribution pressure. If it passes at approximately the same pressure through pipework cooled to −5 °C, there is a risk of condensation and subsequent freezing. A refrigerated dryer with that dew point alone therefore does not solve such winter pipework conditions.
What to watch out for
- Comparing atmospheric dew point with the temperature of pressurised pipework.
- Measuring in an unflushed branch with different conditions.
- Treating dry-looking pipework as proof of an adequate dew point.
Is the lowest possible dew point always better?
A lower value can increase treatment energy and maintenance costs. The goal is to reliably meet process needs and temperature conditions, not to dry unnecessarily to the lowest technically achievable value.