Sušičky vzduchu tlakový rosný bod -40 °C
What a -40 °C dew point means and why it matters
A pressure dew point of -40 °C is one of the values most often required in compressed air treatment. It means the water vapour contained in the air only begins to condense at -40 °C (at the given working pressure). In practice, then, the air is dried so thoroughly that at ordinary ambient temperatures it remains entirely free of condensate. This dew point value is crucial for a wide spectrum of industrial applications, because it reliably prevents water condensing even in frost while not being as costly as more extreme drying to -70 °C. Many standards and recommendations (ISO 8573-1 class 2 for water content, for example) cite exactly -40 °C as the requirement for compressed air quality for sensitive equipment and processes. As a result, a -40 °C dew point has become the de facto industrial standard for „very dry“ air, suitable even for outdoor pipework exposed to frost.
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Suitable applications and use in practice
A -40 °C dew point suits everywhere that condensation or moisture could damage equipment, disrupt production or endanger operational safety. In mechanical engineering and automation, dry air with a -40 °C dew point is used for pneumatic valves, cylinders and tools to prevent corrosion and the freezing of components in winter. Control and measurement technology (instrumentation) often requires exactly -40 °C as a guarantee that water will not condense in gauges, valves or sensors even at low ambient temperatures. In the chemical and petrochemical industries, -40 °C is the usual requirement for instrument air – air for actuating valves and control elements, especially where they are installed outdoors. Air this dry is also used in paint shops and powder coating, where moisture would cause surface defects. Similarly, in food production and pharmaceutical manufacturing, -40 °C ensures that no condensate supporting mould or bacterial growth arises in the air pipework or in contact with the product. In short, a -40 °C dew point is universally usable for most industrial operations that want certainty of dry air even at sub-zero temperatures.
Which types of dryer reach a -40 °C dew point
Adsorption dryers for compressed air are most often used to reach a -40 °C dew point. These dryers, equipped with a tower of hygroscopic material (sorbent), can remove moisture from the air down to the level at which condensation only occurs at -40 °C. Standard industrial adsorption dryers are designed for exactly -40 °C as the basic outlet dew point value. The advantage is that adsorption technology works reliably across a wide range of flows and pressures. Some adsorption dryer models optionally reach a milder dew point of -25 °C (saving energy) or, conversely, an extreme -70 °C (for the most demanding applications). Another type are membrane dryers, which use the selective permeability of membrane fibres to water vapour. Under certain conditions membrane dryers can also reach a pressure dew point of around -40 °C, but usually only at smaller flows and at the cost of consuming more of the air to purge the membrane. Refrigeration dryers (dryer type: refrigeration), by contrast, cannot deliver -40 °C – they work by cooling the air and commonly reach a dew point of only about +3 °C to +5 °C. For -40 °C, therefore, the adsorption or membrane technologies mentioned above must be used. In practice a combined solution is often chosen: a refrigeration dryer for pre-drying (lowering the dew point to a few °C above zero) followed by an adsorption dryer tuned to -40 °C. Such a combination minimises energy demand – the refrigeration dryer removes most of the water cheaply and the adsorption dryer then polishes the air to the required -40 °C.
Advantages and disadvantages of a -40 °C dew point
Advantages: The main advantage of -40 °C is that it represents reliable protection against condensation for most real conditions. If the principle applies that the pressure dew point should be at least 10 °C below the lowest ambient temperature, then -40 °C also covers situations where the surroundings drop to -30 °C. Air of this quality no longer causes pipe corrosion or frost damage to pneumatic systems. Compared with the extreme -70 °C, however, it is less energy-intensive – adsorption dryers for -40 °C consume less regeneration air (often around 5–15 % against up to 20 % for -70 °C) and some modern heat-regenerated types minimise losses further. Building and running such a dryer is also more economical; -40 °C units are widespread, available in various sizes and cost less than the „-70 °C“ variants. Another advantage is versatility – -40 °C satisfies most standards and requirements, so one dryer of this capability covers a wide spectrum of applications with no concern that the air might not be dry enough.
Disadvantages: Although -40 °C is far drier air than refrigeration dryers can achieve, it is still a more demanding technology than a +3 °C dew point, for instance. It requires adsorption or special membrane dryers, so both capital and running costs are higher than with the basic refrigeration option. Compressed air dried to -40 °C may have needlessly low humidity for some applications – for indoor pipework in air-conditioned halls where the temperature never falls below +10 °C, air this dry may be „an unnecessary luxury“. In such a case drying to a higher dew point such as -25 °C or even +3 °C would suffice, providing protection against condensation in milder conditions at lower cost. Another disadvantage is the energy consumption associated with reaching -40 °C – adsorption dryers have to regenerate the desiccant bed, which either takes away part of the compressed air (reducing system efficiency) or requires additional heating or a vacuum pump. That raises the overall energy demand of the compressor station. Nevertheless, compared with the extreme -70 °C, -40 °C is still a compromise between the required quality and cost. It is therefore used as the preferred choice where +3 °C is no longer enough but -70 °C is not necessary.
Links to other categories and information
If you are considering how dry your air needs to be, we recommend studying the neighbouring options alongside the -40 °C category: for milder requirements a pressure dew point of -25 °C or the standard values +3 °C or +5 °C may suffice (see our categories dew point +3 °C and dew point +5 °C). For extreme drying, on the other hand, we also offer dryers for a dew point of -70 °C. The various drying technologies are described in more detail in the overview of air dryer types – the difference between refrigeration and adsorption dryers, for example. The right choice of dew point and dryer type avoids needless cost and at the same time protects your system from the harmful effects of condensate.
More information about air drying and the dew point is in this article from our advice centre: Measuring the dew point temperature and Why and how to dry air
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RDP condensation dryers; pressure dew point +3 °C
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Condensation dryers WDF; dew point +3°C with filters
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HDI air dryers; pressure dew point +4°C
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RDL condensing dryers; pressure dew point +5°C
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ADRY air dryers; smaller adsorption -40°C
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BDRY air dryers; large adsorption -40°C
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MADRY air dryers; membrane -40°C
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Activated carbon columns; activated carbon separation
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Product sorting
List of products
The ADRY-150 Series Adsorption Dryer was designed for continuous separation of water vapor from compressed air at flow rates up to 2,500 l/min. Reduces the pressure dew point...
The ADRY-105 Series Adsorption Dryer was designed for continuous separation of water vapor from compressed air at flow rates up to 1,750 l/min. Reduces the pressure dew point...
The ADRY-12 series adsorption dryer has been designed for continuous separation of water vapour from compressed air at flow rates up to 200 l/min. Reduces the pressure dew point...
Adsorption dryer BDRY-600 designed for continuous separation of water vapour from compressed air with a flow rate of up to 7,708 l/min at a maximum pressure of 16 bar and...
The FDRY-1200 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 15,600 l/min at a maximum pressure of 16 bar...
Adsorption dryer BDRY-150 designed for permanent separation of water vapour from compressed air with a flow rate of up to 1 958 l/min at a maximum pressure of 16 bar and...
The BDRY-200 adsorption dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 2,617 l/min at a maximum pressure of 16 bar and...
The BDRY-250 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 3,400 l/min at a maximum pressure of 16 bar and...
Adsorption dryer BDRY-400 designed for permanent separation of water vapour from compressed air with a flow rate of up to 5 358 l/min at a maximum pressure of 16 bar and...
Adsorption dryer BDRY-110 designed for permanent separation of water vapour from compressed air with a flow rate of up to 1 433 l/min at a maximum pressure of 16 bar and...
The BDRY-1000 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 13,067 l/min at a maximum pressure of 16 bar...
The FDRY-5000 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 65,000 l/min at a maximum pressure of 16 bar...
The FDRY-2000 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 26,000 l/min at a maximum pressure of 16 bar...
The ADRY-60 series adsorption dryer was designed for continuous separation of water vapour from compressed air at flow rates up to 1,000 l/min. Reduces the pressure dew point...
Adsorption dryer BDRY-300 designed for permanent separation of water vapour from compressed air with a flow rate of up to 4,183 l/min at a maximum pressure of 16 bar and...
The ADRY-6 series adsorption dryer has been designed for continuous separation of water vapour from compressed air at flow rates up to 100 l/min. Reduces the pressure dew point...
The ADRY-200 Series Adsorption Dryer was designed for continuous separation of water vapor from compressed air at flow rates up to 3,333 l/min. Reduces the pressure dew point...
The ADRY-24 series adsorption dryer was designed for continuous separation of water vapour from compressed air at flow rates up to 400 l/min. Reduces the pressure dew point down...
The ADRY-36 series adsorption dryer has been designed for continuous separation of water vapour from compressed air at flow rates up to 600 l/min. Reduces the pressure dew point...
The ADRY-75 Series Adsorption Dryer was designed for continuous separation of water vapor from compressed air at flow rates up to 1,250 l/min. Reduces the pressure dew point...
Adsorption dryer BDRY-1200 designed for continuous separation of water vapour from compressed air with a flow rate of up to 15,050 l/min at a maximum pressure of 16 bar and...
Adsorption dryer BDRY-800 designed for permanent separation of water vapour from compressed air with a flow rate of up to 10 058 l/min at a maximum pressure of 16 bar and...
The FDRY-1500 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 19,500 l/min at a maximum pressure of 16 bar...
The FDRY-2500 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 32,500 l/min at a maximum pressure of 16 bar...
The FDRY-3000 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 39,000 l/min at a maximum pressure of 16 bar...
The FDRY-3750 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 48,750 l/min at a maximum pressure of 16 bar...
The FDRY-6500 Adsorption Dryer is designed for continuous separation of water vapour from compressed air with a flow rate of up to 84,500 l/min at a maximum pressure of 16 bar...
MADRY-12 membrane dryer with compressed air flow up to 12 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-123 membrane dryer with compressed air flow up to 123 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to...
MADRY-18 membrane dryer with compressed air flow up to 18 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-180 membrane dryer with compressed air flow up to 180 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to...
MADRY-24 membrane dryer with compressed air flow up to 24 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-3 membrane dryer with compressed air flow up to 3 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-32 membrane dryer with compressed air flow up to 32 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-44 membrane dryer with compressed air flow up to 48 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-6 membrane dryer with compressed air flow up to 6 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-63 membrane dryer with compressed air flow up to 63 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-9 membrane dryer with compressed air flow up to 9 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...
MADRY-90 membrane dryer with compressed air flow up to 90 m³/hr up to 12 bar. Including 2 filters through the dryer and filter cartridge clogging indication. Designed to supply...