Sušičky vzduchu tlakový rosný bod -70 °C

What a -70 °C dew point means and why it matters

A pressure dew point of -70 °C is the temperature at which water vapour starts to condense in compressed air while the air is at working pressure. In other words, this is extremely dry air – only a negligible amount of moisture remains in the air pipework. Such a low dew point matters wherever any trace of water in the air is undesirable. It guarantees customers that even at very low ambient temperatures (well below freezing) no condensation or icing of moisture will occur in the system. That protects equipment against corrosion, blockage or frost damage and ensures the highest air quality for sensitive applications.

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Suitable applications and use in practice

A -70 °C dew point is used in the most demanding branches of industry and technology. Typical examples are laboratories, pharmaceuticals, electronics and the food industry, where even minimal moisture can spoil products or processes. In the electronics and optics industries, ultra-dry air prevents condensate forming on sensitive components. In pharmaceuticals and food production it helps maintain strict hygiene conditions and prevents the growth of micro-organisms caused by moisture. A -70 °C dew point is also essential for outdoor installations in cold climates – in the gas or petrochemical industries, for instance, where outdoor temperatures fall well below zero. In such conditions the air must be dried to -70 °C so that condensate does not freeze in pipes and instruments. This extremely dry air also corresponds to class 1 to ISO 8573-1 (the highest purity in terms of water content).

Types of dryer that reach a -70 °C dew point

A pressure dew point of -70 °C can be reached practically only by adsorption dryers. These are dryers filled with a highly porous sorbent (typically a desiccant such as silica gel or activated alumina) that retains water molecules. Adsorption dryers are usually twin-tower systems with bed regeneration – while one tower dries the air, the other regenerates (is dehumidified) using a small stream of already dried air or external heating. Good industrial adsorption dryers easily reach a dew point of -40 °C as standard and, in a special design, exactly this -70 °C. By contrast, neither refrigeration dryers (dryer type: refrigeration) nor membrane dryers (dryer type: membrane) reach such low values – a refrigeration dryer works by cooling the air and only gets down to +3 °C at the limit, while a membrane dryer commonly manages around -40 °C at a small flow. To reach a -70 °C dew point a combination of technologies is often chosen: the air is first dried by a refrigeration dryer to about +3 °C (most of the moisture is removed) and then polished by an adsorption dryer to -70 °C. That saves on the adsorption dryer's running costs, because it is already handling considerably drier air.

Advantages and disadvantages of a -70 °C dew point

Advantages: The main advantage of a -70 °C dew point is maximum protection of the system against water. Even at extremely low ambient temperatures (freezing winter nights or cold-store operations, for example) there is no risk of condensation or moisture freezing in the pipework. That extends equipment life, eliminates corrosion in the distribution system and increases the reliability of pneumatic components. Ultra-dry air is additionally essential to achieve the highest quality under air purity standards – with -70 °C you meet even the strictest requirements (ISO 8573-1 class 1 for water). Another advantage is that air without moisture causes no problems in sensitive production processes (it does not disturb chemical reactions through the presence of water, and causes no coating or electronics defects).

Disadvantages: The lowest dew point also brings increased costs and maintenance demands. To reach -70 °C, adsorption dryers need a significant part of the compressed air for regeneration (up to around 15–20 % of the flow on heatless types) or higher energy consumption (on dryers with external heating or vacuum regeneration). That raises the running costs of the compressor station. The bed (sorbent) in the adsorption towers must also be changed regularly, because it wears out. The capital cost of a dryer capable of -70 °C is higher than that of ordinary dryers with a -40 °C or +3 °C dew point. Not least, if such extreme drying is not essential for the given application, it may be a needlessly oversized solution – air that is drier than required only means higher outlay. It is therefore worth considering carefully whether a dew point as low as -70 °C is really necessary, or whether the more common -40 °C dew point or the intermediate -25 °C value would suffice. For many industrial operations a -40 °C dew point is enough to protect against condensate, while -70 °C is used only in specific cases with extreme requirements.

Links to related information

Our website offers further useful information on air drying too. If you are considering which dew point to choose, read the article about the -40 °C dew point category, a frequent industrial standard, or about the milder -25 °C dew point category. You can also look at the overview of the various types of air dryer – the differences between refrigeration and adsorption dryers, for instance – so that you choose the optimal technology for the dew point you need. The right choice of dew point and dryer type will give you efficient operation of the compressor station and a reliable supply of quality compressed air.

All compressed air dryers and more information about air drying and the dew point can be found in this article from our advice centre: Measuring the dew point temperature and Why and how to dry air

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Adsorption air dryer ADRY-150

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€5 216,32 excl. VAT

€6 311,75 / pcs

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...

Code: ADRY-150

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FREE €4 592,24 –3 %

Adsorption air dryer ADRY-105

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€3 681,38 excl. VAT

€4 454,47 / pcs

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...

Code: ADRY-105

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FREE €2 243,77 –3 %

Adsorption air dryer ADRY-12

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€1 798,72 excl. VAT

€2 176,45 / pcs

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...

Code: ADRY-12

Sušičky vzduchu tlakový rosný bod -70 °C

What a -70 °C dew point means and why it matters

Suitable applications and use in practice

Types of dryer that reach a -70 °C dew point

Advantages and disadvantages of a -70 °C dew point

Links to related information

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