Membrane Dryer – What Is It and How Does It Work?

A membrane dryer for compressed air is used to remove moisture and water vapour from compressed air.
It is an efficient and compact solution when you need dry compressed air for applications such as pneumatic tools, instrumentation, automation or other installations where moisture can cause problems.
But what exactly is a membrane dryer, how does it work, and when should you choose a membrane dryer over another type of compressed air dryer?

In this guide, you will find answers to the most important questions.

What Is a Membrane Dryer?

A membrane dryer is a type of compressed air dryer that removes water vapour from compressed air using a special membrane.
Inside the membrane dryer are a large number of very fine hollow membrane fibres. The membrane is made from a material that allows water vapour to pass through it, while most of the other components of the air remain in the compressed air stream.
This means that the air supplied to your equipment is significantly drier.
A membrane dryer has no refrigeration circuit and does not use a conventional desiccant. This makes the design simple, compact and reliable.

In short: Moist compressed air → membrane → water vapour removed → dry compressed air

How Does a Membrane Dryer Work?

When air is compressed in a compressor, it still contains water vapour.
When the hot compressed air subsequently cools down, the water vapour can condense into liquid water.
This can cause problems in the compressed air system.
A membrane dryer reduces this moisture using membrane fibres.

1. Moist Compressed Air Enters the Membrane Dryer

The compressed air is fed into the membrane dryer.
The air may contain both water vapour and other contaminants, which is why the compressed air should be properly filtered before entering the membrane dryer.

2. The Compressed Air Passes Through the Membrane Fibres

Inside the drying unit, the compressed air passes through the many hollow membrane fibres.
The membrane is selective. Water vapour can pass through the membrane material much more easily than the other components of the air.

3. The Water Vapour Is Removed

A small portion of the dried air is used as so-called purge air.
The purge air helps carry the water vapour that has passed through the membrane away from the drying unit.

4. Dry Air Is Supplied to the System

The remaining air leaves the membrane dryer as dried compressed air and can then be used in the pneumatic system.
This process enables the membrane dryer to reduce the moisture content of the compressed air.

Why Is Dry Compressed Air Important?

Moisture in compressed air can lead to a number of problems.

When water condenses in a compressed air system, it can, among other things, cause:

• Corrosion and rust in pipes and components
• Problems with pneumatic valves
• Wear on pneumatic equipment
• Condensation in compressed air hoses
• Operational problems in automated systems
• Reduced quality in spray painting
• Risk of freezing in outdoor installations
• Problems with sensitive measuring and instrumentation equipment

By removing water vapour, a compressed air dryer can therefore help protect both the installation and the equipment using the compressed air.

What Is Pressure Dew Point?

When choosing a membrane dryer, the pressure dew point is an important specification.
The dew point indicates the temperature at which water vapour in the air begins to condense.
The lower the dew point, the lower the temperature the compressed air can be exposed to without condensation forming.
This is particularly important in installations where the compressed air is exposed to low temperatures.
For example, an installation in an unheated hall or outdoors is more exposed to condensation and freezing than an installation in a heated production facility.
When choosing a membrane dryer, you should therefore always consider the required dew point for your specific installation.

Advantages of a Membrane Dryer

A membrane dryer offers several advantages compared with other types of compressed air dryers.

Compact Size

Membrane dryers typically have a compact design and can therefore be installed where space is limited.
This makes them suitable for smaller installations and for drying compressed air close to the point of use.

No Electricity Required

A membrane dryer can operate without a separate electrical power supply for the drying process itself.
The drying process takes place using the compressed air and the properties of the membrane.

No Moving Parts

Membrane dryers have no compressor or refrigeration circuit and therefore have a simple design with few mechanical components.
This can be an advantage when you want a reliable solution with limited maintenance requirements.

Low Maintenance Requirements

A membrane dryer normally requires limited maintenance.
However, it is important that the compressed air is properly filtered so that oil, particles and other contaminants do not damage or overload the membrane.

Suitable for Point-of-Use Drying

One of the major advantages of a membrane dryer is the ability to dry compressed air exactly where it is needed.
You therefore do not necessarily need to dry the entire compressed air supply if only individual machines or points of use require very dry air.

What Is a Membrane Dryer Used For?

Membrane dryers are used in many different types of compressed air installations.

Typical applications include:

Pneumatics – Dry compressed air can be important for pneumatic valves, cylinders and automation systems, where condensation and moisture can cause operational problems.

Instrument Air – Measuring and control equipment may require dry and clean compressed air to operate reliably.

Spray Painting – Moisture in compressed air can affect the results of coating and painting applications. A compressed air dryer can help reduce the risk of moisture-related problems.

Outdoor Installations – In outdoor compressed air installations, low temperatures can increase the risk of condensation and freezing. A lower dew point can be particularly relevant in these applications.

Sensitive Equipment – Certain instruments, production machines and pneumatic components require a drier air quality than a standard compressed air system can provide on its own.

Membrane Dryer vs. Refrigerated Dryer

There are several different technologies available for drying compressed air.

A refrigerated dryer cools the compressed air so that the water vapour condenses and can be removed.
Refrigerated dryers are commonly used in standard industrial compressed air systems and for larger air volumes.

A membrane dryer, on the other hand, removes water vapour through a membrane and is particularly suitable for smaller air volumes, point-of-use drying and installations where a compact solution is an advantage.

The choice depends on factors including:

• Air consumption
• Operating pressure
• Inlet temperature
• Required dew point
• Air quality requirements
• Installation conditions
• Energy consumption
• How much of the compressed air needs to be dried

There is therefore no single type of compressed air dryer that is suitable for every installation.

What Is Purge Air?

Purge air is a small portion of the dried compressed air used to carry moisture away from the membrane.
It is an important part of how a membrane dryer operates.
When choosing a membrane dryer, you should therefore not only consider the inlet air flow rate. You should also check the purge air consumption.
A higher drying requirement and a lower dew point can in some cases result in a higher purge air requirement.
This means that correct sizing is important to achieve the desired air quality without unnecessarily high compressed air consumption.

Remember to Filter the Air Before the Membrane Dryer

To ensure stable operation and a long service life, the membrane dryer should be supplied with properly filtered compressed air.
Oil, aerosols, water droplets and particles can affect the membrane and reduce the dryer’s efficiency.

A typical installation may therefore consist of:

Compressor → aftercooler/water separator → compressed air filter → membrane dryer → dry compressed air → point of use

The exact configuration depends on the compressor, air quality and requirements of the specific installation.

How Do You Choose the Right Membrane Dryer?

When purchasing a membrane dryer, it is important to choose a model that matches your compressed air system.

We particularly recommend considering the following:

1. Air Consumption

How much compressed air needs to be dried?

Air consumption may, for example, be specified in l/min or m³/h.

2. Operating Pressure

At what pressure does your compressed air system operate?

The membrane dryer must be sized for the system’s actual operating pressure.

3. Required Dew Point

How dry does the compressed air need to be?

This is particularly important if the compressed air will be used outdoors or in cold environments.

4. Inlet Temperature

The temperature of the compressed air at the membrane dryer affects the drying process and the overall performance.

5. Purge Air Consumption

Check how much compressed air the membrane dryer uses for purging.

6. Air Quality

Check the filtration requirements before the membrane dryer, especially if the compressed air contains oil or a high concentration of particles.

Frequently Asked Questions About Membrane Dryers

What Does a Membrane Dryer Do?

A membrane dryer removes water vapour from compressed air using a semi-permeable membrane. The result is drier compressed air with a lower dew point.

Does a Membrane Dryer Use Electricity?

The membrane drying process itself normally does not require a separate electrical power supply. The drying process uses compressed air and purge air.

Does a Membrane Dryer Use Refrigerant?

No. A membrane dryer operates without a refrigeration circuit or refrigerant.

Does a Membrane Dryer Need a Filter?

Yes. Proper filtration of the compressed air is important to protect the membrane from oil, particles and other contaminants.

Where Are Membrane Dryers Used?

They are used for applications including pneumatics, instrument air, spray painting, automation, sensitive equipment and installations where there is a risk of condensation or freezing.

What Is the Difference Between a Membrane Dryer and a Refrigerated Dryer?

A membrane dryer removes water vapour through a membrane, whereas a refrigerated dryer cools the compressed air to make the water vapour condense. Membrane dryers are particularly suitable for compact installations and point-of-use drying.

Find the Right Membrane Dryer for Your Compressed Air System

If you need dry compressed air, a membrane dryer can be a simple and compact solution.

The most important thing is to choose a model based on the actual air consumption, operating pressure, required dew point and air quality requirements.

You can view our membrane dryers for compressed air and find a model that suits your compressed air system.

If you are unsure which membrane dryer to choose, you should base your selection on the specifications of your existing compressed air system and the equipment that needs to be supplied with dry air.

If you are unsure about sizing or model selection, you are welcome to contact us about choosing a membrane dryer. We can help assess which solution is suitable for your compressed air system.

In short: A membrane dryer is an effective way to reduce moisture in compressed air without refrigerant and without a complex refrigeration circuit. Its compact design makes the technology particularly suitable when you need dry compressed air at a specific point of use.