How to Choose the Right Hankison Membrane Dryer

Choosing the right membrane dryer depends on more than just how much compressed air you use. Air flow, operating pressure, inlet temperature, required dew point and air quality all play a role in determining which Hankison HMD or HMM model is suitable for the installation.

In this guide, we go through the most important information you should have ready before selecting a membrane dryer.
If you would first like to learn about the different Hankison HMD and HMM series, you can read our guide to Hankison HMD and HMM membrane dryers.

1. How Much Compressed Air Needs to Be Dried?

The first thing you need to know is your air consumption.
Air consumption is typically specified in m³/h, and it is important to know the actual consumption at the relevant operating point.

The Hankison HMD series covers approximately 2.6–112.8 m³/h, while the HMM series ranges from approximately 2.4–240 m³/h.
However, this does not mean that you should simply choose the model with a catalogue capacity just above your air consumption.
The dryer’s performance must be evaluated in relation to the actual operating conditions.

Pay particular attention to:

  • Normal air consumption
  • Maximum air consumption
  • Any peak loads
  • Constant or varying air consumption
  • Future changes in air consumption

If air consumption varies significantly, the sizing should take into account how the compressed air system actually operates.

2. What Is Your Operating Pressure?

Operating pressure is an important part of the sizing process.
A membrane dryer must be selected based on the pressure available at the dryer’s inlet.

It is therefore a good idea to specify:

Inlet pressure: ______ bar

If the pressure varies, both the minimum and normal operating pressure should be specified.

3. What Is the Temperature of the Compressed Air?

The temperature of the compressed air at the dryer’s inlet affects the sizing.
You should therefore know the approximate inlet temperature rather than relying solely on the compressor’s nominal operating temperature.
This is particularly relevant if the dryer is installed close to the compressor, downstream of an aftercooler, or in a warm production environment.

Inlet temperature: ______ °C

4. How Low Does the Dew Point Need to Be?

The dew point is one of the most important factors when selecting a membrane dryer.
The lower the temperature to which the compressed air may be exposed without condensation or freezing, the lower the required pressure dew point must be.

Hankison membrane dryers can be configured for different dew point levels depending on the model and operating conditions.
The manufacturer’s documentation includes solutions down to approximately -40 °C.

This means you should start by asking:

How cold will the dried air installation become?

If, for example, the air is routed outdoors after the dryer or passes through a cold area, this must be taken into account when selecting the dryer.

5. Where Will the Dryer Be Installed?

The installation location can affect which solution is most practical.

Point-of-use installation:

If only one machine or process requires dry air, a membrane dryer can be installed close to the point of use.
This is a typical point-of-use solution.

Central installation:

If several consumers need to be supplied with dry air, a more central solution may be relevant.
In this case, the pipework downstream of the dryer must also be taken into account. If the dried air passes through a cold area, the dew point must still be sufficiently low.

6. HMD or HMM?

Once the basic operating data is known, you can start looking at the appropriate series.

Choose HMD when:

  • You have a local point of use
  • The dryer needs to be integrated into existing equipment
  • You have a small or medium air flow
  • A compact solution is required
  • Dry air needs to be produced close to the point of use

The HMD series covers approximately 2.6–112.8 m³/h.

Choose HMM when:

  • There is a continuous air flow
  • The air flow is higher
  • A modular solution is preferred
  • The dryer is part of an industrial or process-oriented installation

The HMM series covers approximately 2.4–240 m³/h.

However, the final selection should always be based on the actual operating data.

See the current Hankison membrane dryers and the individual HMD and HMM models.

7. Remember Filtration

A membrane dryer must be protected against contamination from the compressed air system.

Appropriate filtration should therefore be installed upstream of the dryer to protect against, among other things:

  • Oil
  • Water
  • Dust
  • Rust
  • Particles from the pipe installation

Hankison specifically states that particle and oil separation is required to protect the membrane.
If you are unsure about the filter combination, it should be sized at the same time as the dryer.

Example: How to Start Sizing the Dryer

Imagine that a machine uses:

25 m³/h at 7 bar

and that dry compressed air is required because the installation is located outdoors.

You already have three important pieces of information:

  • Air flow: 25 m³/h
  • Operating pressure: 7 bar
  • Installation: Outdoor

The next question is:

How low does the pressure dew point need to be?

If the installation may be exposed to freezing temperatures, the dew point must be selected so that condensation and freezing are avoided at the relevant temperature.
Only once this information is known does it make sense to select the specific HMD or HMM model.

Checklist Before You Choose

Before ordering a Hankison membrane dryer, you should have at least the following information available:

☐ Air consumption in m³/h

☐ Minimum and normal operating pressure

☐ Inlet temperature

☐ Required pressure dew point

☐ Oil content/compressor type

☐ Filtration requirements

☐ Dryer installation location

☐ Whether air consumption is constant or variable

☐ Whether the installation is indoors or outdoors

☐ Any specific air quality requirements

With this information available, it is much easier to find the right model and avoid selecting a dryer that is either undersized or unnecessarily large.

Do Not Size the Dryer Based on Air Flow Alone

One of the most common mistakes when selecting a compressed air dryer is to look only at the m³/h rating.
A model that can handle the required air flow on paper is not necessarily the right solution.

This is because capacity must be considered in relation to factors such as:

  • Inlet pressure
  • Inlet temperature
  • Required dew point
  • Air quality
  • Operating time
  • Air consumption

The final model should therefore be selected based on the manufacturer’s sizing data and the actual operating point.

What If You Do Not Know Your Required Dew Point?

If you do not know which dew point you need, you should start with the actual application.

Ask yourself questions such as:

  1. How cold can the installation become?
  2. Is there a risk of freezing?
  3. Are there already problems with condensation?
  4. Does the compressed air come into direct contact with a product or process?
  5. Is the compressed air being used to protect instruments or pneumatic components?

The more critical the application, the more important it is to define the specific pressure dew point requirement.

Should You Choose HMD or HMM?

If you have a small, local installation, the HMD series is often the natural place to start.
If you have a continuous air flow and a higher air demand, the HMM series should be considered.
However, there is no single model that is right for every installation.
The right solution is determined by the combination of air flow, pressure, temperature, dew point and filtration.

If you are unsure, you can use this short sequence as a starting point:

Air flow → pressure → temperature → dew point → filtration → HMD/HMM → specific model

Do You Need Help Sizing the Dryer?

If you need help selecting the right Hankison membrane dryer, it is useful to have the following information ready:

Air consumption: ______ m³/h

Operating pressure: ______ bar

Inlet temperature: ______ °C

Required dew point: ______ °C

Compressor type: ______

Application: ______

Indoor/outdoor: ______

Once you have this information ready, you can send it to us, so we can help assess the relevant HMD or HMM model and the required filtration.