How Does An Air Preparation Unit Work?

Post By: Tom Rowse On: 06-03-2023 Read Time: 5 minutes - Guides - Pneumatics

In any pneumatic system, you need to control your equipment centrally and maintain the compressed air quality. This means that you’ll need a reliable and pure air supply, to ensure that all the various components achieve their optimal life expectancy. With proper air preparation, you’ll optimise your machinery’s availability, enhance its reliability, accuracy & safety, and ensure the most efficient energy consumption.

How Does An Air Preparation Unit Work?

Air preparation units generally consist of a range of components, including:

  • Filters, with optional fine, high-flow and activated carbon filters
  • Regulators, including pressure regulators
  • Dryers
  • Sensors, for pressure and flow measurement
  • Valves, including pressure regulation, safety and on/off valves

Filters

Filtration is critical in maintaining compressed air quality, with various components involved in the air treatment process. The filters themselves clean the compressed air of particulates and moisture. The air is then regulated, and if necessary, dried with an additional dryer to further reduce the moisture content.

Filter Regulator Unit

The filter regulator unit is the first step in air preparation. It regulates the compressed air pressure, by means of a condensate bowl with a filter in its housing. This unit removes moisture from the compressed air, using a vortex to create centrifugal force. There’s a manual or automatic drain in the base of the bowl where the collected moisture is drained off. The compressed air then passes through a filter, which traps the solid particles such as dust or dirt.

Fine filter

Standard filtration levels are typically 40 µm and 5 µm, but the level of filtration can be adjusted to meet your requirements. If you need higher-quality compressed air filtration, you need to use a finer filter, such as 1 µm. Filtration to this level should be conducted in several stages, first capturing the larger particles in a lower-grade filter so they don’t clog up the finer filter and create a pressure drop. You can monitor the filter saturation using a differential pressure indicator.

Air Preparation Unit

Filter Regulator Unit

The filter regulator unit is the first step in air preparation. It regulates the compressed air pressure, by means of a condensate bowl with a filter in its housing. This unit removes moisture from the compressed air, using a vortex to create centrifugal force. There’s a manual or automatic drain in the base of the bowl where the collected moisture is drained off. The compressed air then passes through a filter, which traps the solid particles such as dust or dirt.

Fine filter

Standard filtration levels are typically 40 µm and 5 µm, but the level of filtration can be adjusted to meet your requirements. If you need higher-quality compressed air filtration, you need to use a finer filter, such as 1 µm. Filtration to this level should be conducted in several stages, first capturing the larger particles in a lower-grade filter so they don’t clog up the finer filter and create a pressure drop. You can monitor the filter saturation using a differential pressure indicator.

High Flow Filter

Filters inevitably increase the compressed airflow’s resistance and consequently reduce the overall flow rate. You can reduce the impact on your airflow with High Flow filters, which have a larger surface area but take up more installation space.

Activated Carbon Filter

Activated carbon filters are high-quality filters used specifically to filter out oil and aerosols. The activated carbon molecules attract these particulates and remove them from their air, providing purity down to a level of 0.003 mg/m3.

Membrane Dryer

Membrane dryers are used for additional deep air drying, when all other filters are unable to reduce the moisture content enough for your purpose. Standard filtration reduces the pressure dew point to 3°C, with the result that compressed air above 3°C is unable to condense and causes moisture to collect in the pipe.

Some critical applications demand a lower dew point, which you can do with a membrane dryer. A moisture-absorbing membrane separates two chambers in the dryer. These have a small pressure difference which forces the compressed air through the membrane, which then absorbs the moisture as the air passes through. You can reduce the pressure dew point of compressed air by at least 15°C in this way.

How Does An Air Preperation

Sensors

To control your pneumatic system centrally, you can install various sensors in the air supply system to monitor different parameters. The most important of these are pressure and flow (also known as volume flow or throughput).

Pressure Sensors

You can install pressure sensors on almost any air supply equipment, as they don’t need airflow to make a measurement. You can choose basic teach-in sensors with LED displays, that show adjustable pressure levels. Alternatively, you might go for more complex programmable options, with multi-coloured readable LCDs.

Flow Sensors

Flow sensors are only available as a separate module, because they must be installed in the flow direction. To measure reliably, they must also be placed in a laminar airflow. You can do this by installing the flow sensors behind another component, which won’t cause any eddies or disturbances. You can only assemble the sensor in this way if you put a non-specific function manifold block on the incoming side.

Valves

To control your particular application centrally, you’ll need to install several valves in your air preparation system.

Pressure regulator valve

The pressure regulator is one of the most important valves in an air preparation unit. With this, you can regulate the working pressure simply by turning a knob. This causes the main spring in the valve to adjust the force on the diaphragm. A regulating piston in the valve travels downwards with the diaphragm, where it releases a lower sealing seat. Secondary venting allows the air to escape if the set working pressure is exceeded by the pressure at the working port. You can monitor and, if necessary, adjust the pressure, using a pressure gauge or sensor.

Safety Valve

Safety valves are necessary to guarantee the safety of people, equipment and the environment. Safety valves combine several functions:

  • Rapidly depressurising the system using a quick exhaust or dump valve
  • Bringing the system gradually up to pressure with a slow start valve
  • Installing duplicate coils and position sensors to create redundant valves, in case of possible product failures

Switch-On/shut-Off valve

You can use a manually operated, central on/off valve to shut off the main pressure, which simultaneously vents the pressure on the work side. A Lock-Out/Tag-Out (LOTO) switch is fitted in the switch’s rotary knob to provide safe machine maintenance. You can also get electrical switching valves that you can control, for example, with a PLC.

Preparation, safety and sustainability

Proper air preparation will greatly enhance the life expectancy and performance of your pneumatic equipment and systems. With various configurations and optional additional units, you can fine-tune your air supply to a greater or lesser degree of purity and pressure. You’ll also make it safer to use, and reduce your energy consumption, thus creating overall benefits for the environment.