Understand the importance of proper air preparation

Pneumatic products, systems and machines require clean compressed air to operate efficiently and reliably.

Particles, water and oil in compressed air will shorten the service life and function of components and systems. They also undermine productivity and energy efficiency. Knowing how to achieve proper compressed air quality and the filters needed to achieve the recommended air quality required for common industrial applications is essential for a well-functioning plant.

Air Preparation Air Preparation

There are three variables:Compressed air purity, compressed air volume (flow) and air pressure. According to the system requirements, the coordination of these three variables can ensure a high compressed air quality and form the basis for selecting suitable maintenance unit components.

The required compressed air purity improves the operating performance and efficiency of pneumatic systems and ensures compliance with legal regulations in industries such as food and beverage. The flow rate is mainly determined by the flow cross section and the design size of the machine.

Generally, if the design is the same, the larger assembly will have a higher flow rate. Optimized working pressure increases efficiency, minimizes wear and reduces power consumption. In order to coordinate the compressed air purity, compressed air volume and pressure of the system specifications, the correct individual components must be selected. These components include on-off valves, booster valves, pressure regulators, water separators, filters and drying units.

Why do we need to filter?

The atmosphere contains dust and dirt particles, not to mention a lot of moisture in the form of moisture. The air produced by the compressor will be hot, humid and dirty. Thus, the first step is to filter out these contaminants starting with the removal of moisture. This is usually achieved by a freeze dryer next to the compressor, which simply cools the air to just above the freezing point (〜3 ˚C) and remove the condensed liquid.

Failure-free operation of system components, such as valves and cylinders, cannot be guaranteed in the long term if contaminants are not filtered out. Inadequate preparation of compressed air can cause expansion and premature wear of the sealing ring, and contaminate the control valve. Therefore, correct compressed air preparation is essential to reduce machine downtime and idle time, as well as reduce maintenance and energy costs.

To help everyone communicate in the same language about air quality,International standards were established in 2010ISO 8573, which contains the definition of compressed air quality. Air quality is defined by the rating of three pollutants: solid particles, condensed water content and oil content. The rating range is1-9The smaller the number, the higher the air purity. It specifies the maximum allowable contamination level and particle size for the corresponding quality class. The air quality rating will help you determine which type of filter or filter combination you need.

Best Practices-Filtration for common applications

Here are some common applications with corresponding air quality ratings and filtration types.

Standard automation components such as valves and cylinders
Quality grade7.4.4–40 µmFilter
Proportional Valves, Compact Valves, Pneumatic Tools
Quality grade6.4.4–5 µmFilter
Main packaging, reduce odor and oil vapor
Quality grade1.4. 1-5,and0.01 µm, and activated carbon filter
Semiconductor Industry, Pharmaceutical Products
Quality grade1.3.1-5,1and0.01 µm, and activated carbon, membrane dryer

The required air quality rating or filtration level is usually defined by standard industry guidelines or best practices. Most air treatment equipment manufacturers can provide reference documents that define air quality requirements for different applications and industries. After determining the ideal air purity level to apply, select the most suitable filter and dryer. Guidelines for filters and dryers are provided below.

Types of filters and when to use them

There are many types of filter assemblies used to remove contaminants such as solid particles, liquid water and water vapor, oil vapor, odorants, and even bacteria and viruses. For most automation applications, the focus is on the removal of solid particles and water.

The water separator uses a centrifugal design or a coalescence principle to remove condensed water.

The centrifugal separator induces a rotational motion in the air, forcing the particles to accelerate in a radially outward motion. Once outside, they drain into a bowl. The centrifugal separator can effectively remove more5Micron droplets and dust. This process requires no maintenance.

The coalescing separator causes air to flow from the inside to the outside of the filter element. These filter cartridges must be replaced periodically.

Filters are used to remove particles, condensate and oil.

The pore size of the coarse particle filter is5To40 µm. The air flows through the centrifugal separator and then through the filter element. The filter element is typically a sintered material, such as polyethylene or bronze.

Fine filters and microfilters remove less1 µm,0.01 µmof particles. Air flows from the inside to the outside of the filter element. The solid particles got stuck in the filter element and blocked the filter element. Fluid particles such as condensate or oil will coalesce or attach to larger droplets, which will float and be trapped in the filter bowl. It is important to cascade the filters to avoid premature clogging of the filter elements. For example, if you need1 µmfiltering, we recommend using5 µmFilter, that1 µmThe filter will not be clogged with large particles.

The activated carbon filter combines hydrocarbon residues, odorants and oil vapors. They are used in applications such as food packaging and treating odors in pharmaceuticals.

A sterile filter ensures that the air is free of bacteria.

The dryer is used to remove water vapor, which exceeds the capacity of fine and micro-coalescing filters, and is classified according to the available pressure dew point. The pressure dew point defines the temperature to which the compressed air can be cooled without condensing water. If the temperature is lower than the pressure dew point, condensed water will form. Even if the temperature is subsequently increased, this condensed water will remain and may lead to corrosion of the components.

Refrigeration dryers are typically located downstream of the plant air compressor. The air is cooled in the cooling device to just freeze, and the discharged condensed water is discharged. The pressure dew point reached is approximately3°C. To avoid condensation, it is recommended that the pressure dew point must be lower than the ambient temperature10°C. For working temperature never below13°CFor the system, a freeze dryer is sufficient.

Membrane dryers can reduce the pressure dew point, such as reducing20°C. The air flows longitudinally through a bundle of parallel hollow fibers. During this process, water vapor diffuses due to the local pressure drop from the inside of the fiber to the outside. Purge air was used to vent the vapors. Due to the use of purge air, the maintenance-free membrane dryer has a certain amount of constant exhaust/Air consumption.

When the required pressure dew point is-40 °To-70 °CPlease use the adsorption dryer. Dryers utilize molecular forces to bind gas or vapor molecules to a desiccant, such as desiccant beads. Since the desiccant is renewable, two chambers are required: when one is dry, the other has time for cold or hot regeneration. In equipment with cold regeneration, some dry air is used to dry the binder. When using thermal regeneration, water evaporates when heated. The desiccant must be replaced regularly, for example, in service8,000Hours later.