Air Blow Off

All the compressed air enhancement nozzles used for air blow off systems work under the same basic operating principles. Compressed air enters the nozzle and is shaped into an outlet pattern of increased velocity air flow. Additional air inlet holes allow the surrounding air to be drawn into the nozzle and/or the external shape of the nozzle encourages further air entrainment by the Coanda effect. The result is a significant amplification of the amount of air moved.

Whilst the various types of air nozzles do operate under the same principles they produce very different effects in terms of blow off area and force. Understanding these differences is important when working out which is the best product for a specific situation

Air Knives (long line pattern with high impact) – Will produce high impact air force concentrated in a line along the length of the knife. As the pattern is linear if a surface needs to be treated the some sort of relative motion needs to be introduced. The most common method for this is to deploy the air knives on a conveyor so the product passes through the line of air.

Air Edgers (short line pattern very high impact) – These produce a very high impact air force over a short length. They operate like short by highly focused versions of air knives.

Air Jets – (circular pattern with medium impact) – These nozzles produce a focused relatively high impact jet. Looking face onto the nozzle it would produce a circular air current. The air jet sits somewhere between the very focused air nozzle and the less focused air amplifier. It is a good choice of product for spot blow off systems that require a reasonable amount of impact.

Air Nozzles – (narrow circular pattern with high impact)- These nozzle are shaped to produce a single jet or stream of air. They are engineered to ensure the resulting air flow remains laminar as long as possible. They are best deployed when precise high impact jets are needed to hit a spot or point for blow-off.

Ring blade – These are essentially air knives that have been bent around to form a circle. The air force is directed inwards and so are used on extrusions and other tubular shaped product lines when can pass through the ring blade. They produce high impact lines of air but the line is bent round into a circle.

When compared to blower systems enhanced compressed are blow off systems are very easy to maintain. Whether the system is comprised of air nozzles, air knives, air jets or air edgers there are no moving parts involved and no external power is required. This means that there is virtually nothing to go wrong with the blow off system.

The simplicity of these systems means they can be deployed in areas that would preclude the deployment of powered blowers. In dirty, wet or humid areas of the production facility any powered equipment requires often costly protection to prevent it breaking down. This may involve water proofing or additional filtration / dust protection. Compressed air systems

Noise is a constant hazard when using air systems. Both blowers and compressed air blow off systems can be very noisy and constant exposure to high noise levels is a big health and safety concern. Indeed, there is stringent legislation in many countries that limit workers exposure to certain noise levels in the work place. As such noise reduction is often a critical design factor in air blow off applications.

A raw open air line may produce dangerous levels of noise perhaps 98 Db or more. All the compressed air enhancement nozzles supplied by ANP will reduce this noise significantly whilst, at the same time, enhancing the blow off force achieved for any given air pressure. For example an air edger using similar air pressure to an open pipe may reduce the noise level form 98 to 74 Db. This 24Db reduction, give the logarithmic nature of the decibel system, means the noise is reduced by a factor 2.4, simply changing the nozzle can result in under a quarter of the noise level.

Air knives and air edgers

Standard air knifes will normally reduce noise by 10dbA which means a halving of noise levels when compared with open pipe systems. The advanced silent x-stream air knives, however, typically deliver 15dbA reductions in noise. The extra 5dbA (compared to standard air knives) may not seem like much but is actually an extra 50% noise reduction. Similar results can be achieved form air edgers.

Air nozzles and air jets

Air nozzles and air jets will significantly reduce noise when compared to open pipe blow off. Overall noise out- put will be in the range of 74 -78 dBA. This compared of open pipe noise levels of 90-98 Dba. So air nozzles will reduce overall noise levels by a factor of 2-3. They will also increase the effectiveness of the air so less pressure might be needed to achieve the same results which, again, will reduce noise levels.

It can often be hard to determine exactly what pressure is required to achieve successful blow off. Testing this with a standard air-line will almost certainly result in a large over estimation of the compressed air pressure required to deliver the necessary force. This is because a standard air-line hose operating at a given pressure will not entrain much of the surrounding air and the resulting air stream will be chaotic and turbulent meaning it will lose impact at a very short distance from the outlet.

Powered blower systems are often bulky. The blower unit will need to be deployed very close to where it is needed and this may not be ideal given the factory layout. What this often means is that optimal factory layout is compromised by the deployment of powered blower units.

In contrast enhanced compressed air systems are small and compact. The air edgers, air jets air knives or air nozzles that produce the air force are relatively small and can be integrated into most production lines taking up minimal space. The air feed system is simply a compressed air line with the compressor itself being situated potentially many 10’s of meters away at a convenient point. Indeed many factories will have air lines and compressors already installed so installation of a blow of system is simply a case of extending the existing air lines to the appropriate point.

One potentially big advantage of compressed air blow-off systems overpowered blowers is that they are able to be cycled off and on very quickly. This means that the air blow-off only needs to be delivered when it is needed. Obviously, this is no advantage when continual blow off is required but with many conveyor based systems the blow-off is only required periodically as the product passes. Connected to a simple solenoid valve system an air nozzle system can be switched on just as the product passes. This can save a considerable amount of energy.

The positioning of air nozzles and other compressed air enhancement products is of critical importance. The different styles of product mean that different factors need to be considered when thinking about positioning.

Air edgers, air knifes and ring blades.

Some products like air blades and ring blades are designed to help remove many of the hassles of position. Due to their shape they deliver air flow along their lengths meaning there is no need to consider the spacing between individual nozzles. The main consideration, therefore, with these products is distance from the target.

The closer the target is to the air knife, blade or edgers the more impact it will receive. There will normally be some practical constraints on exactly how close to the target the air nozzles can be positioned, and, it may be that too much impact is undesirable anyway. The datasheets in the product sections below give approximate air impact data at various distances and supply air pressures. This will help determine where the product need to be positioned for optimal results,

Air nozzle

Air nozzles are designed to produce very focused “spot” jets of air force. So, when an area needs blow off, consideration needs to be given to how far apart the individual nozzles will be. The data sheets will show the approximate patterns and spread of the air flows from different nozzles at various pressures and distances. This will help determine positioning. Also the distance from the target will, like as with air knives, ultimately determine the blow-off force seen by the target.