A real Compressed Air Pulsing System
The Challenge, Guidelines, Real Results and Applications
Air has been pulsed for years using solenoid valves to go on and off at pre-set frequencies which has the goal of reducing compressed air consumption by only allowing the flow of compressed air when needed, typically for a blow off or cleaning application. The limitation in using traditional solenoid valves was their design in that at higher frequencies, vibration becomes an issue affecting the life of the valve. Efforts appear to have been concentrated in reducing this vibration with valve modifications resulting in better quality valves, but nevertheless, they are modified solenoids with no dramatic design changes as to their operation. Then they are marketed specifically for compressed air pulsing with claims of reducing the overall compressed air use down to 50%. But the question remains is if this is a valid claim.
It is important to remember that compressed air is not a liquid. It is a compressible fluid and as such behaves differently than a liquid. When compressed air is used steadily, the flow will settle to a consistent flow rate and velocity. When pulsed, the air gives a bit of a “kick” at the outlet which causes some effect upstream that with traditional solenoids had to address as vibration. This “kick” is a slight increase in force as the pulse begins. This action, plus the on-off pulse causes the scrubbing action can increase cleaning and drying ability, or supposedly can. However, there are some issues with these designs that for all the searching of literature does not seem to address.
First is the claim that savings can be up to 50%. Investigating several studies done with the system the savings varied significantly with the best coming to about 30% and some applications minimal.
Secondly, in many cases the average force developed at the outlet, an important factor for any blow off application, goes down by as much as 50%. In fact, the force can drop so much that even with the extra “kick” from the pulse no longer performs the job. If it was performing the work at 50% force, the application can just as easily reduce the line pressure by 50% and save almost as much energy without the need of the pulsing unit.
One product tested was a pulse system built into an air gun. Most air guns tend to have long length of inlet hose or tubing and the force tested dropped significantly to near 50% of the force at continuous flow. In addition, holding the air gun was rather irritating with even a mild vibration from the pulsing action.
There appears to be no guidelines for installation and consideration of dealing with the peculiarities of compressed air that need to be addressed which may be the primary reasons for these wide variations. It may also be the reason that despite the wide publicity of pulse systems, they are not as yet widely used. No one appears to be running out to purchase one.
When compressed air is turned on and off at high speeds, you have essentially a “jerking action” in the flow which means a large velocity. This creates a pressure loss as normally piping would be sized for continuous flow. This could be one major reason for the wide variation in performance. After all, if all one needs to do to meet the same performance of a pulse system
by merely reducing the system pressure it is much less costly to use an air regulator. Similarly, air amplifiers such as air jet and air knives are still widely used that convert pressure to flow, creating less force but maintaining a high flow and kinetic energy, while reducing energy, again with much less product cost.
Another trend in the past year has been the use of amplifying nozzles with pulse systems that actually improved the system performance.
The other limitation is that these pulse systems are set to pulse at a certain frequency and a separate control valve is needed for on off control when the air is not needed. An example would be on a packaging line were you want the air to blow (and pulse) when the product is there, and to stop when the product is not there. A system to incorporate both the pulsing action and on-off action as needed would be far more compact and efficient and would only need a sensor.
The line speed of what the pulse system is addressing is very important. Existing systems limit the pulse to 15 hz. So for very fast line speeds where compressed air is used for drying or cleaning, it would not work as spots could be “missed” during the non-air flow phase.
All the preceding reasons could be reasons for the limited use of compressed air pulse systems. The ideal system would be valve that does not act like a typical solenoid valve, and can pulse at higher frequencies, combine an option for on off control as part of the system, is less sensitive to the back pressures part of
the installation and offered with a clear set of guidelines for installation to minimize the back pressure.
One such system is now available – The AirFlow Saver from KTW Technology. A revolutionary valve uses a totally different system – SmartValve Technology, which was for the space mission Rosetta . It can pulse as much as 40 hz. Unlike previous solenoids, and modified solenoids used in previous pulse systems, the valve operates stochastically in a simpler, rugged, long lasting design with fast response time not seen before in previous valves. Old solenoid valves and even modified ones require relatively frequent maintenance. The new valve design does not. One important by-product is a significant higher instantaneous pulse force when installed minimizing back pressures. The other effect of the valve is an average force that is actually higher than the force of a steady air flow. So even with significant back pressure considered, the system is much less sensitive to having the average force reduced than any previous pulse system. The flexibility of the valve is enormous. A specially developed electronic system allows the opening and closing time of the valve to be individually controlled in real-time, allowing each application to be individually optimized.
Once the frequency desired is set, it also has a built in on-off control to stop flow and pulse when not needed utilizing a sensor. Installations have shown these systems to reduce energy close to 50% with continuous operation and with on-off control operating for discreet blow of application, 95% on one specific test.
The large “point force amplification” opens up a great deal of potential applications. Apart from very high scrubbing action there may be applications where air is used in mixing. Set guidelines have also been set for installation to minimize any back pressure effects. When this point amplification of force occurs, there is a force that also extends back up the air system that is much greater as well than precious pulse systems. A dampening attachment is inserted at the inlet of the valve to eliminate any negative effect from that travelling wave of force. The valve design itself is rugged to withstand the high frequency operation and forces involved.
Another advantage offered by the force amplification is that compressed air pressure at the inlet can often be reduced another 10% or more saving even more energy if the amplified force is not needed. This system truly offers the potential for not only better cleaning or drying but significantly greater energy reduction
than previous systems. The system has been tested and applied with amplifying nozzles and even air knives. Firm parameters are set for installation and line size depending on the nozzles used and also for the type of air amplifying attachment such as air knives. Air amplifiers are recommended as they enhance the air blow off effect by extending the effective distance of the blow off and further reduces energy use as well as reducing exhaust noise levels. The system has literally the
potential to reduce the energy use to the level of an electrically operated blower without the high maintenance costs and space restraints that blowers have in many applications, and yet provide greatly enhanced cleaning and drying power.
One important factor is the types of nozzle or any attachment that is used for the exhausted compressed air. Due to the force amplification air nozzles should be one piece design and metal as the pulsing could lead to early failure of plastic parts usually glued together or two piece nozzles. Tests with plastic air jets for example resulted in the breaking of the plastic pieces. Stronger metal attachments are recommended. In addition, holes in nozzles produce different results and can affect the pulsing action. However, guidelines are provided. Air knives also work well up to a certain length depending on the pulsing frequency and pressure.
Immediate applications for the units are as follows:
1. Drying of bottles, cans, packages on high speed lines. Here the new units can effectively reduce the compressed air use by 50% or more, especially as pressure can be reduced since the higher force amplification effect may not be required.
2. Combined with air knives or air jets or air amplifiers and static elimination technology, the pulsing and force amplification produced can better clean parts such as auto bodies, door panels, and bumpers than current blow off systems and potentially with even less energy use than a blower system. This is very significant in that much of the industry originally moved away from more quiet and simple compressed air amplifier systems with static control to noisier, higher maintenance blower systems primarily due to energy concerns. This could be completely reversed back to compressed air with these pulse systems. There has been some movement to the use of compressed air operated rotary nozzles, with and without static control for cleaning using the pulse action caused by these rotating nozzles. However, the collection and removal of the dirt cleaning with rotary nozzles is far more difficult. Using rows of nozzles or air jets or air knives with a pulse system is much easier because you basically have a clean side, and a dirty side as the part moves under the cleaning system via a conveyor. This also eliminates the maintenance required on rotary nozzles which have bearings and will be subject to wear.
3. The semi-conductor industry requires very clean parts and pulsing is something that has been investigated and sometimes used. This new system can potentially both improve quality and reduce energy costs.
4. Part ejection using compressed air is normally limited to lighter parts. With the force amplification effect, heaver parts can be ejected and with less energy due to the pulsing action.
5. Mixing and aeration where compressed air is used might be improved using pulse action. A great deal of compressed air is used in such applications and the high force amplification effect may help reduce energy costs in such applications.
6. The furniture industry blows the edges clean from sawdust after cutting the panels. The edges are then glued. Effective cleaning is very important as it reduces waste. The removal of particulate from wood is particularly difficult due to the sticky nature of sawdust. The pulsing action can greatly improve cleaning due to the scrubbing action. Cleaning of melamine board requires static elimination as well which air knives and pulsing can better address.
7. Plastic and rubber injection molded parts are removed from the molds with the aid of compressed air and scrap pieces also need to be removed. Rapidly pulsating shocks accelerate the removal process and is sometimes aided with static elimination.
8. Fruit and vegetable sorting machines blow low-quality goods from the sorting plant. High pulse speeds and increased pulse force improve the speed and efficiency of the sorting process.
9. Die casting and milled parts are cleaned by compressed air after production. An efficient cleaning with optimization of the blowing time and with the increased force enhances the operation. For example, the extra pulse force and pulsing action itself can loosen parts that may be stuck where a steady blow off cannot.
10.Higher pressure nozzles in the range of 300 PSIG are being developed where liquid cannot be used and high force is necessary in the range of 10 pounds force and above. The pulse system can handle such high pressures and can potentially improve the performance and force of high pressure nozzles as well. The mining industry in particular could find this application useful.
The applications described are certainly only a small excerpt of the possibilities in which the use of the AirFlowSaver generates added value. Wherever compressed air is used for blowing and cleaning, it can be useful to consider the use of SmartValve technology. Savings between 50% and 95% of inefficient compressed air, which is 8 to 10 times more expensive to produce than electricity, speak for themselves. The sustainability certificate and the energy balance of a company will in future be a further criterion for customers and in the external image. The AirFlowSaver is a solution to increase efficiency, reduce energy costs and the Co²-quota. German industry spends 4.5 billion € per year alone on energy costs for the production of compressed air. Since at least 50% of the compressed air is used for blowing applications, the potential for saving energy costs is in the billion € range only in Germany, and not to forget many million tons of CO².