Every central vacuum system needs a filtration system to protect the motor, and any type of filter installed in the vacuum will impede airflow in some way. The key to an effective filtration system in a vacuum is protecting the motor from damage while still allowing maximum airflow for vacuuming power.
Cyclonic, Inverted Bag and Top Emptying
The diagram above shows the three main methods of central vacuum filtration: Cyclonic Filtration and Inverted Bag Filtration with the motor in the top of the unit, and Top Emptying Bag Filtration with the motor in the bottom.
The term cyclonic simply refers to the flow of air within the unit, where the air flows in a pattern that looks like a cyclone. No systems achieve true filtration using cyclonic power alone, where centrifugal force and gravity separate the impurities from the intake air. Cyclonic systems still need to use filtration to protect the motor.
While cyclonic action does remove the heavy particles, the light fibers and dust can be emitted through the fan blades, potentially decreasing the life of the motor. For this reason, most cyclonic systems must be vented outside of living areas so that the finer particles and dust are not emitted back into the living space.
Whether cloth, foam, geotextile, self-cleaning, or never-clog cloth, all cyclonic systems use filters to try to protect the motor. The cyclonic action does eliminate a high degree of the debris. Therefore, fine dust and lint need to be kept from the motor by the filter, which needs to be regularly cleaned or replaced to maintain maximum air flow and protect the motor.
Inverted Bag Filtration
It should be noted that filtered systems are, in theory, more restrictive of airflow than cyclonic systems. As the trash receptacle fills up with debris, airflow will diminish. Systems with longer continuous power often support a paper bag with a cloth bag, which allows the paper bag to be made lighter and more breathable.
For super-filtration, where extremely fine particles are being picked up (such as aluminum oxide in dental labs, plastic dust in circuit board manufacturing, or sanding debris in auto body shops and marble polishing), a combination of systems has proven most effective. First, a cyclonic separator removes large debris. Then a separate paper bag filtration unit catches the fine particles. A HEPA "micro-filter" can also be installed which filters down to .1 micron at a 99.7% efficiency (1). This will certainly minimize motor failure. However, the finer the filter, the quicker the loss of performance.
Our AirMaster vacuum unit uses Inverted Bag Filtration. It is a hybrid system with two choices of filtration: either disposable Micro-X filtration bags to encapsulate all fine dirt particles, or the pre-installed inverted Microtex cloth filter, eliminating the need for any disposable bags.
Top Emptying Bag Filtration
With this method, the air below the bag (near the motors) is much cleaner than cyclonic models. This maintains vacuum performance and protects the fan blades from build-up which can cause early failure.
Our Modern Day, SilentMaster and Flo-Master vacuums use the top emptying bag method with Tru-Seal Microfiltration that has a 5-ply microfilter closed bag. The bag connects to both intakes and the utility valve, while holding 8 gallons of debris. It can remove particles as small as .3 microns from the air stream without hindering vacuum performance.
The last stage of the secondary filtering is made of breathable mesh, so the high performance motors in the motor compartment are kept clean by the filtration system above it. While vacuums using cyclonic filtration normally need to be vented outside, this top emptying bag filtration system keeps the exhaust much cleaner, effectively removing the need for outside venting.