Typically you will find that the cyclonic units are the ones with the motors on the top.  They bring the dirt in the side of the unit, spin it around with a cyclonic action, and rely on gravity to drop the major portion of the dirt out of the airstream and then pull the air off of the middle of the cyclone that is created.  Some of them then locate a filter in the middle of this space.  MD’s paper bag system prefers the motors on the bottom for the following reasons:

1. Each vacuum motor typically employed in central vacuums contains a separate cooling fan that draws air into the motor to cool it.  They do not rely on vacuumed air to cool the unit.  In the event that there is ever a clog in the system, a central vacuum will not burn its motors up as long as it has this intake cooling air.
2. The location of this intake cooling fan is critical.  If it is located on the top of the unit it will draw air from around it.  For units with the motor on top, it draws this air from the hottest portion of the unit; where the hot air exhausts.  On the MD units with the motor on the bottom, this air is drawn from the very bottom of the unit; the coolest air location.
3. If the motor is also located up high in the garage and this motor is on the very top of the unit, it is operating in the hottest portion of the garage.  MD’s motors on the bottom of the unit, are located very close to the floor, thus also drawing from the coolest resource of air available.  Hot air rises thus a unit with the motor on top runs hotter than one with the motor on the bottom.
4. Typically cyclonic units are located about eye height.  This puts the motor much closer to the user’s ear as opposed to MD units with the motors down near the ground, further from the operator’s ear.
5. All of the cyclonic units (with the motor located on top) have some sort of filtration system.  Either you have to pull a cloth bag down and shake it, clean out a cartridge, or reach up to scrape off a screen.  With the MD unit you simply lift a lid, wad up a paper bag and dispose of it.  You are always back to a brand new filtering system once you change the bag.  With the cyclonic filter types you are never back to the original pure filtering system (unless you replace a cartridge.)
6. The key to MD’s filtering system is the cloth bag behind the paper bag.  This allows a much more porous paper to be used as the strength of the bag is maintained without compromising suction.  The supporting cloth bag is tapered, thus the air is not sucking through the trash but through all the pores simultaneously.  The air is rather turbulent when it enters the bag and actually “scrubs” debris off the sides of the paper bag.
7. Once the paper bag is full on an MD unit it begins to loose suction.  On many of the units with the motor on top, when the unit is full it will then allow the debris to suck directly into the motor.
8. On most units that have the motor on top, the cooling fan intake is located on the top cover of the unit.  Often we have seen that homeowners will place a box or other object on top of the unit inadvertently believing this to be a convenient storage location.  Unfortunately that box then completely blocks the cooling air intake and the motor will prematurely fail.  Having the motors on the bottom, MD units mount 6” off the ground and thus the cooling air intake is extremely difficult to accidentally block.

You might also read our article “Filtration Analysis” located at: http://builtinvacuum.com/filtanal.html

This entry was posted on Thursday, February 28th, 2008 at 2:18 pm and is filed under About MD, Business Practice, MD Products, CV Facts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.