HIGH VOLUME vs. HIGH PRESSURE
SCAND TECH EQUIPMENT HIGH VOLUME NOZZLES
Our compressed air cleaning equipment is based upon the use of high volume air (40-185 Cubic Feet Per Minute- CFM’s) and medium pressure (90- 120 Pounds per Square Inch- PSI). Most of the companies in our industry have been using low volume (15-25 CFM) and higher pressure (175-250 PSI) air whips and nozzles.
The main difference in these two methods is best described by the following example: If you were to hook up a garden hose (½”) to one side of a fire hydrant and a fire hose (1 ½ “) to the other side, both hoses would be supplied with the same pressure (60 -80 PSI in most streets) but the volumes would be different. If you were moving the dirt on your drive way, the ½ “ hose would become ineffective when the dirt built up a few inches and could no longer be moved. The larger volume hose would have no trouble moving any of the dirt and would do it 5-10 times faster. This same principle applies to the dirt load in duct systems.
Breaking the dirt loose from the duct wall is accomplished by brushing or air washing. Moving the dirt down the duct is accomplished by the “air speed” and volume of air movement inside the duct. Using a vacuum collector to move the air, in the duct, does not generally provide enough “air speed” to keep the contaminates moving in the air stream. Like the example above when the low volume water hose stopped moving the dirt, low volume air and low air speeds allow the dirt to drop back down a few feet from the nozzle. This eventually builds up to piles that are not easily moved. High volume air nozzles increase the air speed to a point where most of the contaminates can be put into an air stream that will carry them all the way to the collector, even when they are hooked to ducts up to 100′ long.
About your concerns about putting too much air into a duct system and overpowering the collector.
If a vacuum collector is rated for 2500 CFM’s (just an example), the rating is at the “throat” of the collector. After a hose is connected from the collector to the duct (10′ for example), the static resistance reduces the CFM’s. Depending upon the length of the duct you are working with, there is a further reduction in the CFM’s. If the static reduction is 10-20% (very typical) of the 2500 CFM collector, then it is 250- 500 CFM’s below what the collector can consume. Our nozzles will flow 40 to 150 CFM’s depending upon the size and style used. This is well within what a collector can handle. In a 16″ x 16″ duct, our 1″ nozzle ALONE, with no collector pulling air, will produce an air speed of over 2500 Liner Feet Per Minute (FPM). (NADCA minimum, ACR 2005 18.104.22.168)
There are also concerns with “seams leaking” from the air pressure. The low volume air tools usually are run using small compressors at 175 – 225 psi. The high volume tools need “tow behind” compressors 100 -185 CFM. Depending upon the manufacturer, they are set between 90 to 120 PSI. Either of these combinations will cause some air to be released if the nozzle comes in direct contact with a bad seam. A lot of customers want to know where these leaks are so they can be sealed because if the air used for cleaning is leaking out, so is the conditioned air that they are paying for on a daily basis.
If you have a pile of dirt that you have to move, you could use a teaspoon. …… or…
If you want to do it effectively, efficiently and economically use a shovel !
If you have a pile of dirt in a duct to move, you could use a 1/4″ skipper or a hit and miss air whip … OR
If you want to do it effectively, efficiently and economically use our High Volume Nozzles…………