What’s better, a PD or Fan Combination Unit?

Vac2Go Operation

When renting a vacuum truck and before beginning any municipality or other work which would require a combination unit vacuum truck, it’s important to understand the work you will be doing so you know which type of combo unit is right for you. A combination unit vacuum truck uses high pressure water and vacuum to clear and clean sewer lines and remove blockages. The unit is self-contained with its own water supply tanks, debris body, vacuum system, rodder pump, hose reel, high pressure water hose, and hydraulic pump.

When selection a combination unit, you will first need to decide which style will work best for your job. There are two styles to choose from, a centrifugal fan compressor also known as a “Fan” unit or a positive displacement (PD) unit. With a Fan unit, if the debris body fills to capacity and overflows, the debris is ejected into the atmosphere. Fan units need a higher level of filtration vs. a PD unit. Fan units will push air into the debris body, drawing debris into the suction tube. PD units will pull air out of the debris body, creating more of a true vacuum. If you overfill a PD pump, you can ruin it. Fan machines are most typically “dual engine” units, utilizing both the chassis and an auxiliary engine to power the suction or the jetting functions.

PD Unit

“Fan” or “Centrifugal Compressor” unit primarily uses air movement to lift material and debris up the suction hose into the hopper. Fan units are most popular in straight catch basin cleaning as they handle drier materials well and don’t have the close tolerances found in PD blowers. However, if the debris is mostly liquid as found in sanitary lines, PD machines can be more efficient and can move the material greater distances, especially horizontally. PD units mostly utilize the chassis engine for both functions. Therefore, chassis horsepower has to be considered when spec’ing out your unit.

Fan Unit

Share this Post