Regarding the article on locators and vacuum excavators in  Trenchless Technology, December 2008, I would like to clarify some of the erroneous details that were published.

Under “Selecting the Right Unit,” the author never mentions the very important differences between a fan unit and a positive displacement (PD) unit. While a fan unit works in most applications within 100 ft of the truck, it loses suction outside of this range. Also, the fan units require air flow to maintain suction while the PD units do not. We chose to go with PD units as we felt they offered more versatility than a fan unit. We have utilized these PD capabilities in applications up to 600 ft away from the truck with no degradation in suction. I would advise any would-be purchaser to become familiar with the soil types and areas in which one might be potentially excavating. This is very specialized equipment that is not cheap and I would hate to hear that someone bought too little or too much equipment for their particular market application.  

Currently, available vacuum excavation equipment range in sizes much larger than stated in this article. For instance, we have equipment outfitted with 12.5 cu yds debris tanks (approx. 2,500 gals), 1,300-gal water tanks and a 5,150-cfm vacuum. Remember, more spoils capacity plus more water capacity equals less trips to dump spoils and refill water, resulting in savings in both time and money.

It was also referenced that in areas without rocks, a 575-cfm system with a 3-in. hose will suffice. I seriously doubt that a 575-cfm system would prove productive in a clay environment. We have found that digging in clay is best approached with the usage of heated water and a high-powered (5,150-cfm) vacuum.

Another benefit to having an on-board heater, especially in the north, is the capability to work in the winter months and the ability to cut through frost/frozen soils. We work year-round and can excavate when conventional excavation equipment is parked for the winter. In addition, our company initially looked at purchasing “air only” equipment and I am so grateful that we took the time to see both technologies demonstrated. In terms of productivity, the differences between air equipment and water equipment are night and day. Water really loosens up the soil for much more rapid extraction than using air.  hanks for allowing me to voice my opinion.

Jeffrey A. Hines, Hydrovac Resources Inc., Ballston, Spa, N.Y.

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