Utility Contractor

SEP-OCT 2018

As the official magazine of NUCA, Utility Contractor presents the latest information affecting every aspect of the utility construction industry, including technological advancements, safety issues, legislative developments and instructional advice.

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Vacuum Excavator Usage on the Rise A Better Way to Locate Buried Utilities By Reed Munro 22 Utility Contractor | September/October 2018 W ith congested underground easements and roadways, it is becoming increasingly important to visually identify the location of underground utilities — gas, fiber, water, telecommunications and sewer — to prevent an accidental utility strike. However, using a compact excavator or a shovel to expose the line could also damage a utility. To reduce the risk of damaging existing utilities, underground contractors and have started using vacuum excavators. According to Jake Jeffords, director of sales and marketing for NUCA member and National Silver Partner McLaughlin Underground, the increasing number of buried utilities that occupy the rights of way of city streets is the driving force behind the expanded use of vacuum excavators. "On almost every utility job, the contractor must expose any buried lines that a new installation may cross to help avoid unknowingly striking an existing utility, and using a vacuum excavator is an efficient and nondestructive way to do that," Jeffords explained. The use of vacuum excavators extends beyond exposing underground utilities. In addition to HDD crews using them to suck up the mixing fluids used while boring, vacuum excavators are being used by municipalities and sign installers to helps minimize restoration work after a hole is dug. "To get the most from these machines, contractors should take the time to understand how vacuum excavators work and the different options available on the market today," Jeffords suggested. How It Works Vacuum excavators use high-pressure water or compressed air to penetrate and break up soil and the unit's powerful vacuum to remove the loose material. Inches of mercury, CFM, cyclonic filtration — these are all associated terms that help explain how a unit will perform in the field. To make sense of all the specifications, it is important for a user to have a basic understanding of technical components, including blower type, volume of air and pressure being created. Vacuum Blower ■ There are two primary types of blowers in vacuum excavators: Positive displacement and centrifugal units. ■ With positive displacement blowers, air enters a blower and is trapped against a cylinder until it is forced — or displaced — through a discharge pipe. This type of blower is becoming the most common for potholing due to its ability to maintain velocity and airflow when in operation. ■ A centrifugal blower typically uses rotating impellers or blades to increase the pressure or the air before discharging it. Volume of Air ■ The term "CFM" stands for cubic feet per minute and is a measure of the volume of air being moved. ■ For optimal performance, the CFM specification on a vacuum excavator must be in direct correlation to the diameter of the hose on the machine used. ■ Optimal hose size will depend on the type of spoil most commonly being removed. ■ Cobble, for example, will be easier to remove with a 4-in. (10-cm) or larger hose and will require a larger blower. Less challenging ground conditions might only require a 3-in. (7.6-cm) hose and less CFM. ■ The key is having enough velocity so the spoils that enter the hose are suspended until they reach the tank — if the material settles in the hose, it could clog the system. Pressure ■ Inches of mercury (psi) is a unit of measurement for pressure. It is more or less a function of how much material the vacuum excavator can move, or lift, at a

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