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There are two approaches to vacuum excavation, dry (air is used to fracture soils), and wet (water is used to break up soil). Both dry and wet methods will work in most circumstances.
Dry Vacuum Excavation
Dry vacuum excavation systems (often called “air-vacuum excavators”), were introduced in the late 1950’s. Before the invention of the VE-75, air-vacuum systems were much more expensive than water jet based systems. Traditional air-vacuum systems need large, high horsepower (and delicate) vacuum pumps, complex filtering, cyclonic separators and a stand alone air compressor to operate the air lance (air knife). The introduction of the VE-75 changed all of that because it operates from a single 185 CFM air compressor and doesn’t need a delicate engine driven pump, filters, separators, or the large truck needed to haul them around.
Wet Vacuum Excavation
Wet vacuum excavation makes use of a pressure washer to break apart soil. They appeared around the time directional drilling for utility installation became popular. Directional drilling creates waste drilling mud which must be recovered, and vacuum systems were ideal for this task. It was soon discovered that by pairing a power washer with a mud recovery vacuum a simple vacuum excavation system could be had for less than the cost of a traditional dry system.
Why Choose Dry Type Air-Vacuum Excavation?
The dry air-vacuum method is definitely the preferred system with those who have experience with vacuum excavation. This is due to certain weaknesses and disadvantages inherent in the wet systems.
A limited on board supply of water means limited digging time. 100 gallons of water only gives 25 minutes of dig time at the typical flow rate of 4 GPM.
Excavated spoils are in the form of mud and can not be used to refill the hole. A separate truck with dry fill must be brought in for each excavation.
A place must be found to empty the spoils tank.
In cold climates antifreeze must be placed in the water tank to prevent it from freezing.
The area around the excavation becomes very messy and slippery.
High pressure water can damage utilities and remove protective wrappings.
If a hole must be dug in pavement a separate air compressor must be brought in to operate a pavement breaker. >
Those familiar with portable vacuum systems know that a four inch vacuum system is by far the most practical size for ease of operation and efficiency. Three inch systems are extremely prone to clogging, while six inch systems require large amounts of horsepower.
A four inch system must develop at least 800 CFM of vacuum flow in order to be effective at lifting heavy materials like rocks.
At the same time, pulling liquids and thick slurries requires high vacuum.
The Utilivac® System is designed to provide both. Air flow of 850 CFM and static lift of over 22" mercury produce impressive results.
How The System Works
The Utilivac® is a precision arrangement of cascading air ejectors and differential inlet control valves resulting in air flow amplification and vacuum. Each sub-assembly is carefully machined from tempered aircraft grade aluminum stock to tolerances of .001," resulting in a nearly indestructible vacuum generator.
The internal geometry and dimensions have been carefully optimized through computer modeling and prototyping, then perfected through thousands of hours of field trials. The result is a system which is amazingly efficient at converting the energy contained in compressed air into useful vacuum flow.
