Hydrovac or Airvac? What’s Better?
Vacuum excavation is growing across Canada as the construction industry and utility owners shift to non-destructive methods to safely excavate around underground utilities and other environmental obstacles.
What was once a sector dominated by hydrovacs, air excavation has grown quickly over the last decade, leading to the obvious question, “Which method is better?”
Everyone in the industry appears to have a robust opinion on this topic. They all have unique motives for a choice for both air and hydro vacuum excavation methods. But there’s no straightforward solution about which method is better. The user must rely on multiple elements including the type of job, work situations and final job goals, in addition to site specifications.
Let’s start with a brief explanation of each method.
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What Is Hydrovacing?
Hydrovacing is the process of removing or moving ground or debris using high-pressure water to cut and liquefy the targeted area of excavation, while simultaneously using an air conveyance or vacuum to transfer the ground or debris to a debris tank of the hydrovac unit. This allows for the efficient (compared to hand digging with a shovel) and non-destructive excavation of soil to expose and verify underground utilities.
What Is Air Excavation?
Air excavation or “soft dig” is a non-mechanical and less invasive method of vacuum excavation. Much like the hydrovac, the air vac simultaneously uses an air conveyance or vacuum to transfer the ground or debris to a debris tank of the unit. However, with air excavation, the operator uses a mobile air vac unit with a hand-held air spade (instead of high-pressure water wand) to loosen soil and break up any large materials. The stored spoils can be transported elsewhere or, unlike a hydrovac, if material is dry, re-used as fill.
When considering using hydro or air excavation to complete a job, there are some key factors to consider before making a final decision.
Which Method Is Faster?
Hands down a hydrovac will excavate faster in most soil types when it comes to the digging aspect of the job, but that doesn’t mean hydrovacs are always faster overall.
The big selling point of an airvac is the capability to dump spoils back onsite and the material can be reused for back filling the excavation. The unfortunate part of the hydrovac, which seems to be its hardest selling point, is the muddy spoils it creates needs to be taken offsite to a disposal location. In most situations the material must be handled by a soil reclaiming company, which may quickly drive job costs up.
Not so fast…just because the airvac can dump spoils back onsite doesn’t mean it’s the answer quite yet.
There are many customers who don’t always allow the spoils to be reused. Reasons include the material is not effective enough for compaction or it’s not suitable to cover older or sensitive utilities. These two examples are directly linked to utility companies having higher standards today than when these utilities were first buried.
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Overall, it’s important to check with the customer to see if the spoils can be reused for backfill before – even if you’ve worked for them in the past – before deciding which piece of equipment is best for you.
Which Method Is Safer?
Safer for whom? Is it the operator or the utility owner?
The answer is: Both.
The method with the least chance of harming underground utilities will be the safer option for the operator and the utility owner overall.
When a particular task calls for digging close to electrical wires, air excavating is recommended because, in contrast to water, air isn’t a conductor. Air excavation is the first choice around critical or delicate job environments, such as excavations that require no harm to tree roots, fibre-optic lines or older and more fragile underground infrastructures. But don’t think air excavation unit cannot damage lines, the chances are just less.
Hydro excavation, with the high-pressure water, can create more damage in some situations, however with proper training it is a much faster way to excavate.
Make no mistake, both methods can be harmful to the utilities and lead to unsafe conditions if the operator is not trained properly. Adequate training is key.
Less Impact on Jobsites
We all know which method creates a greater mess. Hydro excavation is faster, but the water it blasts creates a slurry mess. Air excavation can also be a messy – but in the form of the dust it creates.
Both methods can create public hazards, which should be taken into consideration for each job. For instance, when working in highly populated area it’s important to realize airvacs can create a lot of dust and a hydrovac can create a lot of muddy flying debris.
The amount of airbourne hazards can be somewhat controlled with both methods. However, dust produced by an air excavator is harder contain. It comes down to how well the operator was trained to do the job and the amount of attention they put into the task. Adequate and efficient training always minimizes all hazards.
The ground conditions need to be taken into consideration on every dig site. On sites with loose soil types, such as sand and gravel and those that were pre-dug, the airvac will overpower a hydrovac unit. This is because of an airvacs unique design to vacuum dry material without creating internal machine problems with dusty materials. This includes plugged filters that create overheating issues because of air component starvation, dry material dumping and lack of vacuum.
This is where the hydrovac unit wins in a big way. A hydrovac is more versatile because it can excavate in just about any soil condition or type. Whether it is muddy, hard clay, rocky, sandy or even frozen ground conditions this machine with get the job done. With an on-board hot water heater, the hydrovac unit can dig even the most frozen ground to complete the job. This is one of the reasons why airvac units are more difficult to sell in northern parts of North America.
Which Is More Versatile?
In my opinion, this is another win for the hydrovac unit. The industry will always find different ways to use each piece of equipment in ways to help move along the jobs with ease. Because of the on-board components that the hydrovac unit is equipped with, I believe it can be more versatile. For instance, the water it carries can be used for pressure washing and the hot water heater can be used in many ways for cleaning and steaming or even thawing frozen objects.
I believe as airvac units grow in popularity the industry will find many more unique ways to use them.
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To create an apples-to-apples comparison, let’s say a particular job requires the spoils – regardless of method used – to be hauled to a disposal site. There are some key points to take into consideration.
Water in the debris tank is unavoidable with a hydrovac. On average, 20 to 30 per cent of a load is water depending on ground conditions, soil type and even an operator’s level of experience.
An airvac’s debris tank fills with mostly dry material from the dig site. This means even if the airvac is a bit slower getting the load on, it will be more effective when it comes to volumes of material removed from a jobsite in a single load.
Weight is a big concern in terms of increased disposal costs as most facilities charge by the weight of the load. Because the hydrovac’s debris is a mix of soil and water, the sheer weight of the material is heavier. Additionally, it might be more difficult to find a facility that can accept wet spoils. Speaking of weight, it’s important to be aware of local DOT regulations, and that the operator is cognizant of their load.
Again, do your research and compare resources and costs.
Expense of the Unit
Now this is where it gets complicated, as I mentioned the airvac can sometimes do the job faster and less expensively because of the ability to dump onsite. However, the problem lies in the expense of the airvac unit.
A true airvac unit is just about double of its competitor, this means the rate an airvac operator charges for being dispatched to a job will be greater than that of the hydrovac. This does not mean a hydrovac is always less expensive to hire, highlighting the need to properly weigh the differences for each job.
It’s best to pre-estimate all the resources it takes to complete a project. This includes disposal of material, costs to refill a hydrovac with water and the cost of material to fill, as well as associated transportation and energy costs.
With the airvac being a newer option in the industry, I would have to say the hydrovac is less expensive to maintain.
There is more equipment and resources available, as well as parts centres and knowledgeable repair facilities. This means the hydrovacs can get back on the job and keep profitable more quickly. Because of an airvac’s unique design, it is an advanced package with many moving parts and technology, hence the higher price tag. This often means an owner will probably spend more time and money in maintenance.
A good understanding of the unit’s components and better trained operator, coupled with a good maintenance program, can keep these costs to a minimum.
So now knowing all these key factors is it clear which option is better overall?
The answer is: There is no one option that is better overall. Each method brings great options to the table. Ultimately, there is a place for both vacuum excavation methods across North America.