With the sophistication of modern hydro excavators, it’s easy to overlook the importance of the potholing nozzle on the end of the wand. However, subpar vacuum excavation performance can often be traced back to nozzle choice. Nozzle rotation, spray pattern and size influence cutting performance and water usage.
“When it comes to potholing and hydro trenching, productive digging and efficient water usage help crews maximize their time on the job. An often-overlooked component of a vacuum excavator is the nozzle a crew uses to dig with. It can significantly impact digging performance and the volume of water used during the process,” said T.J. Steele, product manager for Vermeer MV Solutions.
Excessive water use adds to labor requirements. Oversaturating material during the digging and excavation process requires water tanks to be refilled and spoil tanks to be emptied more frequently, stealing time from the crews.
Match pump and nozzle size for speed
The solution is to select the best size potholing nozzle for the application. Unfortunately, crews often choose a potholing nozzle based on past use instead of matching it to their specific vacuum excavator pump size. A mismatched pump and nozzle affect the productivity of the overall system. One symptom of this is excessive time daylighting utilities.
“Nozzle sizing is a big education issue in this industry. Too small of a nozzle can reduce efficiency. If the nozzle is too small, the unloader valve will divert the excess water flow produced by the water pump,” noted Steele. This could also slow production rates.
Nozzle size and pump pressure determine the flow rate. A number 5 nozzle will flow about 4.3 gpm (16.3 L/min) at 3,000 psi (20 MPa), and a number 10 nozzle will flow 8.7 gpm (32.9 L/min) at 3,000 psi (20 MPa). You want to have a small amount of water bypass to help prolong the life of the unloader valve. A 10-gpm (37.9-L/min) pump with a number 5 nozzle only uses half the available capacity at 3,000 psi (20 MPa). In this scenario, the water pump bypasses half of the vacuum excavator’s water pump potential back to the tank. The nozzle then becomes the limiting factor in overall performance.
In most cases, you should base nozzle size on water pump size and pressure. But there are other factors to consider.
“If you have a 10-gpm (37.9-L/min) water pump, you can run up to a number 10 nozzle and still maintain pressure. But operating a number 10 nozzle all day can be challenging for the operator and cause fatigue. That is why many operators opt to use a number 8 nozzle,” explained Steele.
Consider time savings versus water use
“Operators concerned with water use will often use a smaller potholing nozzle. Their theory is that a smaller nozzle restricts water flow. However, this approach may not lead to the desired water savings depending on soil conditions. A higher flow nozzle may be able to dig more quickly for faster daylighting of a utility,” said Steele.
It may take the same amount of total water to complete the potholing operation with either nozzle, but you just complete it in less time with the larger nozzle.
The design of the potholing nozzle can also affect the amount of water required. For instance, the Vermeer QuickDig™ nozzle helps save you time and water, making it up to 35% more efficient than a traditional rotary nozzle, according to manufacturer-provided performance data. The QuickDig nozzle rotates at a slower speed than other hydro-excavation nozzles, which helps increase its digging power and control while minimizing wear.
Spray pattern determines performance
The spray pattern helps determine cutting performance and the appropriate applications for a nozzle. For instance, most home pressure washers offer 15- to 25-degree spray patterns, while the most powerful spray pattern is 0 degrees. But, that volume of force being concentrated on a small area has major drawbacks. It is not recommended as a potholing nozzle because it can damage some utility lines.
An effective potholing nozzle features an 18-degree cone of coverage, like the Vermeer QuickDig nozzle. This nozzle’s design promotes laminar flow with all water molecules flowing in the same direction at the same speed to efficiently slice through the ground. And, the rotating aperture helps to mitigate the risk of damaging utilities.
Consider nozzle life
Potholing nozzle life will vary based on operator usage and environmental factors. Many state and local regulations require nozzles to have a nonconductive coating when digging near certain utilities. This means nozzles may need to be replaced more frequently.
“The life of the nozzle internals varies a lot, anywhere from a few weeks to a few months, depending upon the crews and how they dig,” said Steele.
But not all potholing nozzles are equally constructed. The Vermeer QuickDig nozzle features a durable design, with a stainless-steel body and tungsten carbide nozzle tip.
It can be rebuilt in the field quickly using a QuickDig nozzle repair kit. With a rotating nozzle, it is time to rebuild or replace it when internals stop rotating or the rotation becomes intermittent. You may get two to three rebuilds out of a nozzle.
Make an informed decision
Selection of the correct potholing nozzle requires knowledge of your vacuum excavation unit and the application. Vermeer offers a nozzle sizing chart that guides you to the ideal choice. Simply identify the water pump size and the pressure and the chart will help you determine the ideal nozzle.
Vermeer offers six sizes of the QuickDig nozzle for you to choose from. Each comes with a .5-in (13-mm) inlet connection (common on truck vacs) and a .25-in (6.4-mm) adapter (common for trailer vacs).
A Vermeer specialist is always available to help. Contact your local Vermeer dealer for more information about Vermeer vacuum excavation equipment.
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