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SYSTEM OPERATION AND MAINTENANCE
Part 5: Tips for Using the Air Lance and Vacuum
When practical do not use the standard air lance to dig the first 12" of depth. Not only is this dangerous to the operator and passers by, but the first 12" of soil can be very hard and compact. It is better to select a digging bar or other appropriate tool such as a “clay point” lance to break up the hard top layer, and use the vacuum to remove the broken soil. It is a good idea to know the approximate depth of the target utility. If you suspect the utility is less than 2 feet deep you may have no choice but to begin your excavation with the air lance so as to not damage the utility
Never push the standard air lance into the soil without the air turned on. This will clog the tip. A handy tool for unclogging the tip is a piece of hacksaw blade (Figure 20) with the teeth ground off. Make sure there is no pressure behind the lance before you try this. Disconnect the air lance from the air supply to be sure. Make sure that all connections in the lance are very clean. This will keep the connections from leaking.
In very hard soil, add about a gallon of water to the test hole after it is about a foot deep. Then use the lance to drill a pattern of pilot holes and allow the water to combine with the cuttings in the hole to form a slurry. Once you have drilled five or six pilot holes this way, you should be able to break up the hard pan and continue on down to the utility. If you are working in difficult soils contact the factory, there are several different types of air lances available to handle problem soils such as hard pan or tight clay.
In frozen soil, use the pilot hole method to break up the frozen soil. Gently "dance" the lance over the
frozen soil. Do not force the lance or drive the lance into the soil; let the air do the work.
For valve box cleaning, start by using the air lance to loosen the dirt; then apply vacuum and air lance
at the same time to complete the process. You may find that a 3" pickup hose works better.
In frozen soil, use the pilot hole method to break up the frozen soil. Gently "dance" the lance over the frozen soil. Do not force the lance or drive the lance into the soil; let the air do the work. For valve box cleaning, start by using the air lance to loosen the dirt; then apply vacuum and air lance at the same time to complete the process. You may find that a 3" pickup hose works better.
In very sticky mud and clay use the vacuum alone to pull up "plugs" by taking advantage of its high vacuum capabilities. Push the vacuum pickup pipe into the soil then pull it out and allow the plug of soil in the tube to be pulled through. Caution, when the plug comes through the pipe, it will be moving fast. This can be a very effective technique. Some types of clay soils can be excavated using a “clay point” style air lance. Call the factory to discuss which lance is best for your soils.
In very unstable soils, you may need a casing pipe for the spot hole to prevent cave-ins. A section of 6" or 8" plastic pipe works well for this. Before using a casing pipe, it is best to pre-locate the utility with your air lance to make sure you don't waste any effort. It may not be possible to remove your casing pipe from the hole.
Attempting to empty the hopper by tipping it forward is not recommended. A full hopper can weigh in excess of 900 pounds! Open the lower door and remove vacuumed material with a shovel, as shown in this photo. Once the hopper has been shoveled out, the hopper can be tilted forward to completely empty it.
Figure 20:
A hacksaw blade with the teeth removed is a good tool for clearing a clogged nozzle. Relieve all air pressure in the lance before doing this.
