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SYSTEM OPERATION AND MAINTENANCE
Cause: Insufficient compressed air. This could be the result of using an undersized or defective air compressor, using the wrong size air lines for the length of run, leaky air lines, or a valve which is obstructed or not opening all the way. The pressure reading on the compressor is not relevant to the air flow at the pump.
Problem: Unit does not perform well and pressure gauge (on the pump) reads in the normal range (over 68psi).
Cause: There are two probable causes: 1) the system may have a vacuum leak at one of the seals. Other places to look for leaks are along the material handling hose. 2) the second cause may be dirt buildup in the vacuum generator, a clog in the material hose, an over full hopper, or an extremely clogged exhaust bag. If the unit does not generate much vacuum or flow, the neoprene flapper (check) valves in the base of the vacuum generator may be in need of replacement.
Problem: Air lance does not cut through the soil.
Cause: Check the air flow from the blade end of the lance and make sure it is not clogged with dirt. If the lance blade air gap is too wide or too narrow it will not dig efficiently. Check the air gap, it should be approximately .040 in. for proper operation. You may also have encountered very hard soils and you may have to alter your technique. It is usually more effective to bore pilot holes in hard soils than to jab into them with the blade. GENERALLY YOU SHOULD NOT USE THE LANCE TO DIG THE FIRST 12" OF EXCAVATION. THERE IS TOO MUCH RISK OF INJURY FROM FLYING MATERIAL. USE A DIGGING BAR OR OTHER HAND TOOL FOR THE FIRST 12" OF EXCAVATION AS LONG AS YOU ARE SURE NOT TO ENCOUNTER UTILITIES.
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.
