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From Behind the Nozzle
By: Leo Waddell
The prep must be done right, but we will leave that for another story. We will try to cover all the wet and dry system. Both require a qualified nozzle man.
I remember 50 years ago (telling my age) when you learned the hard way now with the ASA training, nobody should operate the nozzle without attending an 8 hour class. Some of the important things that will be discussed:
1. water cement ratio
2. wrapping rebar
3. over spray /rebond
4. curing
The nozzle man has other responsibilities besides operating the nozzle. Assuming prep is done if you're going to place concrete on “IT”, pre wet “it”, SSD for repair work. I find from my experience the wet gun boys skip this often but, the dry gun boys do a pretty good job keeping things pre wet though “not always”.
In the wet gun, a two inch nozzle is the most popular but there is a 1 1/2 inch and a 2 1/2 inch available. It is important to have enough volume of air for each nozzle size. A 185 cubic feet at 100 PSI is required for the 2 inch nozzle. The air valve should never be shut off completely and full on except in special conditions. Full on will maintain the velocity for compaction.
For dry gun we will be adding water for hydration in the nozzle. We need 45 PSI air pressure in the nozzle to achieve proper velocity for compaction. Assuming the nozzle tip is ¼” smaller than the hose.
Now we want to inject the water so we need a minimum of 15 PSI greater then air pressure. I like to have my water pressure about 80 PSI so my water hose can't kink and the blowing dust all over while somebody finds the problem. I also turn my water on before the air so I don't blow sand into the water ring.