| Finally the homeowner can learn the little tricks of | | | | what creates the needed vacuum (venturi) to |
| the cleaning trade that the professional power | | | | draw the chemical and mix it with the water flow. |
| washing contractors have been using for years to | | | | Changing the size of the discharge orifice |
| make their work look better, go faster and be | | | | regulates the water velocity. This is most often |
| more cost efficient.The application of chemicals is | | | | accomplished using a roll over valve, a double |
| one of the longest standing controversies in the | | | | nozzle head (see page 4), or a dual lance wand |
| power washing industry. There are just as many | | | | (see page 12). Most manufacturers of these |
| opinions on the correct method of doing so as | | | | injectors claim that their draw rates are from |
| there are chemical applicators. The one thing most | | | | 10% to 20%. With a few exceptions, I have |
| contractors seem to agree on is that no single | | | | found this accurate. The problem with this is that |
| method will serve all circumstances efficiently. Of | | | | many people are requesting a draw rate in |
| all the different methods, the three most often | | | | excess of 50%, which is only available with an |
| used are 1) down stream injection [after the | | | | injector that is especially designed to fit at the |
| pump], 2) chemical before the pump [through the | | | | end of a spray lance (see page 13). The problems |
| pump], 3) and the chemical applicator pumps.Each | | | | with this injector are cost and due to the location, |
| of these methods has their benefits as well as | | | | it's a cumbersome package to handle for some |
| their limitations. Down stream chemical injection is | | | | applications. The contractors who most commonly |
| most often used on cold pressure washers | | | | request higher draw rates are ones who are |
| because of low cost and the ability to turn the | | | | applying chlorine to exterior surfaces such as |
| chemical on and off at the wand. Chemical | | | | buildings, decks, and fences. The reason for their |
| injection before the pump is most often used on | | | | concern is that the strongest concentrate of |
| hot pressure washers because of the ability to | | | | sodium hypochlorite (chlorine) available is 15%. |
| apply chemicals with hot water, which makes | | | | When this is mixed at a 10% to 20% ratio in the |
| them more effective. And chemical application | | | | injector, many people feel that it is too weak to |
| pumps are used where the chemicals are not | | | | adequately clean and remove mildew. From this |
| compatible with the pressure washer.The down | | | | springs another question, the advisability of using |
| stream injector is the most common to the | | | | chlorine as a cleaning agent to begin with. We |
| power wash industry. They are coupled in-line and | | | | could pursue this to infinity and never reach a |
| operate on waterpower. The water velocity is | | | | consensus. |