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