There is always some confusion when learning about how to apply chem when power washing. You hear everyone talk about downstream…and then you hear everyone talking about 12v, booster pump, air diaphragm. It can be overwhelming. Let us break it down in a simple, easy to understand format.

Be sure to check out our post on how to build your proportioner here: Wash Life Mixer List

What is it?

Downstream is a way to apply chemicals using a pressure washer. A downstream injector is installed after the pump. There is a nipple, where a soap line is connected. The soap line has a small strainer to keep out debris. Guys typically take a 5-gallon bucket, fill it with SH and surfactant of choice, and drop the strainer into the bucket. When you use your soap tips (commonly known as the black tip, professionals use a J-ROD) the injector will pull chemicals from the 5-gallon bucket as you spray water (remember the injector will only pull when you spray with a “soap” tip!). The ratio in which the injector pulls chemicals will vary from setup to setup. 

Factors that Affect Ratio

Factors that cause the injector ratio to be different for everyone include the type of injector being used (orifice size)! Length of high-pressure hose on the reel (too long may cause injector to pull less), what size tips you are using to apply soap (are they big enough), etc.

For example: A 4gpm machine with 200ft of hose, should be using an injector rated for a 2-3gpm machine. The orifice will be larger, allowing injector to pull more chem. If you get an injector rated for a 4gpm machine with that much hose – you will be lucky to pull any chem. I highly suggest calling a trusted vendor when placing your order. Tell your vendor about your setup, ask them for exactly what you need. They know exactly what parts to get you to match the setup you have. I prefer to use Russ Johnson over at Southside Equipment.

To better understand application strength with a downstream injector, I am going to give another example. We are going to do an example with some basic numbers so the math is easy to understand.

Real Life Example

Say the injector is pulling at a 10:1 ratio. This means for every 10 gallons of water sprayed with the power washer, the injector will suck up 1 gallon of chemicals from the 5-gallon bucket. Let us say the strongest SH you can find in your area is only 10% strength. This means when you fill your 5-gallon bucket up with straight SH (not cutting it with any water!), the highest strength application you are able to apply would be a 1.0% strength application. If you fill your bucket up with “50/50” meaning half water/half SH, then the application strength will only be 0.5%. Make sense? Good.

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