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Upstream Injectors Save Time and Use Less Soap

Often applying soaps at high pressure is the most effective way to clean a surface. However, most pressure washers are not equipped to apply soap with upstream injectors.  This reduces the cleaning effectiveness and requires the use of higher amounts of soaps or stronger, more aggressive soaps.

It is important to understand that there are three primary components that make the cleaning process possible: agitation, chemical, and/or temperature.  Agitation can be achieved by applying the blasting power of a pressure washer, brushing, media blasting, etc.  Chemical blends are used to break bonds and attract pollutants away from the surface.  Temperature is used to enhance the cleaning process so as the temperature increases the less time it will take for the cleaning process to transpire.  Depending on what is being removed, the cleaning technician must decide what combination of agitation, chemical, and temperature will achieve the desired results in the most cost-effective and efficient manner.

High pressure soap applications (upstream injectors) are best used when the surface to be cleaned could easily be damaged by more aggressive cleaning detergents or when the use of strong chemicals will have a negative impact from repeated use.  That said, most pressure washing pump components will be damaged if stronger blends of chemicals are run through them, so it is very important to know what will be running through your pump and what effect it will have.

Back in 1982, when I started in the industry, almost every machine was set up with the option of “upstream injection”.  That is because the mass production of pressure washers was not in full swing yet and only contractor cleaners or industrial users had one.  Normally, they were equipped with hot water and upstream injectors.  As time passed many new outlets have entered the market offering equipment targeted more at the general public, who prefers a simpler process for applying soap.  Hence the need to apply soaps with a downstream injector.  It is easy and requires very little knowledge to do it.  For most box store pressure washers, changing out the nozzle to a low-pressure nozzle, AKA a “soap” nozzle, is all it takes to be able to use the pressure washer to apply soap.


To apply soap at high pressure, the soap must travel through the pump.  This is where the term “upstream” comes from, because the soap enters the flow of water as it flows to the pump.  This method works best when a holding tank is use for drawing water into the pump.  By restricting the flow of water to the pump a vacuum can be created because the pump is working to pull water in faster than the flow that can be achieved with just the force of gravity.  Since the restriction is not always the same, a gate valve is used to adjust to the desired restriction.  Next install a metering valve somewhere in the line between the gate valve and the pump.  This is where the vacuum will be created to draw in the soap.  From the metering valve run a hose to the soap tank.

I am Michael Hinderliter, president of  If you found this information useful and educational, please share it with others.   Thank you and have a successful day.

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