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How to Use Downstream Injectors

Downstream injectors are a very useful tool to have for applying soaps, detergents and acidic solutions. They allow the operator to apply detergent with a power washer which can be a very fast and effective way to get a cleaning solution to the surface saving the operator considerable time. And we all know that time is an extremely valuable asset.

There are many cleaning solutions that require the use of a downstream injector because the solution is too corrosive for the pressure pump and or other components on the power washer. Since the downstream injector can be inserted on the pressure side of the pump after those components it allows the chemicals to be used without damage.

Another feature of using a downstream injector is that unlike upstream injection, the pump does not have to work under a vacuum to draw detergent. This puts less stress on the packing of the pump meaning it will last longer before it will need to be replaced.

The best place to install the downstream injector is to attach quick couplers to both ends and insert it where the pressure hose connects to the power washer. If you are using a hot water power washer then insert the injector where the water exits the burner or the hose reel. The rule of thumb is to insert it at the entry point of the pressure hose. This prevents all the components of the pressure washer from the harsh effects of aggressive chemicals.

A down stream injector works by Venturi effect. Simply put this means that the water from the pressure washer is pushed into a constricted section in the injector. As a result the increased velocity of fluid creates a vacuum, drawing in the solution. There is still pressure prior to the injector but there is a significant drop in pressure after it. Using a low pressure nozzle at the wand will normally allow the down stream injector to work correctly.

Three things will cause the injector to stop working. One is the use of a high pressure nozzle. The benefit of this is that it allows the operator to switch nozzles from low pressure applying detergent to high pressure for rinse. Many find this to be a huge benefit of using a down stream injector because they don’t have to constantly keep returning to the power washer to turn off the soap. Second is using too much pressure hose. The more pressure hose the more resistance there is to push the water through the hose. This creates back pressure and reduces the velocity of the fluid through the constricted area in the injector. So typically the injector will work up to about one hundred and fifty feet of pressure hose before it stops drawing chemical. And finally, gravity will impact the injector. As the low pressure nozzle gets higher than the down stream injector the back pressure increases until it reaches the point that it will no longer draw chemical. This usually begins to happen at distances of ten feet and higher, and can be less based on the length of pressure hose.

This article was published in our weekly addition of Spray Tips™ from if you would like to receive future newsletters please click on this link: Spray Tips

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