When you’re trying to decide on what pressure washer is best for cleaning your fleet, there are several factors you need to consider. You need to understand its volume (GPM), pressure level (PSI), whether to pick downstream or upstream chemical injectors, nozzle types, and of course, what chemicals you plan to use. 

All of these play an important role in ensuring you have a more efficient fleet washing process and can achieve the lowest-cost-per wash

But aggressive cleaners can cause increased corrosion and wear & tear on your pressure washer pump. Because of this, there are two ways to add detergents to your wash. In this article, we’ll break down everything you need to understand about chemical injectors and which one you should use.


Understanding Water Pressure (PSI)

Water pressure is measured in pounds per square inch or PSI delivered to the surface of what you are cleaning. PSI is dictated by the specifications of the pressure washer pump you are using and the nozzle size utilized.

A high PSI is important to break the bond between dirt or grime and the surface. Some bonds are much more difficult to break than others and a higher PSI assists in removing greases, oils, hardened concrete, and asphalt/tar.

That said, most applications rarely need more than 3,000 PSI. Today, most wash professionals are opting for units or nozzle sizes with 2,000-3,000 PSI for safer removal of road film with less risk of damaging paint or decals. This is because the bond of the dirt and grime being cleaned can be broken from most surfaces fairly easily using “bond breaking” touchless soaps.


Why is Water Volume (GPM) Important?

Water volume is actually more important than pressure when it comes to cleaning trucks. Volume refers to the amount of water being applied to the surface being cleaned and is often called “flow rate.” Water volume is measured in Gallons per Minute or GPM.

The GPM of the washer is critical to the time it takes to clean a surface, more volume allows you to quickly remove debris and dirt. With a sufficient PSI for bond breaking, a washer with a higher GPM will take far less time to clean than a lower GPM unit. And time is money!

For an efficient cleaning process, we suggest using pressure washers between 4 GPM to 5.5 GPM.  This is because of water consumption levels and the amount of detergent being applied when using a chemical injector.

Higher GPM pressure washers between 7 - 8 GPM and up are less common in fleet washing due to water/detergent consumption. To be used efficiently, you must work quickly to keep up with the pace of the higher flow rate.

Lower GPM pressure washers between 2 - 3.5 GPM are also less efficient for high volume fleet washing. This is because the lower flow rate will not allow you to work as quickly when applying detergents and rinsing, causing the user to clean in smaller sections to avoid drying.  

It’s the combination of the right PSI and the right GPM that helps make cleaning easy and efficient  But before you stop there, it is crucial you take into account what type of chemical you are using, the method of chemical injection, and the dilution rate of application.


What is a Downstream Injector?

A downstream injector is used to add chemicals or truck wash soaps to the water AFTER the pump at lower pressure. This effect combines your liquid detergents with the water from the pressure washer pump to spray from your nozzle.

How do they work? Downstream injectors use the Venturi effect to suction water into a constricted section of the high-pressure hose to apply detergents. 

Downstream injectors require a drop in pressure from your spray nozzle to create the Venturi effect. The most common examples are dual-lance wands with the brass soap nozzle or the black quick connect nozzle.

There are other methods of downstream injection that require more specialized equipment and pressure washer accessories. This includes foam cannons, X-Jet injectors, and 2-step gun systems

Downstream injector systems are the most common form of chemical injection with your pressure washer. This is because chemical detergents are NOT drawn through the high-pressure pump (or heating coil if using a hot water pressure washer) which prolongs the life of the pump and reduces corrosion. Most downstream injector systems are also relatively lower cost, easier to operate, and will draw detergents at a stronger dilution rate.


What is an Upstream Injector?

Upstream injectors are used to draw add chemicals or truck wash soaps BEFORE the pump at high pressure. Like downstream injection, this effect also combines your liquid detergents with the water from the pressure washer pump to spray from your nozzle.

How do they work? Upstream injectors also use the Venturi effect to suction water into a constricted section of the high-pressure hose to apply detergents.  

Upstream injectors have a different design than downstream injectors which will somewhat restrict the flow of water entering the high-pressure pump to create the Venturi effect.

Upstream injectors do NOT require a drop in pressure with low-pressure soap nozzles. However, they would require a shut-off valve to prevent the draw of chemical detergents when rinsing.  

If you use a freshwater supply tank, you will need a specialized pressure bypass system or use your shut-off valve when releasing the trigger to prevent chemical detergents from returning to your fresh water supply tank.

Upstream injection will produce higher pressure detergent application which improves cleaning performance and can reduce overall detergent consumption.  When using upstream injection, it is best to use milder detergents and low pH presoaks to reduce the corrosion of the high-pressure pump components (and heating coil if using a hot water pressure washer).


About Hydro-Chem Systems

Hydro-Chem Systems is a leading supplier of fleet and industrial truck cleaning solutions. For more than 50 years, we’ve dedicated ourselves to helping private fleet owners, municipalities, schools, farms, manufacturers, and mobile washers across the USA & Canada achieve the lowest cost per wash. To find more information on how you can clean more vehicles in less time, call 616-531-6420 or email us at info@hcsclean.com