Soft Washing is a term which describes a modern, more advanced cleaning process under the “power washing” umbrella; specifically, soft washing is a process for cleaning which uses chemical solutions as its source of cleaning power (instead of mechanical agitation through high pressure) to clean surfaces. There are a couple ways that soft washing can be accomplished, and the method utilized is highly dependent upon the application. Whatever system is used, the addition of chemical cleaners has forever changed what is possible through power washing services.

Downstream Injection: The Secret to Unlocking a Pressure Washer’s Potential

Downstream injection is the process of introducing a concentrated chemical solution into the water flowing through a pressure washing system. This is achieved by installing a chemical injector device downstream of the pump (beyond the pump’s discharge port). However, simply adding a chemical injector is not sufficient; the entire pressure washing process must be adjusted to account for this setup.

Downstream chemical injectors operate based on the Venturi principle. When fluid flows from an area with a larger cross-sectional diameter to one with a smaller diameter, the fluid velocity increases, while the pressure in the smaller cross-sectional area decreases. This pressure differential enables the downstream injector to draw in a concentrated cleaning solution through a secondary inlet port on the injector.

The mix ratio of the cleaning solution depends on several factors: the injector’s design, the size of the orifice within the injector, the flow rate of the system, and the pressure drop across the injector (regulated by its internal orifice); generally, though, the mix ratio is close to 1:5. For systems with very high flow rates (over 5 GPM), these injectors struggle to draw in enough of the chemical solution to maintain an effective final ratio, working against the idea that “more is always better.” Furthermore, for services like roof washing (where very high chemical concentrations are needed), a downstream injection setup will be insufficient, and a different pump system (typically a diaphragm pump) must be used.

Combine Downstream Injection with a J-rod: The Key to Soft Washing Efficiency

Combining a downstream injector with a multi-nozzle device, such as a J-rod, adds more functionality by using system pressure as an on/off switch for the chemical injector. When system pressure drops below a specific threshold, the chemical injector’s inlet valve opens, drawing the cleaning solution into the water flow. When the pressure rises above this threshold, the inlet valve closes, stopping the chemical solution's flow. This setup allows the operator to easily switch between applying the cleaning solution and rinsing. This is the “two-step process” that is often advertised for soft washing services. Careful selection of nozzles can substantially increase soft washing efficiency and effectiveness.

Turbulence: The Mixing Agent of Downstream Injection

Downstream injection, by itself, does not fully mix the cleaning solution with water. The solution mixes gradually as it travels through hoses and fittings, but uneven distribution in the flow can create corrosion hotspots, leading to premature wear on system components. For cleaning solutions containing bleach, this is especially challenging.

To mitigate this, deliberate turbulence can be introduced into the flow path. For example, adding a stainless steel, high-pressure-rated 90-degree elbow after the injector creates localized turbulence, promoting better mixing while concentrating corrosion in a single, easily replaceable fitting. This targeted wear management reduces the overall cost of maintenance.

Unlike systems that use centrifugal pumps (where restrictions reduce flow rate), pressure washing systems with positive displacement pumps (PDPs) maintain a consistent flow rate despite added restrictions. The pressure drop caused by such components acts like a voltage drop in an electrical circuit, spreading the "load" across the system. A well-designed pressure washing system accounts for this, ensuring sufficient pressure remains at the nozzle to achieve optimal cleaning.

The Surface Work Difference

At Surface Work, we take the guesswork out of power washing. Through research, experience, and commitment to excellence Surface Work ensures consistent, top-tier results for every project. Through years of refinement, Surface Work has developed a proven system that delivers outstanding cleaning results without the hassle.

From Strawbridge to Alanton, we’ve completed hundreds of house washing services in Virginia Beach. Chances are that your neighbors already trust Surface Work for their power washing needs. Let us show you the difference a professional touch makes—contact Surface Work today!