Understanding the Venturi Effect in Chemical Injectors: How Switching Between High and Low-Pressure Lances Controls Chemical Flow

Chemical injectors are essential tools for professional high-pressure cleaning, allowing you to seamlessly apply cleaning chemicals during your wash. There are several types of chemical injectors, each functioning differently depending on the system. For example, premium Ehrle models, like the Ehrle HD and Ehrle KD series, incorporate dosing and injection systems to mix chemicals with water for maximum cleaning efficiency.

In contrast, injectors such as the ST160 that we frequently fit to Nailsea engine-driven pressure washers (such as the Honda Driven or WF Range) don’t use active dosing or injection. Instead, they rely on a fascinating principle of fluid dynamics known as the Venturi effect. If you're unfamiliar with the Venturi effect, the inner workings of these injectors might seem like a bit of a mystery. And indeed, there is an element of intrigue since you don't physically adjust a dial or flip a switch to control the chemical flow.

So how does this work? The key lies in simply changing your lance setting. When you switch from a high-pressure to a low-pressure setting, the pressure washer "knows" it’s time to start or stop applying the chemical. But what’s happening behind the scenes? How does this simple, manual adjustment signal the change?

In this article, we'll dive into the mechanics of the Venturi effect and how it powers these chemical injectors, demystifying the process for both professional cleaners and those curious about how their equipment operates.

What is the Venturi Effect?

The Venturi effect describes how the speed and pressure of a fluid change as it flows through a narrow section of a pipe. When water flows through a constriction, the fluid must speed up, and as it does, the pressure in the narrow section drops. This drop in pressure creates a vacuum effect, which can be harnessed to draw chemicals into the water flow without the need for an additional pump.

In a chemical injector, this principle is used to pull cleaning chemicals into the water stream, allowing them to mix before being sprayed out through the lance.

How Chemical Injectors Work with the Venturi Effect

A chemical injector is installed along the flow of water between the pump and the lance. Inside the injector, the water passes through a Venturi tube. This tube has a narrow section that speeds up the water flow and creates a pressure drop. This low-pressure zone then draws chemicals into the water flow from an attached chemical supply.

However, the injector’s ability to draw chemicals depends on the pressure of the water. This is where high-pressure and low-pressure lances or adjustable/vario lances come into play.

Switching Between High-Pressure and Low-Pressure Lances

Many high-pressure cleaning systems come with two types of lances:

• High-pressure lance: Used for intense cleaning with water alone.
• Low-pressure lance: Used to mix and spray chemicals when needed.

High-Pressure Lance: No Chemical Injection

When using a high-pressure lance, the water is forced through the system at maximum speed and pressure. While this is excellent for cleaning tough dirt and grime, it does not allow the chemical injector to work. Here’s why:

• The high-pressure water maintains relatively equal pressure throughout the system. This consistent pressure is later used, in a similar way to the Venturi effect, to convert pressure into velocity for effective cleaning. However, without a significant pressure difference, the Venturi effect cannot occur sufficiently enough in the injector, meaning no vacuum is created to draw chemicals into the water.
• In high-pressure mode, the injector effectively turns off, and only water is sprayed.

Low-Pressure Lance: Chemical Injection Activated

When you switch to a low-pressure lance, the flow of water is effectively increased through the system reducing in a lower pressure. As a result:

• The pressure difference inside the narrowing tube of the chemical injector becomes low enough to trigger the Venturi effect, creating a vacuum that pulls the chemical into the water stream.
• In this mode, the chemicals mix with the water and are sprayed at a lower pressure, perfect for applying detergents or cleaning solutions.

Using Adjustable/Vario Lances for Chemical Injection Control

Many high-pressure cleaning systems feature adjustable or vario lances, allowing you to change pressure settings without the need to swap lances. These lances offer the convenience of both high and low pressure in one tool by simply twisting or adjusting the nozzle. This adjustable mechanism works similarly to switching between separate high- and low-pressure lances but requires only a quick adjustment at the nozzle. Typically, this involves twisting or pulling the nozzle protector to widen or narrow the nozzle’s orifice, thereby changing the pressure.

How Adjustable Lances Work

• High-pressure setting: When set to high pressure, the nozzle creates a strong, concentrated stream of water. This does not allow for chemical injection because the Venturi effect is not strong enough to pull the chemicals into the water.
• Low-pressure setting: When adjusted to low pressure, the nozzle allows water to flow more slowly, reducing the pressure. This reduction activates the Venturi effect, and the chemical injector begins to draw the cleaning solution into the water stream.

Why The Venturi Effect Matters for Your Cleaning System

Understanding the role of the Venturi effect and how switching between high-pressure and low-pressure settings activates or deactivates the chemical injector allows for:

• Greater Control: You can control when and how much cleaning solution is mixed with water by adjusting the lance or switching between high- and low-pressure modes.
• Efficiency: The ability to use chemicals only when necessary and switch back to high-pressure water alone means that less cleaning solution is wasted, reducing both cost and environmental impact.
• Versatility: With adjustable lances or a dual-lance system, operators can switch quickly between applying chemicals for deep cleaning and using high-pressure water for rinsing, without needing to stop and manually add detergents.

Conclusion

The Venturi effect is a simple yet powerful principle that enables chemical injectors to function in high-pressure cleaning systems. By understanding how this effect works and how to switch between high-pressure and low-pressure lances or use adjustable/vario lances, you can maximise the efficiency and effectiveness of your cleaning equipment. Whether you’re using it for commercial cleaning, agricultural applications, or industrial settings, mastering this technique ensures optimal results every time.