9/8/2017

How Pressure Washers Work

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If you own a pressure washer, and you use it quite often, the machine is bound to break down sooner rather than later. Most people use a pressure washer without bothering to understand what makes it work. Truth be told, we don't need to know everything about pressure washers in order to use it. But knowing the basics of its inner workings can help you troubleshoot and repair problems before they get out of hand. Performance issues such as sudden pressure drops and loss of water flow are difficult to investigate if you don't know anything about pressure washers.

Once your pressure washer breaks down, you have three options: Buy a new pressure washer, hire a technician, or do the repairs yourself. Buying a new unit is definitely expensive, and getting a technician to do the repairs can end up costing you almost the same amount. Learning to do basic repairs, however, can benefit you in the long run. Once you know how to basic troubleshooting and servicing, you're set for life. Of course, to perform repairs, you must understand how a pressure washer works.

If you already know how to do diagnostics and repairs, you'll find nothing new in this guide. I wrote this article for people who want to learn how pressure washers work. From there, people can then move on to learning how to perform repairs. If you're interested in knowing about the inner workings of pressure washers, then read on.

How Pressure Washers Work

First things first: We need to define what a pressure washer does.

A pressure washer is a machine that boosts the ability of water to do work by adding energy. How does this happen?

Imagine an ordinary garden hose with a nozzle. The garden hose is attached to an outdoor faucet. As you probably know, maximum water flow (let's say 5 GPM) can be achieved if the nozzle is completely open. As the nozzle is closed, the flow rate is restricted until zero flow is achieved. This is what we call a constant pressure system.

Now imagine detaching the nozzle and connecting the garden hose to a pressure washer pump. A motor or engine drives the pressure washer pump at a particular fixed speed. Depending on the engine output, the pump will move a set amount of water, measured in gallons per minute or GPM. The amount of water moved will not change unless the user wills it. We also call this type of pump a fixed displacement pump.

Let us say this hypothetical pump delivers water at 5 GPM. Unlike the previous garden hose setup, the hypothetical pressure washer pump will only deliver 5 GPM even if 10 GPM is available from the faucet spigot. Conversely, the pump will try to draw water at 5 GPM even if the spigot delivers less water than what is required.

Attaching a hose and nozzle to the pump outlet will not alter the flow rate being delivered. The pressure washer pump will continue on drawing and moving water at 5 GPM. However, the hose and nozzle will change the pressure of the water being released. With a small nozzle orifice, the pressure washer pump will have to work extra hard to push the same amount of water through a smaller outlet.

This is what we call a constant flow system, and this principle is what makes pressure washer cleaners possible. The smaller the nozzle orifice, the more the output flow is restricted, and the more power is required from the engine or motor to maintain the constant flow.

In the event of a nozzle blockage, this could quickly turn dangerous. With nowhere to go to, the pressure within the hose will quickly build up. The water still needs to go somewhere. Which is why all modern pressure washer pumps have an inbuilt relief valve to allow for an alternate discharge outlet in case the water cannot be released through the nozzle.

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