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How does a pressure washer work?

A person uses a pressure washer to clean their decking

Everything you need to know about pressure washers, and what makes them so great for tackling dirt and grime

The best pressure washers are the ultimate tools for blasting away dirt, and refreshing everything from patios, block paving and decking, to cars, bikes and more. They’re incredibly versatile and, better yet, they’re incredibly satisfying to use.

If you’ve never used a pressure washer before, but are interested in snapping one up for yourself, we’ve covered everything you’ll need to know, including how they work, what you can do with them and what brands make them. We’ve also included some expert commentary, courtesy of spokespeople from Halfords and Kärcher, to help ensure you’re in safe hands.

How does a pressure washer work?

In essence, a pressure washer is a machine that blasts out a stream of water at a much higher pressure than a normal garden hose – despite being connected to the same regular outdoor tap – letting you easily scour dirt from surfaces in record time.

Pressure washers can generate this power thanks to their cleverly designed internals. Initially, water enters the machine via a hose from the outdoor tap – this water inlet usually has a built-in filter to stop dirt and debris from entering the pressure washer – then, once inside, a pump accelerates the water to high pressure and it exits via a reinforced hose attached to a trigger gun (or other attachment), physically removing dirt by sheer force.

The key here is the nozzle, as this is what delivers the jet of water that makes it great for cleaning, rather than just soaking things like a hose. Most pressure washers have an adjustable nozzle to change the strength of the jet to suit different cleaning tasks – at its strongest, it will blast away dirt; at its gentlest, it’s better for rinsing off detergent suds.

So, a pressure washer only consists of a few key components: a water pump powered by a motor, a reinforced hose and various nozzles or attachments. The hose should be rated for pressure higher than the pump in the pressure washer can reach, but this isn’t likely to be something you need to worry about, as pressure washers generally come with suitable hoses.

As for power, pressure washers either have an electric motor, requiring a power outlet or a petrol-powered engine. Petrol-powered models tend to be more powerful but, unsurprisingly, more expensive. Some electric pressure washers may be battery-powered for mobile cleaning – particularly convenient if you want the portability but not the expense or bulk of a petrol-powered model, or if you don’t have ready access to an electrical outlet.

Jamie Louram, a buyer at Halfords, states that “a portable or cordless pressure washer, like the Karcher OC3 Portable Cleaner, is the perfect choice for on-the-go cleaning such as rinsing off your bike, wellies, dog or pushchair at the end of a muddy day. You can easily store it in your car boot and take it with you on a camping trip or long walk.”

Certainly, the ability to wield such substantial cleaning power regardless of where you are can be rather liberating, so long as you’ve got a suitable water source – even just a large bucket – to make it work.

Many pressure washers also allow you to insert detergent into the water loop – either by physically slotting a bottle of detergent directly into a purpose-built inlet on the machine, or via a small hose inserted into the bottle.

Lastly, while most pressure washers come with a trigger gun as standard, which sprays water when a handle is depressed, there are various attachments you can buy to help tackle specific cleaning tasks. For example, you can get patio cleaning attachments, which allow you to clean larger areas thanks to rotating nozzles powered by the jet of water itself.

Choosing the right attachments and detergents will vary, depending on your needs. Louram recommends considering various cleaning products for cars, outdoor furniture and surface types, though checking their suitability directly with the manufacturer is, as always, best.

A person uses a pressure washer to clean their car

“If you need to clean a large area, invest in a Karcher T5 Surface Patio Cleaner, if it will fit your specific machine,” Louram suggests. He goes on to recommend that “you can also use the Karcher WB7 Plus Wash Brush & Foamer to suit many different cleaning challenges as the brush shape is optimised for maximum reachability, and the variable pressure capabilities allow for cleaning of cars, motorbikes, caravans and other external surfaces around the home.”

READ NEXT: Best Kärcher pressure washers we’ve tested

What can you do with a pressure washer?

“Pressure washers are a cleaning tool loved by many, yet the wide capabilities of the pressure washers can sometimes be missed,” says Harry Turner, product manager for pressure washers at Kärcher.

While most people use pressure washers to clean their driveways, patios and decking, you can also put them to work rejuvenating cars, sheds, fences and all sorts of other outdoor surfaces. However, it’s important to ensure you’re using the appropriate level of pressure and the right tools to avoid damaging anything.

“For washing cars, opt for a gentle spray setting to avoid damaging delicate paintwork, while for driveways, a more powerful setting may be necessary to tackle stubborn stains effectively”, Turner continues. “Additionally, always maintain a safe distance from the surface being cleaned to prevent accidental damage.”

It’s always best to start on a lower setting, if possible, and test a small part of a surface to check that you’re using an acceptable level of power. According to Louram, “A pressure washer can also make light work of clearing out mould and small weeds that grow between patio bricks, but be careful not to clear out the soil or sand in between, and limit the number of cleans to once a year to minimise any wear and tear regular use could cause.”

When it comes to pressure washing fences and decking, Louram also states that you should “be sure not to place the head too close or you can risk stripping the paint. After a few uses, you may begin to see the paint start to come off so, if needed, it can be a good idea to repaint, stain or seal the fence if this is the case. If you are planning to repaint the fence anyway, a pressure washer is a great way to clean it beforehand”.

A woman cleans her garden furniture with a pressure washer

You can also spruce up your patio furniture with a pressure washer, so long as it’s hardy enough to withstand the power – older rattan furniture might not be up to it, and even some plastic chairs might be too fragile. As with most things, it’s worth checking with the manufacturer to see if your furniture is suitable for pressure washing. If it is, you’ll be amazed at the difference a quick blast of water can make.

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Who makes pressure washers?

As the global market for pressure washers only continues to grow, many manufacturers currently make pressure washers, with some of the most highly regarded being made by instantly recognisable brands like Kärcher, Bosch and Ryobi. But there are also excellent affordable options from other brands like Halfords, Worx and Nilfisk.

You can see some of our top picks in our roundup of the best pressure washers.

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