Petrol or diesel pressure washer buying guide

Petrol or diesel pressure washer buying guide

Jeremy, Construction site supervisor, Cardiff

Guide written by:

Jeremy, Construction site supervisor, Cardiff

If you're looking to power clean professional equipment, walls or other surfaces on a regular basis, nothing beats a petrol or diesel pressure washer. These pressure washers can work with hot water or cold and a range of accessories for high power cleaning on the move. Read on to find the right pressure washer for you.

Important features

  • Pressure
  • Flow rate
  • Engine type
  • Power
  • Accessories
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Choosing a petrol or diesel pressure washer to suit your needs

The main characteristics to consider are:

  • Water temperature: either just cold water, or hot and cold water;

  • Pressure (from approx. 140 to 280 bars): the higher the pressure, the easier your job will be;

  • Flow rate (between 400 and 1000 l/h): the higher the value, the more efficient the pressure washer will be;

  • Power: not the most important characteristic, but related to the two previous criteria. The key point to remember is that the higher the power (hp) and engine capacity (cc), the less strain this puts on the engine to achieve equivalent pressure and flow rate;

  • Engine type: again, not the most important characteristic, but related to the previous criteria and to fuel consumption (for heavy use, a diesel engine is better).

When choosing a pressure washer, you'll need to figure out what you want to do with it and how often you will use it.

  • For intensive use and/or for cleaning large or very dirty surfaces, you should look for a diesel-powered hot water pressure washer with a pressure rating of 220 bars and a flow rate of at least 600 l/h.

  • Professionals looking for a pressure washer for daily use should choose one with a diesel engine, a high flow rate (600 l/h) and a high pressure rating (200 bars).

  • For users who intend to use their pressure washer regularly, but not daily, a pressure washer with a petrol engine, 150 bars of pressure and a flow rate of 500 l/h will do the job.

It's worth noting that pressure washers usually come with various accessories (nozzles, telescopic lances, floor brushes, etc.), but you can always buy more later on.

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Accessories

Fuel-powered or electric pressure washer

Petrol and diesel vs. electric pressure washers

Petrol or diesel-powered pressure washers are ideal for intensivecleaning of professional equipment, agricultural and industrial machinery and external walls and floors. With the exception of some professional models (Kranzle, Nilfisk, Honda, etc.), electric pressure washers are more fragile than their petrol or diesel counterparts and can be damaged by overheating. Moreover, in terms of general performance, petrol and diesel models are superior. If you're looking for a robust pressure washer for your building site or farm, or for industrial use, then you definitely need a petrol or diesel model.

Petrol and diesel pressure washers are more powerful than electric models and offer the following characteristics:

  • Flow rate of up to 1,000 l/h (litres per hour) compared to a maximum of 600 l/h for an electric pressure washer;

  • A pressure rating of up to 280 bars (whereas electric pressure washers only reach 160 bars);

  • Hot or cold water, whereas the majority of electric models can only be used with cold water.

On the other hand, petrol and diesel engines both require regular maintenance (oil, spark plugs, draining, air filter). They are also heavier and noisier and emit more greenhouse gases.

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Electric pressure washers

Flow rate, pressure and power ratings

As is often the case, you can't have it all. The basic law of hydraulics means that, for any given diameter, the higher the water pressure, the lower the flow rate (and vice versa).

It is the pump of a pressure washer which propels the water, i.e. which determines the quantity (the flow rate) and force with which the water is expelled (the pressure). These two parameters are therefore affected by the diameter and length of the hose and the size and type of nozzles you use.

Choosing a pressure rating for your pressure washer

Pressure is measured inbars. A bar is a measurement of weight (in decanewtons, daN) per surface area (in cm2), where 1 bar = 1 daN/cm2.

The higher the pressure, the quicker the pressure washer will remove marks and dirt (mud, foam, etc.). When making your choice, you therefore need to think about what types of dirt you want to clean and how often you want to use your pressure washer.The pressure ratings of petrol and diesel pressure washers range from 120 bars to over 270 bars. Use the following values as a guide:

  • 120 to 150 bars is sufficient for cleaning your car or patio;

  • 150 to 190 bars will efficiently clean outdoor walls, and patios larger than 50 m², etc.;

  • 190 to 230 bars is what you need to clean agricultural, industrial or construction machinery;

  • 230 bars or higher will ensure even more efficient cleaning of patios, outdoor walls and agricultural or industrial machinery.

Flow rate: a measure of efficiency

Flow rate is the quantity of water expelled in a given time. It is expressed as a number of litres per hour (l/h).

Along with pressure, the flow rate determines how long it will take to clean a surface: the higher it is, the quicker and easier your job will be, as you won't need to go over the same area as many times.

Petrol and diesel pressure washers usually have a flow rate of between 400 and 600 l/h, although top-of-the range models can reach over 1,000 l/h.

Engine type: petrol or diesel?

4-stroke engines 

This kind of technology is only found with medium engine capacities (130 to 250 cm3).

The engine runs on petrol, has an oil sump and a filter, and is air-cooled. Regularmaintenance is essential.

Given the low compression ratio, a manual starter can be used.

This type of engine is quieter and also less complex than a diesel engine, and is generally used for pressure washers with medium power ratings.

Some models feature a hot water function.

Diesel engines

Diesel engines are used for heavy-duty pressure washers.

Diesel engines are complex pieces of machinery which require special care and regular maintenance (checking levels, battery, spark plugs, filters, etc.)

They usually have an electric starter.

Pressure washers with diesel engines are relatively heavy and loud and are intended for outdoor use (unless you choose a model with an acoustic enclosure).

Diesel pressure washers often offer the option to heat the cleaning water and many have a built-in detergent tank or dispenser.

Given the cost (both to buy and maintain), size and weight of these models, they are primarily designed for professional use in an agricultural or industrial setting.

Power: horsepower or watts

The power rating of pressure washers is indicated in metric horsepower (hp) or watts (W).

The conversion ratio is 1 hp = 735 W.

The power of a petrol or diesel engine is usually given in horsepower, although some manufacturers state the value in watts (W). In this case you can easily convert the figure to horsepower.

Power is not directly related to the output pressure or the flow rate, but it does influence these values. It all depends on the type of mechanism, drive and technology used, the manufacturing quality, etc.

In other words, power isn't the most important characteristic when it comes to choosing a pressure washer.

That said, if you are considering two models with similar pressure ratings and flow rates, go for the more powerful one, because it will achieve the same results while putting less strain on the engine, thus extending the service life of the equipment.

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Pressure washers

Hot water pressure washers: the benefits of hot water for cleaning

If you've ever tried doing the washing up in cold water instead of hot, you'll have noticed that the water temperature affects how quickly and how well you do the job.Hot water is much better at removing and dissolving grease and stains than cold water. In concrete terms, that means more efficient and quicker cleaning, lower water consumption and, in the end, less work for you! However, hot water can damage some surfaces (tiled floors should only be cleaned with cold or lukewarm water for example), so it is best to check beforehand, or start by doing a test on a small area.Things to check before purchase:

  • Maximum water temperature the surface can withstand;

  • Maximum temperature of the water jet.

Accessories for petrol and diesel pressure washers

Power, pressure and flow rate are the key factors which determine how well a pressure washer does its job, but there are many other features, components and accessories which can make cleaning easier and safer. These include:

  • Reduced sound level (dB);

  • An electric starter as opposed to a manual starter;

  • A thermal safety valve to protect the generator if left running while not in use (if the temperature gets too high, the water is discharged);

  • An oil-level safety switch;

  • A brass pump (stronger);

  • The tank volume;

  • A strong, reinforced frame with a folding handle;

  • Air-filled wheels for better handling on bumpy surfaces;

  • A direct detergent injection system with a regulator;

  • A pump which can draw water (to clean using water from a pond or lake, for example);

  • A cage structure with attachment points for loading via crane (optional);

  • A suction pump to draw detergent;

  • A hose reel and compartments for storing other accessories.

Main accessories for petrol and diesel pressure washers

You can find all kinds of pressure washer accessories to help you with specific jobs.

Accessories

Use

Type of water

Straight jet nozzle

General cleaning

Unblocking

Removing dirt

Cold water

Hot water

Rotary nozzle

Removing dirt from floors/walls

Light stripping

Cleaning concrete

Cold water

Hot water

Spray nozzle

Light cleaning

Spraying various products (degreasing agents, weed killers, etc.)

Cold water

Detergent tank/dispenser

Car washing brush

Cleaning car bodywork

Cleaning wheels/rims

Cold water

Hot water

Detergent tank/dispenser

Floor/wall brush

Cleaning walls/floors (rendered walls, patios, tiled floors, concrete, waxed concrete, etc.)

Cold water

Extension hose

Working at height (roofs, gutters, scaffolding, etc.)

Cold water

Hot water

Extension lance

Cleaning floors (with a floor brush for example)

Cleaning tall vehicles (trucks, tractors, etc.)

Cold water

Hot water

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Pressure washer accessories

Tips for using and cleaning petrol/diesel pressure washers

How to clean a petrol or diesel pressure washer

To keep your pressure washer in good working order, it's important to clean it regularly.

  • Clean the air filter (can become clogged depending on where you use your pressure washer – check regularly).

  • Clean the spark plug (and replace when necessary).

  • Check the oil level (gauge) and top up when required.

  • Drain the engine oil after the specified number of hours of use (refer to the manual).

  • Keep the frame and wheels clean.

  • Descale the pressure washer (how often you need to do this will depend on how hard your water is) and clean the filters.

  • Make sure that all the screws are tight (sometimes vibrations can cause screws to come loose).

Tips for using a petrol or diesel pressure washer

  • Take breaks to prevent the pressure washer from overheating.

  • Wear hearing protection.

  • Always run the pressure washer until the fuel tank is completely empty (otherwise the poorly filtered fuel residue may clog up the carburetor).

  • Store the pressure washer in a dry place.

  • Empty the hose and lance, and disconnect if the pressure washer is exposed to negative temperatures (while in storage, for example).

 
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Guide written by:

Jeremy, Construction site supervisor, Cardiff

Jeremy, Construction site supervisor, Cardiff

Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres, I have been able to coordinate, audit and organise all sorts of construction sites. For 4 years now, I am restoring and building an extension to a bungalow in the heart of the Welsh countryside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electrics, anything goes! My wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions and advise you on choosing your tools? Easy!

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