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Pressure Washers - how do I choose?

Pressure washers come in all shapes and sizes, so choosing the one that's right for your needs can sometimes be confusing. By asking yourself the few simple questions that follow, you'll go a long way towards ensuring that you choose the right machine for your requirements.

Q1. Will I use the machine for more or less than one hundred hours per year?

Q2. Do I have a good external water supply from the mains?

Q3. Will I be removing  (a) ordinary, everyday dirt and grime or (b)heavy soilage and grease?

Q4. Do I want  a cold water only machine, or do I need hot water/steam capabilty?

A1. OK, if you're going to use the machine for less than one hundred hours per year - a couple of hours a week, say - you'll be fine with a domestic-class machine. If it's going to be much above this figure, my advice is to opt for a commercial-class machine. Why? Put simply, the build quality of commercial machines is higher. The components are more robust, the pump (the heart of the machine) is much more durable and the whole machine is generally more heavily built.

So, given the above, you ask, "is it worth buying a domestic-class machine at all? Wouldn't I be better off just buying a commercial?" Answer - not at all. Whilst the axiom 'buy the best you can afford' certainly holds true, there's no point wasting money on a machine too powerful or heavy-duty for your needs! Please remember, though, that if you are going to use a pressure washer for commercial purposes, using a domestic machine will invalidate the warranty!

A2. An external water supply is by far the most preferable, although all pressure washers can be supplied by water tanks (as not a lot of people realise!) although this will put a heavier load on the pump. Most domestic supplies will be fine for pressure washers, though if yours is particularly poor you might like to consider a booster pump of some kind. A very quick test is to fill a ten-litre bucket from your tap. Note the time it takes to fill - under a minute is fine for most domestic models.

A3. If the answer to this question is (a), then an ordinary cold water machine will be fine. If it's (b), then you're going to need a machine that lets you add a chemical or detergent into the delivery. Generally this is done via a small feed tube that simply sits in the chemical/detergent bottle (dosing is automatic), or on larger machines by an on-board tank that you top-up as necessary.

A4. Now here's a question! As a rule of thumb, if you're looking for a machine for home use, cold water is fine. If you have special applications to consider, such as steam cleaning in food producing plants or premises where hot water must be used, then a hot water/steam stage machine is your option.

I cannot cover all applications here for this type of machine - it's very much a case of (again) the 'right machine for the job', so always be sure to tell a prospective supplier exactly what the pressure washer is going to be used for, for how many hours a day and for how many days per week. Don’t be tempted to save money by buying a smaller, lower output machine - you will regret it in the long run, believe me!

An important point you may like to consider -  Many people, when telephoning for information, ask this one question - "what pressure does the machine deliver?" - and seem surprised at the reply. The reason? Well, even a small domestic machine will deliver about 1200-1400 p.s.i., whereas the larger commercial machines may only deliver some 1400-1600 p.s.i.. So what's the difference?

Simply put, it's the amount of water used. Imagine. You are stood in front of a huge dam. From the dam wall project two pipes. One is half an inch in diameter, the other a foot. The chap at the controls is just about to open the valves that allow water to run freely through both pipes. You have to stand in front of one - which would you choose? You see, both pipes would be subject to exactly the same water pressure. (If you don't believe me, check a basic primer on hydraulics) but the larger diameter pipe would have a much greater water flow.

If you stood in front of the smaller pipe, you'd be wet and it would be unpleasant. The big one would blow you off your feet! So, if you're looking for a really powerful machine, check the water flow - anything above 500 litres/hr. is getting fairly serious! The following may make it a bit clearer-

PSI and LPM

One quick way to compare pressure washers in general is to multiply the PSI (pounds per square inch) times the LPM (litres per minute) and you obtain a "work" value. For example, for a pressure washer operating at 1500 PSI and 10 LPM, the work value is 15000 (1500 x 10). At 1300 PSI and 16 LPM the work value is 20800 (1300 x 16). It can readily be seen from this that PSI isn't everything!

Flow or LPM affects the time it takes to clean something. The higher the flow, the shorter the length of time it takes to clean - this generally being achieved by having a more powerful (higher rated) motor. Pressure (in PSI) determines the ability of the force of the water needed to break the bond of the material from the surface.

Basic pressure washer care - user guidelines

Water-

1. Before use, always check the inlet filter for dirt or debris. Connect the water supply hose and, without the lance attached, squeeze the trigger to run water through your pressure washer before connecting the power supply. This bleeds the pump and flushes any dirt out - it also reduces the risk of blocking the lance, especially after a long period without use.

2. Unless you are drawing water from an open source such as a water butt, always have at least 25 feet of uncoiled hose between the tap and the machine. When the trigger is released, a shock wave is transmitted up the supply hose where it is absorbed, which is normal. If the supply hose is too short, or coiled, the pulse may not dissipate safely and be transmitted back to the machine, which could cause damage to the pump seals or valves, symptoms of which are the motor 'hunting', low or no pressure and/or water leakage.

3. It is advisable to use a non-return connector valve at the tap end of the water supply. If one is connected to the machine end, it will restrict the pressure when the trigger is released with possible resulting pump damage.

4. After switching off the machine, squeeze the trigger to release any residual pressure. This allows the high pressure hose to be removed easily.

Electrical Supply-

If an electrical extension lead is used, it must be adequate for the amperage drawn over its length. Most pressure washers will draw between 7 and 9 amps, so a lead with 13 amp rating should be the minimum used.  Inadequate extension leads will cause over heating and subsequent damage to the motors as will failing to uncoil the lead - always uncoil it fully. If in any doubt, seek the advice of an electrician or qualified person.

Chemicals-

Use only chemicals recommended by the manufacturer, or those specifically formulated for use through a pressure washer, through your machine. Use of aggressive chemicals could cause significant damage and invalidate the warranty.Always flush machine with fresh water for at least 1 minute to clear any residual chemical - this avoids chemical deposits building up and causing internal damage to the pump.