Pressure Washer Buying Guide
Pressure washers are a relatively new tool. Over the last ten years the quality has increased as prices have become more
affordable. The cleaning ability of a pressure washer is great, removing dirt, grime and algae efficiently and effectively. Some may
consider this item a luxury purchase, but a pressure washer can greatly increase the ability to maintain and clean your property,
giving it greater value. The goal of this buying guide is to help you understand what a pressure washer does and what you need to
look for when deciding to purchase one for yourself.
Before we start talking about buying pressure washers we need to define some basic ratings
HP (Horse Power) - How much power the engine can generate. This rating is important because it directly relates to how much
pressure the pump can generate.
PSI (Pounds Per Square Inch) - How much force is being generated and released by the pump.
GPM (Gallons Per Minute) - This is the rating given to express how much water is being consumed and released by the machine.
CPU (Cleaning Power Units) - This is one of the least understood, yet most important rating for pressure washers. To determine the
CPU rating of a pressure washer, you multiply the PSI by the GPM. The greater the CPU the greater the ability the machine has for
cleaning deeply and effectively. Often a consumer is so focused on the PSI of the machine that they do not take the time to look at
the CPU. For example, a pressure washer may have 2800 PSI and 2 GPM giving it a CPU of 5600. Another pressure washer has only
2400 PSI but has 3 GPM giving it a CPU of 7200. In this example the lower PSI machine has more than 20% greater cleaning power
than the higher PSI rated machine. The result is that the 2400 PSI machine will be able to clean an area 20% faster than the 2800 PSI
machine. CPU is sometimes called Cleaning Unit (CU) or Cleaning Power(CP). The CPU rating allows the consumer to compare
different machines effectively.
Now consider this, a garden hose will be about 6 GPM and 10 PSI giving it 60 CPU. With a standard spray nozzle attached to the
garden hose you can get around 5 GPM at about 40 PSI generating 200 CPU. We all have seen the difference of how much more
effective a simple spray nozzle is at cleaning dirt off of surfaces. Trying to clean your driveway with your garden hose spray nozzle
generating 200CPU is fairly ineffective. However, if we take a midrange pressure washer a 2 GPM and 2500 PSI (5000 CPU) this is a
staggering 25 times increases over a spray nozzle. A commercial pressure washer at 4GPM and 4000 PSI is an incredible 16000 CPU.
It is not difficult to imagine the difference in efficiency.
Components of the Pressure washer.
Every pressure washer is made up for four main parts. It is important to have an understanding of the components and what they
do.
Pumps
This is the part of the pressure washer that receives water from your garden hose, pressurizes the water to thousands of PSI then
sends it out. There are several common types of pumps that you will see in commercial and home owner type machines.
The wobble pump is on the low end of quality. The basic design consists of a plate that is offset and then forced to wobble by
several pistons pushing against it. There are two or more pistons pushing against a plate at different intervals which makes it the
plate "wobble" very quickly, creating pressure. This style is very inefficient (70% due to piston spring resistance on each stroke).
The axial pump is very similar in design, but has a larger oil reservoir and larger bearings. This allows the pump to run cooler and
results in longer pump life. The larger cylinders in the axial pump allows it to generate more PSI and GPM than a standard wobble
pump. Axial pump performance is an improvement over the wobbles pump, but still suffers from piston spring resistance.
The triplex pump is a piston and plunger design featuring three piston rods that are synchronized together creating a smoother
pressurization resulting in more consistent flow that nearly eliminates pulsation. These are often on much higher quality machines.
A triplex pump is much more efficient than an axial-style pump. Triplex pumps also run much cooler and lasts longer. Another
benefit of this design is that a Triplex pump generates much less heat and therefore runs cooler than an axial-style pump. Heat is
the number one cause of failure in high-pressure pumps. For this reason, an axial pumps can easily provide 1,000 hours or more of
operation before needing any maintenance, whereas a wobble or axial-style pump typically has a life span of 200-600 hours, after
which the pump cannot be repaired economically. When a camshaft pump does require maintenance, the easily accessible pump
head, replaceable cartridge-type valves, and ceramic piston sleeves makes repairs quick and easy.
Drive System
The "drive" describes how the motor is connected to the pump.
Direct drive systems are the most common. Compared to a belt drive system this is a much simpler method needing less parts and
space resulting in a more compact design. Direct drive is also considerably more economical than an equivalent rated belt drive
machine.
Belt drive systems are typically seen on more industrial platforms. The belt drive turns at a much lower rpm (1725rpm vs 3450rpm
of a direct drive). The belt absorbs engine vibration which will wear out a pump faster. Since the pump turns at a slower speed all
the pistons and valves in the pump will be larger. All this adds up to a cooler running machine that will last considerably longer than
an equivalent direct drive version. However, there is slightly more maintenance and considerably more dollars involved (10-30%
more). If you are using your pressure washer for industrial applications and expect to work with it almost every day, then this is
what you want. However, an equivalent direct drive machine will have the exact same performance for a lot less money.
The three most important factors in choosing a pump: QUALITY, QUALITY, QUALITY.
A lot of the low cost pressure washers with no-name pumps on them (or pumps on cheaper name brand machines) have very low
life expectancies (Some as low 60-100 hours). When buying a pressure washer, make sure you find out the life expectancy of the
pump. If the information is unavailable, stay clear because it is very likely that the manufacturer does not want you to know how
low it is. Another very important factor to consider is parts availability. KMS Tools tried being a warranty/service centre for some
low-end brands, however, parts availability and unreliability of these machines were so vast that we decided to no longer provide
this service. Before buying your machine, ask where you can get parts if you need them. After the sales person tells you, verify what
he is saying is accurate by actually contacting the business that was referred. KMS is often referred to by other retailers as a source
for parts and repairs for numerous brands that we do not service or repair.
If you are buying a new machine for $200 or less, expect it to be a disposable machine that might last you one season.
To prep your pump for winter flush it with clean water and prime it with anti-freeze. On gas models pull the rope slowly a few times
so that the pistons move around to make sure the anti-freeze cycles through the pump.
Engine
The engine is the part that powers the pump. The more powerful the engine (rated in HP), the greater the PSI and GPM that can be
produced. Engines are either gas or electric power and will typically have a life hour rating on them.
Electric Motors
These motors are very low maintenance and fairly quiet. There is also no exhaust so they can be used indoors or poorly ventilated
areas. Your typical electric pressure washer that is 110v and 15a will be fairly light duty because the engine is not strong enough to
generate much PSI or GPM.
Gas Engines
Generate much more power and are a lot more mobile because they do not need to plug into an electric power source. Since gas
engines are more powerful the pump can generate considerably more PSI and GPM so that they can clean faster and deeper than
any 110V electric pressure washer could. However, they do take a little more maintenance and cost more to operate. They must be
used in well ventilated areas because of carbon-monoxide fumes. All 4-cycle engines operate on regular unleaded gasoline. It is
strongly recommended to use fuel stabilizer if you do not use your machine often (or are winterizing it). Gasoline begins to break
down in a month and can start clogging up carburetors and fuel lines. Avoid this with some fuel stabilizer in the tank and in the jerry
can you store your fuel in.
When it comes right down to it, the two most important things to ask about the engine is how much horsepower it has and how
many hours it is rated for. The better quality the engine, the longer it will last. However, quality does not necessarily translate into
more power. You can have some excellent quality engines that can last you a very long time, but they were built to generate fairly
low power.
Accessories
Without these, your pressure washer is fairly useless. It would be like having a drill without any drill bits.
Pressure Washer Hose: Everything starts with the pressure washer hose. You will usually want 50 foot lengths as most people
tend to find 25 foot to be a too short for a lot of applications. Make sure you get a quality hose with the proper PSI rating to match
your machine. A poor quality hose will breakdown faster, is more susceptible to leaks and kinks and will usually be less flexible and
harder to work with.
The Wand: is the most common accessory and every pressure washer should come with one. You can change the spray pattern
with the different tips at the end depending on the application. From very narrow spray to generate higher pressure at the tip for
deeper cleaning to a wider spray that has less pressure but covers more area. Almost all pressure washers include a hose and wand.
Some very useful attachments include.
Dirt Blaster: This is a nozzle that goes on to the end of your wand. It has a very narrow spray that spins in a circular motion very
rapidly. This attachment is great because it can quickly clean hard surfaces very well and when used properly avoid the ‘tiger
stripping’ effect on your driveway that happens with conventional spray tips. I would avoid using this on soft materiel like wood
because it will damage it fairly quickly.
Extension/Telescoping wands: A wand that's adjustable up up to 18' or 24' in some cases for cleaning out of reach areas. This is
a great benefit if you need to reach up high so that you can avoid trying to pressure wash while standing on a ladder.
Gutter cleaners: This is a simple hooked piece that goes on the end of your wand. It lets you get into your gutters to clean them
out. Be careful though with high pressure machines, if you jamb them into your gutters carelessly the pressure can strip out the
caulking in your gutter joints (especially in the corners). If this happens your gutters will leak and will be an unpleasant repair
experience.
Whirl-a-Ways: These are a great addition also. They are a surface cleaning attachment with two rotating nozzles inside. The range
is in diameter from 12” to over 36”. These greatly speed up cleaning of any large flat area.
Ball Valve: This is one of my personal favorite items. It is a shut off lever that you put at the end of your hose. So if you want to
switch attachments you can turn off the water pressure/supply without having to walk back to your compressor and turning it off.
Hot Water Pressure Washers.
Hot Water Pressure washers are commercial machines with a built in water heaters. The cleaning power of the machines is
considerably more than a non-heated machine with comparable PSI and GPM because hot water simply cleans more effectively than
cold water. It breaks down and removes dirt and grime faster than a normal pressure washer can, reducing the amount of time you
need to spend cleaning. These also clean heavier stains (like grease) than non-heated pressure washers.
Do not feed hot water into a normal pressure water pump that was not designed for it. The heat will damage seals and O-rings.
Detergents
Detergents can greatly increase the speed of cleaning and help remove tough stains. Most pressure washers come equipped with a
venturi tube that will draw in the detergent from a bottle or pale and add it to the water stream. The detergent should be first
applied with a low pressure spray, given some time to do its work to break down the dirt then rinsed off with a normal high pressure
spray.
It is strongly recommended to use only pressure washer specific detergents. Using wrong detergents can clog your system and
potentially damage your pressure washer. Also be aware of the chemicals you are spraying to make sure they are environmentally
safe. Special permits may be needed for certain heavy duty industrial chemicals.
Final Words
When it comes right down to it, you need to buy a pressure washer that fits your application. There are many different types of
pressure washers from very low end electric machines to extremely powerful industrial machines. Before you buy a machine you
need to sit down and determine what you plan to use it for. One of the most important questions like ‘How much will I be using a
pressure washer?’ If you are a homeowner you will probably use it two or three days per year putting 20 hours' work on your
machine per year. In this case getting a machine rated for 500 hours will last you (if properly maintained) 25 years. However, if you
are working with it a part of your business you will want something rated for 2000 hours or more.
Also, you need to determine what applications you will be expecting the pressure washer to perform. If you are looking at doing
light occasional chores, such as cleaning smaller areas, cars, lawn equipment, dirt, algae then you would want around 4500 CPU. If
you are expecting to do more frequent work and bigger jobs such house siding, large areas of concrete, farm equipment then you
would want a machine than can produce 12,000 - 16,000 CPU. Commercial and contractors will want something rated around
25,000 CPU to do the extremely demanding jobs and heavy duty jobs and to speed up the cleaning process with the extra power.
Finally, plan in advance what attachments you will want in the future and make sure that the pressure washer you buy has enough
power to support them.