We’ve heard people find some unexpected uses around the home for pressure cleaners - if you have one, how do you normally use yours?
My expectation is that the combination of pressure of water and volume of water should be a good predictor of cleaning efficiency, that is time to clean a given patch of concrete according to the How do we test spiel. I am ignoring ease of use here just trying to predict cleaning score with claimed pressure and volume.
According to my sums pressure and volume each predict cleaning marginally, when taken together almost not at all.
Does anybody have any idea why this is so? Is it because the claimed (not measured) figures for pressure and volume are fanciful or are there other factors at play that determine cleaning efficiency that we know nothing about?
Nozzle sizing. Pressure cleaners work by water velocity, which is also a function of the nozzle aperture.
Great to see the reviews and test results. Our pressure washer has a fault, which may or may not be repairable. I’ve considered the option of a replacement. I’ll be focussed on the lance design and performance. The pressure unit itself needs to be reliable and have a continuous duty rating, (Not listed in the specifications). As a rough guide I’ll also be comparing the pressure hose internal diameter and reach of the existing hose which is adequate around the home. Any that are shorter or less in diameter are possibly less capable than our current unit.
I’ve found that the adjustable lance on our Karcher which is 15+ years old the most useful. It can be adjusted progressively from a broad softer spray to a more concentrated spot spray. For each task there is a different optimal adjustment that works best. It has been used to clean paving, concrete and exposed aggregate drives.
The most recent task has been cleaning reclaimed hardwood decking boards following a scrub with a diluted cleaning agent. Being able to adjust the spray pattern and reduce the effective pressure on the boards has been useful. Also useful for the occasional clean of the Ute on the wider spray pattern, it seems to use less tank water than using a hose. Makes up for the low pressure from the house pump.
It’s possible performance factors include the design of the lance nozzles and preferences/choice of adjustable spray pattern.
The Choice operational performance test appears to be a combination of factors. The pressure pump output, the design of the lance/attachments and operator influence in choosing the optimal spray adjustment. The Choice testing team might like to clarify how they account for the last of these. @BrendanMays
That may be a factor but I don’t see how that explains it all.
If you make the nozzle smaller the velocity goes up but then friction and turbulence take hold. The result is that the amount of water that gets through will reduce so that the stream becomes less effective.
It becomes progressively ineffective because there is less mass and as the nozzle gets smaller the stream fragments into droplets, you have in effect a spray instead.
Small droplets have a large surface area and so they entrain more air as they move and so their velocity reduces very quickly due to air friction once they leave the nozzle.
Less mass and less velocity reaching the work material means less kinetic energy applied to shift dirt.
It looks to me that for any given pump their is an optimum nozzle size that is the most effective. Which leads to the question why would makers not make that simple optimisation?
This topic is very difficult as fluid dynamics is involved which is not well understood and involves higher maths to get even an approximate understanding.
Do we have any hydraulic engineers hereabouts?
I bought a Michelin MPX130BC (Sydney Tools exclusive) as recommended from a prior review. I suspect no Michelin was tested this time because of small market share resulting from the exclusive sourcing. It is one fine domestic pressure washer I would recommend to anyone near a Sydney Tools shop or game to order in.
Is good performance from a lower cost pressure washer more a good guess (or copy of one well proven design)?
The size of the aperture is only one aperture factor. There is also shape, roughness and edge characteristics which all affect the function of the nozzle at a particular pressure.
These factors can affect water velocities and also ability of a high pressure pump to maintain the specified pressure at the nozzle. Using only pressure and waterflow to determine performance will most likely give misleading performance, if functions of the nozzle aperture isn’t also considered.
It would be easier if the same nozzle was used on each pressure cleaner, as it would standardise the test and allow direct pressure cleaner performance. Unfortunately, while interesting, it would not be possible for (or relevant to) the average consumer to swap/exchange nozzles to replicate the test result to one bought for the home.
Having done fluid dynamics in some engineering subjects, it needs to also be considered. There are research papers which explain how these affect flow performance, but they are not overly relevant unless one knows the characteristics of the nozzles in question on a high pressure cleaner.
It’s similar in specification to our much older Kartcher V330 M. On the basic comparison of motor power and operating pressure the Michelin has a higher working pressure, slightly more powerful motor and weighs a few kgs heavier.
The current Kartcher models reviewed offer a 5+2 warranty, vs 3+2 for the Michelin store brand if that matters. Need to read the reviews of the current (members only). Not sure we can access the previous.
For consumers times have changed. The V330 M came with a basic 12 month warranty for private household use only.
I’ll not buy into the nozzle discussion. It’s a black art sprinkled with fairy dust.
For stubborn stains use Oxalic acid if you don’t use it already. It will bleach the wood but a sand of the wood will restore the colour back. As I have previously posted it will also clean most stains out of concrete particularly those annoying “rust” ones.
Here’s a list of items that you can clean with your pressure washer. Feel free to continue adding to the list
One thing we clean is walnuts. When walnuts fall off a tree, often the shells are covered with residues of the encasing fruit (which discolours and turns black). An easy way to remove most of these residues is place the walnuts into a plastic storage container with holes drilled in the bottom, and get the high pressure cleaner onto them. It makes a bit of a racket, but the nuts come out cleaner, ready for drying/maturing.
Edit: this is a video like the one we got the idea from…
It sure beats scrubbing them by hand.
Nice! I probably wouldn’t have thought about it, but since you mention there’s probably a few applications in the home garden for a pressure cleaner