Power/pressure washers: GPM & PSI - are they accurate, what is more important

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I'm looking at a few gasoline-powered pressure washers.
Naturally, the typical specs are:
a) the hp rating of the engine b) the gpm c) the psi
So my main question is - are these numbers fudged, or have a wide accuracy range?
What is the minumum rating (in terms of gpm and /or psi) that make it worth while to actually buy one of these things?
The range I see are from 2 to 4 GPM, and roughly 2000 to 4000 psi. Engine HP from 6 to 13.
Your answer should not include "it depends on what you want to wash".
I want to know if a washer that does 2 gpm @ 2000 psi has only half the "cleaning power" as one that can do 4 gpm at 4000 psi (ie does the cleaning power scale linearly with these numbers, or geometrically or exponentially).
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The second is 4 times better. Anything can give you pressure. Even your grease gun can give you 10,000psi. The GPM rating far outweighs the pressure rating.
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snipped-for-privacy@mucks.net wrote:

but that is dependent on the supply.
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Some Guy wrote:

IMHO -
If you focus the stream, the pressure indicates how intense that stream will be. The GPM indicates how large an area you can clean per swath at a particular pressure. So if your concern is cutting through tough dirt in small areas, the pressure might be more interesting. If your concern is covering large areas in a reasonable time, the GPM might be what you want to look at.
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-snip-
In other words. . . . "It depends on what you want to wash".<g>
Jim
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What are you washing
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ransley wrote:

I think that is the more relavent question here.

Today it might be one thing.
Tommorrow it might be something else. Next year something completely different.
Now do you see why asking "what do you want to wash" is irrelavent?
If I wanted to buy a set of wrenches, or a drill, would you be asking "what want to assemble / disassemble?" or "what do you want to drill?".
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Some Guy wrote:

If it was irrelevant why would you even need to ask?

In the case of a drill are you hanging curtains or using it in your steel erection business? Maybe a crappy harbor freight $9 drill will be OK for the curtains.
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George wrote:

Still not willing to answer that question eh?

Ask what?
I'm not the one asking "what do you want to wash?". I'm the one saying "don't ask me that question".
How about this. I want to use it to wash my windows one day and carve granite statuary another day. Does that help?
I'm asking if the GPM and PSI numbers (and engine HP numbers) can be trusted from one make/model to the next.
I'm asking what are the minimum GPM, PSI and engine HP numbers that make it worth while to buy and use these things.

Don't you think that if I had a "steel erection business" that I'd probably have periodic contact with sales consultants for products that you will never see in a Lowes or Home Depot and I would probably already have several industrial-grade drills for us in my business?
Do you have to resort to that level of hyperbole to make an inconsequential point?
If you have no actual experience owning / using a pressure washer, then don't waste my time.
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Some Guy wrote:

You don't use a pressure washer to wash windows. You use a brush on a stick and a hose or a bucket and a rag.
You might even consider a sponge and a squeegee.
I will leave the topic of window cleaning solutions for another discussion.
Jon
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...

    I hope you are not planning to use the same tools for both.

    Not very. They both likely will have inflated their numbers. This kind of misrepresentation is most common on consumer grade tools than professional or industrial.

    It depends on what you want to use it on. I would go a little further and suggest that not only what you want to use it on but also what make and model tool, not just the GPM and PSI.
    Sort of like asking what the Towing capacity and the fuel tank capacity is needed for for a car and not telling us what you want to do with that car. We might guess you want to tow a boat, but that could be a 40 foot power boat or a 10 foot row boat.
    Would you tell you doctor you have a pain, and you want to know what to do about it and refuse to tell him where the pain is, or when you feel it?

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snipped-for-privacy@hotmail.com wrote:

Can you cite any authoritative source that has done any sort of analysis of several models of home, farm or light-commercial grade power washers and has come to that conclusion or made that observation?
It's highly likely that what you say is true - just like the HP numbers quoted for small gasoline engines have been in recent years. But I would like to see something in print stating their observations or measurements of these power washers.
Do you own or use any power washers?

Would you buy a washer rated at 500 psi and 1 gpm? If not, why not?

Even if I were to tell you, do you have the personal experience to know how many GPM/PSI is needed to do task 1, task 2, task 3 and task 4? Are you asking because if I tell you what task 1 is, you can tell me authoritatively, specifically, how many gpm and PSI I need?

Are you the doctor in this situation?
If I describe exactly what I want to clean, can YOU tell me the minimum PSI and GPM I need?
Or do you just like answering a question with another question?
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    I have seen some test results, but nothing conclusive. I would expect that the numbers are real and under the specific text conditions, they are valid. The problem is each manufacturer, or even different models may be measured using different methods.

Yes
    No. I would need to have more detailed information about the equipment on the market, which I have never seen, and there would be the difference in what I would consider minimum and what you would consider minimum.
If time is no issue, then why use a power washer at all. a standard hose will do the job. It may take weeks, but that 30 psi will do it in time.

    I love answering questions with a question when the initial question needs clarification.
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I just aquired a 1800psi 2 gpm with a B&S 4.5HP. It will peal paint. I was using a 1300 PSI electric that I thought was pretty good. For the typical non-professional consumer (like me), the 1800/2GPM will do most of what you want to do. If it is too powerful, hold the tip farther fromt he surface to be cleaned. Also, there are an array of tips that can be bought that will fit most jobs. Or, get an adjustable one.
Hank <~~~keeping it simple
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You dont get it, its all about what you wash, if its a 10ft side walk, or a lawnmower its one need, if its a mud caked dump truck or a 500ft building its another. Ive used the best units and the least powerfull, sizing a tool is whats important like I dont use my 1/2 " hammer drill to drill a 1/16" hole, but maybe you do. On that note id rather have more gpm than pressure for my minimal needs
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ransley wrote:

I can understand that if I'm washing something tough/nasty all day long because it's my job, that I don't necessarily want the smallest nozzle and spend a lot of time cleaning one spot because it's all my machine is capable of.
There must be some minimum amount of PSI/GPM rating to make these things worth buying for home or light commercial use.
And nobody has yet to comment on the power rating of the engine.
Since the engine is the real power behind these washers, how can it be explained that there is such a wide range of power (from 5 hp to 15 hp) yet the PSI and GPM numbers don't change very much, and sometimes two different washers with identical GPM/PSI rating will have vastly different engine HP rating.
I'm also looking at a sand pickup attachment (for wet sandblasting) that claims to have a minimum requirement of 3 gpm @ 1500 psi.
http://www.princessauto.com/vmchk/shop-garage/pressure-washer-accessories/washer-accessories/8067399-wet-sandblast-kit
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For light use my electric karcher is fine, its maybe 2 gpm at 1300 psi, a 13hp commercial unit may accept 6 gpm or more so it has the extra power but my supplys are under 5gpm, sometimes 3gpm. Measure your faucet gpm because buying more is a waste of money. For ocasional use a 15 or 30a electric might be smarter, there are electrics that use 3-5 gpm. Doing windows and carving granite are not what you get a power washer for. So the questions of its use, are what determine what is best, ive used the bigest Honda, I dont want one, it would be overkill for me.
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    Yes, expect a lot of fudging.

    It depends greatly on the type of work and the quantity of it.

    Sorry but what you want to wash is a critical part of the choice. A large sledge hammer is good for splitting logs, but it is not very good at cutting diamonds.

    Depends. Some things clean up best with more volume and less pressure and others with more pressure and less volume. In both cases it generally is faster - better with more volume and pressure.
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From a homeowners useage point of view you will 'never' need more than 2500psi, however you will often wish you had more than 2 GPM. With 2500psi you can easily carve your initials in your wooden deck, remove paint from your car, and blow window panes out of their mountings.
KC
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The numbers are real, but they are also somewhat meaningless other than rough comparison. While you don't want to hear "it depends", in actual use, it does. The rating figure is for the water coming out of the tip at close range. In actual use, the 2000 psi unit held at a food or two is giving the same pressure at the 4000 psi unit held a longer distance, and the object of being cleaned in receiving far less than the rated numbers.
My experience is limited to a 2500 psi model and I've never wanted more, either at home or at the shop. OTOH, if I wad dong heavy cleaning of power plants every day, I'd go with bigger.
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