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

[Some Guy]

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).

[tnom]

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.

[cjt]

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.

[Jim Elbrecht]

-snip-

In other words. . . . "It depends on what you want to wash".

Jim

[ransley]

What are you washing

[Some Guy]

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?".

[George]

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.

[Some Guy]

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.

[sligoNoSPAMjoe]

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.

[KC]

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

[Jon Danniken]

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

[ransley]

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

[George]

but that is dependent on the supply.

[Pete C.]

They are independent.

PSI = Cleaning power as it dictates the water velocity and thus cleaning force.

GPM = Cleaning efficiency as it dictates the volume of high pressure water and therefore the area that the cleaning force can be applied to. The smaller the area, the longer it will take to clean a given surface area, just like a 22" lawn mower vs. a 60".

[dpb]

Well, that ain't exactly the whole story either...

The nozzle tip geometry has a great deal to do w/ the actual application of the water to the surface and the effect thereon for whatever the actual PSI/GPM ratings are...

--

[Ed Pawlowski]

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.

[Some Guy]

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.

[Pete C.]

Yes, but most any given pressure washer can accept different nozzles, the max PSI and GPM available to drive the nozzle don't change.

[Pete C.]

Pressure is in the hoses and lines up to the nozzle, there is no pressure after the nozzle, only velocity.

[ransley]

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.